readme: add a few links

.clang-format

@@ -0,0 +1,9 @@
+---
+Language:        Cpp
+BasedOnStyle:  LLVM
+ConstructorInitializerIndentWidth: 8
+ContinuationIndentWidth: 8
+IndentWidth:     4
+InsertNewlineAtEOF: true
+PointerAlignment: Left
+SpacesBeforeTrailingComments: 2

.gitignore

@@ -1,3 +1,5 @@
 *.bin
+*.o
+*.elf
+*.com
 polos.img
-polmon.com

Dockerfile

@@ -17,7 +17,7 @@ FROM deps AS build
 
 ARG TARGET
 
-ADD . /workspace
+ADD ./src /workspace
 WORKDIR /workspace
 RUN make ${TARGET}
 

Makefile

@@ -1,86 +1,25 @@
 dev-image = 5150-dev
 
-%.bin: %.asm
-	nasm $? -o $@
-
-crc16.s: crc16.c
-	ia16-elf-gcc -S -Os -o crc16.s crc16.c
-
-crc16.bin: crc16.s crt0.c
-	ia16-elf-gcc -o crc16.bin -Os -nostdlib crc16.s crt0.c
-
-CC = ia16-elf-gcc
-CXX = ia16-elf-gcc
-LD = ia16-elf-gcc
-CXXFLAGS = -mregparmcall -ffunction-sections -Os -flto
-CFLAGS = -mregparmcall -ffunction-sections -Os -flto
-LDFLAGS = -mregparmcall -Wl,--gc-sections -Os -nostdlib -flto
-
-%.elf:
-	$(LD) $(LDFLAGS) $(CPPFLAGS) -o $@ $^
-
-bootsectors = fat12boot.bin wozmon.bin
-
-$(bootsectors):
-	ia16-elf-objcopy -O binary $? $@
-	truncate -s 510 $@
-	printf "\125\252" >> $@
-
-fat12boot.elf: fat12boot.o fat12.o bootsect.S
-fat12boot.elf: LDFLAGS += -T bootsect.ld
-
-fat12boot.bin: fat12boot.elf
-
-polmon.elf: LDFLAGS += -T flat0600.ld
-polmon.elf: polmon.o
-
-polmon.com: polmon.elf
-	ia16-elf-objcopy -O binary $? $@
-
-wozmon.o: polmon.cc
-wozmon.o: CPPFLAGS = -DWOZMON=1
-wozmon.o:
-	$(CXX) $(CXXFLAGS) $(CPPFLAGS) -c -o $@ $<
-
-wozmon.elf: wozmon.o bootsect.S
-wozmon.elf: LDFLAGS += -T bootsect.ld
-wozmon.elf: CPPFLAGS += -DNOBPB
-
-wozmon.bin: wozmon.elf
-
-polos.img: fat12boot.bin polmon.com
-	dd if=/dev/zero of=$@ bs=512 count=720
-	mformat -i $@ -t 40 -h 2 -s 9
-	mcopy -i $@ polmon.com ::/polmon.com
-	dd if=fat12boot.bin of=$@ conv=notrunc
-
-.PHONY: clean
-clean:			## Remove generated files
-	rm -rf *.bin polmon.com polos.img
-
 .PHONY: dev-image
 dev-image:
 	docker build -t $(dev-image) --target dev .
 
 .PHONY: dev
 dev: dev-image	## Launch a dev container
-	docker run -it --rm -v $(CURDIR):/workspace $(dev-image)
+	docker run -it --rm -v $(CURDIR)/src:/workspace $(dev-image)
 
 
 .PHONY: binaries
-binaries:		## Build all binaries
+binaries:		## Build all small binaries
+	docker build --build-arg TARGET=call.bin -o . --target=export .
 	docker build --build-arg TARGET=readfloppy.bin -o . --target=export .
 	docker build --build-arg TARGET=writefloppy.bin -o . --target=export .
-	docker build --build-arg TARGET=crc16.bin -o . --target=export .
-	docker build --build-arg TARGET=wozmon.bin -o . --target=export .
-	docker build --build-arg TARGET=hello.bin -o . --target=export .
 	docker build --build-arg TARGET=copy.bin -o . --target=export .
-	docker build --build-arg TARGET=call.bin -o . --target=export .
-	docker build --build-arg TARGET=debug.bin -o . --target=export .
-	docker build --build-arg TARGET=dosdbt.bin -o . --target=export .
 	docker build --build-arg TARGET=format.bin -o . --target=export .
-	docker build --build-arg TARGET=polmon.com -o . --target=export .
-	docker build --build-arg TARGET=fat12boot.bin -o . --target=export .
+	docker build --build-arg TARGET=crc16.bin -o . --target=export .
+	docker build --build-arg TARGET=hello.bin -o . --target=export .
+	docker build --build-arg TARGET=readio.bin -o . --target=export .
+	docker build --build-arg TARGET=writeio.bin -o . --target=export .
 
 .PHONY: floppy
 floppy:			## Make a bootable floppy image

README.md

@@ -1,26 +1,123 @@
 5150 stuff
 ==========
 
-The binary programs here use multiple conventions (more Fun!):
-- .asm files use NASM syntax and are built with `nasm xx.asm`
-- .s files use GAS syntax, they are built with `ia16-elf-gcc`
+## Layout of a bootable polOS floppy disk
 
-The reason is uh, because you see, I did things.
+The floppy disk is FAT12 formatted. It must contain at least the following items:
 
-The .asm came first and was copy pasta from the internet.
-The .s files came from the output of `ia16-elf-gcc -S` when I couldn't be bothered to write programs in assembly but still needed to make them compatible with BASIC's *CALL* instruction.
+* _fat12boot.bin_: the boot sector. It loads _polio.com_ from a FAT12-formatted
+    drive 0 to address _0x0600_ and jumps to it.
+* _polio.com_: the basic OS functions. It serves all interrupt 0x80 functions
+    (see below) and loads _polmon.com_ to address _0x1200_, then jumps to it.
+* _polmon.com_: a barebones memory utility. See below for all it can do.
 
-Also the wozmon binary contains special care to make it into a boot sector (0xaa55 magic).
+## polOS int 0x80
+
+* function in AH
+* optional argument in AL
+* other arguments on the stack
+* return value in AX
+
+| AH | AL | stack arguments | return | description |
+| --- | --- | --- | --- | --- |
+| _0x01_ | | _addr_, _c_, _h_, _s_ | error code in AH | __readsector__: reads 1 floppy sector at _c/h/s_ into _0000:addr_ |
+| _0x02_ | | _addr_, _c_, _h_, _s_ | error code in AH | __writesector__: writes 1 floppy sector at _c/h/s_ from _0000:addr_ |
+| 0x03 | | _c_, _h_ | error code in AH | __formattrack__: formats 1 track at c/h |
+| 0x04 | | _fname_, _addr_ | non-zero if error | __readfile__: reads file with name at _ds:fname_ into _ds:addr_ |
+| 0x05 | | _addr_, _size_ | bytes received, < 0 if error | __recvpara__: receive at most _size_ bytes  from parallel port into _ds:addr_ |
+| 0x06 | | _addr_, _size_ | bytes sent, < 0 if error | __sendpara__: send at most _size_ bytes to parallel port from _ds:addr_ |
+| 0x07 | _until-idle_ | | 0 if idle | __runpara__: run a round of parallel comms if _AL=0_, keep going until idle if _AL!=0_ |
+| 0x08 | | _fname_, _addr_, _size_ | error code in AH | __writefile__: writes _size_ bytes from _ds:addr_ into file with name at _ds:fname_ |
+
+
+## polmon commands
+
+Commands are a single letter followed by an optional space and arguments, with optional spaces between them.
+A command can be prefixed with up to 4 hex digits, which will then change the current address.
+
+* (no command): dumps 16 bytes at the current address. If no address is given, also increments the current address by 16.
+* `w bytes:[u8]*`: writes bytes in hex to the current address.
+* `k src:u16 size:u16`: copy _size_ bytes of memory from _cur-seg_:_src_ to _cur-seg:cur-addr_
+* `s seg:u16`: changes the current segment
+* `j`: calls a function at the current address. ABI calling conventions below.
+* `l file:str`: loads a program with given name into the current segment, address _0x0100_.
+* `r args:[u16]*`: runs the program in the current segment with arguments.
+* `i ax:u16 args:[u16]*`: call an int 0x80 function with given AX and stack args. See section above.
+
+The _r_, _j_ and _i_ commands display the value of the AX register after returning to polmon.
+
+### ABI convention for (j)umping to functions
+
+* AX, BX, CX, DX are caller-saved, all others are callee-saved
+* first 3 arguments passed in AX, DX and CX, others are pushed in reverse order (former argument in lower memory)
+* return value in AX
+
+
+### ABI for programs
+
+See example in _hello.com_
+
+
+## Examples
+
+### Launching mushroom client
 
-Anyway, just type
 ```
-make binaries
+s 200
+l mushroom.com
+r
 ```
 
-and stop whining.
+### FTP a file and store it to the floppy disk
 
+```
+s 200
+l ftpget.com
+```
+
+* switch to segment _0x200_
+* load file _ftpget.com_ to _cur-seg:0100_
+
+Here you need to run this on the host:
+```
+python ftpserve.py src/hello.com
+```
+
+Then on polOS:
+```
+r f000 200
+s 0
+6000
+w 48454c4c4f202020434f4d
+i 0800 6000 f000 200
+```
+
+* run previously loaded `ftpget.com`: store up to _0x200_ (512) bytes to address _0000:f000_
+* set _cur-seg_ to _0x0000_
+* set _cur-add_ to _0x6000_
+* write file name in ascii: `HELLO   COM` to _0000:6000_
+* call int 0x80 0x08 (writefile) with args: _fname_, _addr_, _size_
+
+
+We can now test that the program got transferred correctly:
+```
+s 300
+l hello.com
+r
+```
+
+### But where is my `ls` command?
+
+You can just inspect memory at _0000:1c00_, that's the root directory. Each entry is _0x20_ (32) bytes long and starts with 11 characters that constitute the file name.
 
 ## Useful stuff
 
 * [Colab](https://colab.research.google.com/drive/1xGKYQJLKyabcSNYOiPumf9_-bbCbXke1?usp=sharing)
 * [Arduino pinout](https://docs.google.com/spreadsheets/d/1jgKhr-0MFtY_bFZL9xYwVsxFPt4u_5ItV8Rj7FQ7Kj4/edit)
+* [DOS 3.1 disk images](https://dl.winworldpc.com/Abandonware%20Operating%20Systems/PC/DOS/IBM/IBM%20PC-DOS%203.1%20%285.25%29.7z)
+* [DOS 3.1 manual](https://dl.winworldpc.com/IBM%20PC-DOS%203.10%20Manuals%20Feb85.7z)
+* [IBM 5150 BIOS ROM](https://www.minuszerodegrees.net/bios/BIOS_IBM5150_19OCT81_5700671_U33.BIN)
+* [IBM Cassette BASIC C1.00](https://www.minuszerodegrees.net/rom/bin/IBM/IBM%205150%20-%20Cassette%20BASIC%20version%20C1.00.zip)
+* [IBM 5150 technical ref](https://www.minuszerodegrees.net/manuals/IBM/IBM_5150_Technical_Reference_6025005_AUG81.pdf)
+* [Ruud's diagnostic ROM](https://minuszerodegrees.net/ruuds_diagnostic_rom/bin/ruuds_diagnostic_rom_v5.4_8kb.zip)
+* [Supersoft diagnostic ROM](https://www.minuszerodegrees.net/supersoft_landmark/Supersoft_PCXT_8KB.bin)

arduino/kbd/kbd.cc

@@ -0,0 +1,193 @@
+// keyboard wiring diagram:
+// https://www.minuszerodegrees.net/5150/misc/5150_keyboard_reset.jpg
+
+#include "Arduino.h"
+
+constexpr int kClockPin = PC6;
+constexpr int kDataPin = PC4;
+
+constexpr int kBitDelayMicros = 100;
+constexpr int kCodeDelayMicros = 200;
+constexpr int kKeyDelayMicros = 100;
+
+namespace {
+
+void sendCode(int code) {
+    // preconditions: clock and data pins are INPUT
+
+    while (digitalRead(kDataPin) == LOW || digitalRead(kClockPin) == LOW) {
+        // wait. we're not allowed to send
+    }
+
+    digitalWrite(kDataPin, LOW);
+    digitalWrite(kClockPin, LOW);
+
+    pinMode(kClockPin, OUTPUT);
+    delayMicroseconds(kBitDelayMicros);
+    pinMode(kClockPin, INPUT);
+    // delayMicroseconds(kDelayMicros);
+
+    for (int i = 0; i < 8; i++) {
+        if ((code & (1 << i)) == 0) {
+            // send a 0
+            pinMode(kDataPin, OUTPUT);
+        } // else do nothing, it's already a 1
+        delayMicroseconds(kBitDelayMicros);
+
+        pinMode(kClockPin, OUTPUT);
+        delayMicroseconds(kBitDelayMicros);
+        pinMode(kDataPin, INPUT);
+        pinMode(kClockPin, INPUT);
+    }
+    delayMicroseconds(kCodeDelayMicros);
+}
+
+enum State {
+    kReady,
+    kMaybeReset,
+};
+
+constexpr int kResetDelay = 19;
+
+constexpr int kLetterCodes[] = {
+        0x1E, // 'a'
+        0x30, 0x2E, 0x20, 0x12, 0x21, 0x22, 0x23, 0x17, 0x24,
+        0x25, 0x26, 0x32, 0x31, 0x18, 0x19, 0x10, 0x13, 0x1F,
+        0x14, 0x16, 0x2F, 0x11, 0x2D, 0x15, 0x2c,
+};
+
+constexpr int kNumberCodes[] = {
+        0x0B, // '0'
+        0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A,
+};
+
+void sendNormalCode(int code) {
+    sendCode(code);
+    sendCode(code | 0x80);
+}
+
+void sendShiftCode(int code) {
+    sendCode(42); // left shift
+    sendNormalCode(code);
+    sendCode(42 | 0x80);
+}
+
+void sendCtrlAltDel() {
+    sendCode(0x1d); // ctrl
+    sendCode(0x38); // alt
+    sendCode(0x53); // del
+    sendCode(0x53 | 0x80);
+    sendCode(0x38 | 0x80);
+    sendCode(0x1d | 0x80);
+}
+
+void sendCtrlBreak() {
+    sendCode(0x1d); // ctrl
+    sendCode(0x46); // break
+    sendCode(0x46 | 0x80);
+    sendCode(0x1d | 0x80);
+}
+
+} // namespace
+
+void sendAsciiChar(int c) {
+    if (c >= 'a' && c <= 'z') {
+        return sendNormalCode(kLetterCodes[c - 'a']);
+    } else if (c >= '0' && c <= '9') {
+        return sendNormalCode(kNumberCodes[c - '0']);
+    } else if (c >= 'A' && c <= 'Z') {
+        return sendShiftCode(kLetterCodes[c - 'A']);
+    }
+    switch (c) {
+    case '-':
+        return sendNormalCode(12);
+    case '=':
+        return sendNormalCode(13);
+    case '[':
+        return sendNormalCode(26);
+    case ']':
+        return sendNormalCode(27);
+    case ';':
+        return sendNormalCode(39);
+    case '\'':
+        return sendNormalCode(40);
+    case ',':
+        return sendNormalCode(51);
+    case '.':
+        return sendNormalCode(52);
+    case '/':
+        return sendNormalCode(53);
+    case ' ':
+        return sendNormalCode(57);
+    case '\n':
+        return sendNormalCode(28);
+
+    case '!':
+        return sendShiftCode(2);
+    case '@':
+        return sendShiftCode(3);
+    case '#':
+        return sendShiftCode(4);
+    case '$':
+        return sendShiftCode(5);
+    case '%':
+        return sendShiftCode(6);
+    case '^':
+        return sendShiftCode(7);
+    case '&':
+        return sendShiftCode(8);
+    case '*':
+        return sendShiftCode(9);
+    case '(':
+        return sendShiftCode(10);
+    case ')':
+        return sendShiftCode(11);
+    case '_':
+        return sendShiftCode(12);
+    case '+':
+        return sendShiftCode(13);
+
+    case '{':
+        return sendShiftCode(26);
+    case '}':
+        return sendShiftCode(27);
+    case ':':
+        return sendShiftCode(39);
+    case '"':
+        return sendShiftCode(40);
+    case '<':
+        return sendShiftCode(51);
+    case '>':
+        return sendShiftCode(52);
+    case '?':
+        return sendShiftCode(53);
+
+    case 0:
+        return sendCtrlAltDel();
+    case 27:
+        return sendCtrlBreak(); // escape
+    }
+}
+
+void setupKbd() {
+    pinMode(kClockPin, INPUT);
+    pinMode(kDataPin, INPUT);
+}
+
+void checkKbdReset() {
+    static State state = kReady;
+    static int lastclocklow = 0;
+
+    int clockp = digitalRead(kClockPin);
+    if (state == State::kReady && clockp == LOW) {
+        state = State::kMaybeReset;
+        lastclocklow = millis();
+    } else if (state == State::kMaybeReset) {
+        if (clockp == HIGH && millis() - lastclocklow > kResetDelay) {
+            delay(1);
+            state = State::kReady;
+            sendCode(0xaa);
+            Serial.println("Reset!");
+        }
+    }
+}

arduino/kbd/kbd.h

@@ -0,0 +1,5 @@
+#pragma once
+
+void sendAsciiChar(int c);
+void setupKbd();
+void checkKbdReset();

arduino/kbd/kbd.ino

@@ -1,213 +1,74 @@
-// keyboard wiring diagram: https://www.minuszerodegrees.net/5150/misc/5150_keyboard_reset.jpg
+#include "kbd.h"
+#include "paracomm.h"
+#include "parallel.h"
 
-constexpr int kClockPin = PC6;
-constexpr int kDataPin = PC4;
+#ifndef NOKBD
+#define NOKBD 1
+#endif  // NOKBD
 
-constexpr int kBitDelayMicros = 100;
-constexpr int kCodeDelayMicros = 200;
-constexpr int kKeyDelayMicros = 100;
+ParaComms pc;
 
 void setup() {
-  // put your setup code here, to run once:
-  Serial.begin(115200);
-  pinMode(LED_BUILTIN, OUTPUT);
+    // put your setup code here, to run once:
+    Serial.begin(115200);
+    pinMode(LED_BUILTIN, OUTPUT);
 
-  pinMode(kClockPin, INPUT);
-  pinMode(kDataPin, INPUT);
+    setupKbd();
+    setupParallel();
 
-  Serial.println("kbd 0.1");
-}
+    pc = ParaComms{
+            .mosi_cb =
+                    [](uint8_t* data, uint8_t len) {
+                        for (int i = 0; i < len; i++) {
+                            Serial.printf("%c", data[i]);
+                        }
+                    },
+    };
 
-// 0. reset
-// 0.0. clock line will be held low externally for 20 ms
-//      when back up, keyboard needs to clock 0xAA as a response
-//
-// 1. operation
-// 1.0. just directly clock out scan codes of pressed keys
-
-void sendCode(int code) {
-  Serial.printf("sending code 0x%02x\n", code);
-  // preconditions: clock and data pins are INPUT
-
-  while (digitalRead(kDataPin) == LOW || digitalRead(kClockPin) == LOW) {
-    // wait. we're not allowed to send
-  }
-
-  digitalWrite(kDataPin, LOW);
-  digitalWrite(kClockPin, LOW);
-
-  pinMode(kClockPin, OUTPUT);
-  delayMicroseconds(kBitDelayMicros);
-  pinMode(kClockPin, INPUT);
- // delayMicroseconds(kDelayMicros);
-
-  for (int i = 0; i < 8; i++) {
-    if ((code & (1 << i)) == 0) {
-      // send a 0
-      pinMode(kDataPin, OUTPUT);
-    }  // else do nothing, it's already a 1
-    delayMicroseconds(kBitDelayMicros);
-
-    pinMode(kClockPin, OUTPUT);
-    delayMicroseconds(kBitDelayMicros);
-    pinMode(kDataPin, INPUT);
-    pinMode(kClockPin, INPUT);
-  }
-  delayMicroseconds(kCodeDelayMicros);
-}
-
-enum State {
-  kReady,
-  kMaybeReset,
-};
-
-constexpr int kResetDelay = 19;
-
-State state = State::kReady;
-int lastclocklow = 0;
-
-constexpr int kLetterCodes[] = {
-  0x1E,  // 'a'
-  0x30,
-  0x2E,
-  0x20,
-  0x12,
-  0x21,
-  0x22,
-  0x23,
-  0x17,
-  0x24,
-  0x25,
-  0x26,
-  0x32,
-  0x31,
-  0x18,
-  0x19,
-  0x10,
-  0x13,
-  0x1F,
-  0x14,
-  0x16,
-  0x2F,
-  0x11,
-  0x2D,
-  0x15,
-  0x2c,
-};
-
-constexpr int kNumberCodes[] = {
-  0x0B,  // '0'
-  0x02,
-  0x03,
-  0x04,
-  0x05,
-  0x06,
-  0x07,
-  0x08,
-  0x09,
-  0x0A,
-};
-
-void sendNormalCode(int code) {
-  sendCode(code);
-  sendCode(code | 0x80);
-}
-
-void sendShiftCode(int code) {
-  sendCode(42); // left shift
-  sendNormalCode(code);
-  sendCode(42 | 0x80);
-}
-
-void sendCtrlAltDel() {
-  sendCode(0x1d);  // ctrl
-  sendCode(0x38);  // alt
-  sendCode(0x53);  // del
-  sendCode(0x53 | 0x80);
-  sendCode(0x38 | 0x80);
-  sendCode(0x1d | 0x80);
-}
-
-void sendCtrlBreak() {
-  sendCode(0x1d);  // ctrl
-  sendCode(0x46);  // break
-  sendCode(0x46 | 0x80);
-  sendCode(0x1d | 0x80);
-}
-
-void sendAsciiChar(int c) {
-  if (c >= 'a' && c <= 'z') {
-    return sendNormalCode(kLetterCodes[c - 'a']);
-  } else if (c >= '0' && c <= '9') {
-    return sendNormalCode(kNumberCodes[c - '0']);
-  } else if (c >= 'A' && c <= 'Z') {
-    return sendShiftCode(kLetterCodes[c - 'A']);
-  }
-  switch (c) {
-    case '-': return sendNormalCode(12);
-    case '=': return sendNormalCode(13);
-    case '[': return sendNormalCode(26);
-    case ']': return sendNormalCode(27);
-    case ';': return sendNormalCode(39);
-    case '\'': return sendNormalCode(40);
-    case ',': return sendNormalCode(51);
-    case '.': return sendNormalCode(52);
-    case '/': return sendNormalCode(53);
-    case ' ': return sendNormalCode(57);
-    case '\n': return sendNormalCode(28);
-
-    case '!': return sendShiftCode(2);
-    case '@': return sendShiftCode(3);
-    case '#': return sendShiftCode(4);
-    case '$': return sendShiftCode(5);
-    case '%': return sendShiftCode(6);
-    case '^': return sendShiftCode(7);
-    case '&': return sendShiftCode(8);
-    case '*': return sendShiftCode(9);
-    case '(': return sendShiftCode(10);
-    case ')': return sendShiftCode(11);
-    case '_': return sendShiftCode(12);
-    case '+': return sendShiftCode(13);
-
-    case '{': return sendShiftCode(26);
-    case '}': return sendShiftCode(27);
-    case ':': return sendShiftCode(39);
-    case '"': return sendShiftCode(40);
-    case '<': return sendShiftCode(51);
-    case '>': return sendShiftCode(52);
-    case '?': return sendShiftCode(53);
-
-    case 0: return sendCtrlAltDel();
-    case 27: return sendCtrlBreak();  // escape
-  }
+    Serial.println("kbd 0.1");
 }
 
 void loop() {
-  static int led_counter = 0;
-  static int led = HIGH;
-  if (led_counter > 400000) {
-    led_counter = 0;
-    led = (led == HIGH) ? LOW : HIGH;
-    digitalWrite(LED_BUILTIN, led);
-  }
-  led_counter += 1;
+    static int led_counter = 0;
+    static int led = HIGH;
 
-  int clockp = digitalRead(kClockPin);
-  if (state == State::kReady && clockp == LOW) {
-    state = State::kMaybeReset;
-    lastclocklow = millis();
-  } else if (state == State::kMaybeReset) {
-    if (clockp == HIGH && millis() - lastclocklow > kResetDelay) {
-      delay(1);
-      state = State::kReady;
-      sendCode(0xaa);
-      Serial.println("Reset!");
+    static int mode = 0;  // 0 = keyboard, 1 = parallel
+
+    if (led_counter > 400000) {
+        led_counter = 0;
+        led = (led == HIGH) ? LOW : HIGH;
+        digitalWrite(LED_BUILTIN, led);
     }
-  }
+    led_counter += 1;
 
-  if (Serial.available() > 0) {
-    int c = Serial.read();
-    sendAsciiChar(c);
-    //delayMicroseconds(kKeyDelayMicros);
-  }
+#if NOKBD
+#else  // NOKBD
+    checkKbdReset();
+#endif  // NOKBD
+
+    uint8_t mosib;
+    if (strobeOccurred(mosib)) {
+        pc.FeedMosiData(mosib);
+        uint8_t misob = pc.NextMisoNibble();
+        writeParallel(misob);
+    }
+
+    if (Serial.available() > 0) {
+        int c = Serial.read();
+#if NOKBD
+        pc.SendByte(c);
+#else  // NOKBD
+        if (c == 2) {
+            mode = 0;
+        } else if (c == 3) {
+            mode = 1;
+        } else {
+            if (mode == 0) {
+                sendAsciiChar(c);
+            } else {
+                pc.SendByte(c);
+            }
+        }
+#endif  // NOKBD
+    }
 }

arduino/kbd/paracomm.h

@@ -0,0 +1,124 @@
+#pragma once
+
+#include <stdint.h>
+
+struct ParaComms {
+    using MessageCallback = void (*)(uint8_t *, uint8_t);
+    enum State {
+        kIdle,
+        kLength,
+        kLength2, // for miso
+        kData,
+        // kCrc,  // ?
+    };
+    static constexpr uint8_t kMosiStartByte = 0x42;
+    static constexpr uint8_t kIdleByte = 0x00;
+    static constexpr uint8_t kMisoStartNibble = 0xa;
+    static constexpr uint8_t kMisoIdleNibble = 0x0;
+
+    MessageCallback mosi_cb = nullptr;
+    uint8_t *miso_buffer = nullptr;
+    uint8_t miso_size = 0;
+    uint8_t miso_nibbles_sent = 0;
+    State miso_state = kIdle;
+
+    // double work buffer. one being sent, one being written to
+    uint8_t miso_workbuf[2][256];
+    uint8_t miso_workbuf_idx = 0;
+    uint8_t miso_workbuf_size = 0;
+
+    uint8_t mosi_buffer[256];
+    uint8_t mosi_size = 0;
+    uint8_t mosi_received = 0;
+    State mosi_state = kIdle;
+
+    void SwapBuffers() {
+        miso_buffer = miso_workbuf[miso_workbuf_idx];
+        miso_size = miso_workbuf_size;
+
+        miso_workbuf_idx = (miso_workbuf_idx + 1) % 2;
+        miso_workbuf_size = 0;
+    }
+
+    int SendByte(uint8_t b) {
+        if (miso_workbuf_size == 256) {
+            return -1; // sorry we're full
+        }
+
+        uint8_t *buff = miso_workbuf[miso_workbuf_idx];
+        buff[miso_workbuf_size] = b;
+        miso_workbuf_size += 1;
+
+        return 0;
+    }
+
+    void FeedMosiData(uint8_t b) {
+        switch (mosi_state) {
+        case kIdle:
+            // check start byte
+            if (b == kMosiStartByte) {
+                mosi_state = kLength;
+            } else if (b == kIdleByte) {
+                // just twiddling our thumb drives
+            } else {
+                // Serial.printf("sp: %02x\n", b);
+            }
+            break;
+        case kLength:
+            // assert(b > 0)
+            mosi_size = b;
+            mosi_received = 0;
+            mosi_state = kData;
+            break;
+        case kData:
+            mosi_buffer[mosi_received] = b;
+            mosi_received += 1;
+
+            if (mosi_received == mosi_size) {
+                if (mosi_cb != nullptr) {
+                    mosi_cb(mosi_buffer, mosi_received);
+                }
+                mosi_state = kIdle;
+            }
+        case kLength2: // error
+            return;
+        }
+    }
+
+    uint8_t NextMisoNibble() {
+        switch (miso_state) {
+        case kIdle:
+            if (miso_size == 0) {
+                SwapBuffers();
+                if (miso_size == 0) {
+                    return kMisoIdleNibble;
+                }
+            }
+            miso_state = kLength;
+            return kMisoStartNibble;
+        case kLength:
+            // assert(miso_size > 0);
+            miso_state = kLength2;
+            return miso_size & 0xf;
+        case kLength2:
+            miso_nibbles_sent = 0;
+            miso_state = kData;
+            return miso_size >> 4;
+        case kData: {
+            uint8_t b = miso_buffer[miso_nibbles_sent / 2];
+            if (miso_nibbles_sent % 2 == 0) {
+                b &= 0xf;
+            } else {
+                b >>= 4;
+            }
+            miso_nibbles_sent += 1;
+            if (miso_nibbles_sent == miso_size * 2) {
+                SwapBuffers();
+                miso_state = kIdle;
+            }
+            return b;
+        }
+        }
+        __builtin_unreachable();
+    }
+};

arduino/kbd/parallel.cc

@@ -0,0 +1,95 @@
+#include "parallel.h"
+
+#include <stdint.h>
+
+#include "Arduino.h"
+
+namespace {
+
+constexpr int kParallelDataPins[] = {
+        D9, D8, D7, D6, D5, D4, D3, D2,
+};
+
+constexpr int kParallelBusyPin = D14;
+constexpr int kParallelAckPin = D15;
+constexpr int kParallelPaperoutPin = D12;
+constexpr int kParallelSelectPin = D11;
+
+constexpr int kParallelNibblePins[] = {
+        kParallelSelectPin,
+        kParallelPaperoutPin,
+        kParallelAckPin,
+        kParallelBusyPin,
+};
+
+constexpr bool kParallelNibbleInverted[] = {
+        false,
+        false,
+        false,
+        true,
+};
+
+constexpr int kParallelStrobePin = D10;
+
+volatile bool strobe_pending = false;
+volatile uint8_t strobe_byte = 0;
+
+void strobeIsr() {
+    strobe_pending = true;
+    strobe_byte = readParallel();
+}
+
+} // namespace
+
+uint8_t readParallel() {
+    uint8_t out = 0;
+    for (int i = 0; i < 8; i++) {
+        if (digitalReadFast(digitalPinToPinName(kParallelDataPins[i])) ==
+            HIGH) {
+            out |= (1 << i);
+        }
+    }
+    if (digitalReadFast(digitalPinToPinName(kParallelStrobePin)) == HIGH) {
+        out |= (1 << 8);
+    }
+    return out;
+}
+
+#define BIT(x, n) ((x & (1 << n)) ? HIGH : LOW)
+
+void writeParallel(uint8_t nibble) {
+    for (int i = 0; i < 4; i++) {
+        int lvl = BIT(nibble, i);
+        if (kParallelNibbleInverted[i]) {
+            lvl = lvl == HIGH ? LOW : HIGH;
+        }
+        digitalWriteFast(digitalPinToPinName(kParallelNibblePins[i]), lvl);
+    }
+}
+
+bool strobeOccurred(uint8_t &byte) {
+    bool pending;
+    {
+        noInterrupts();
+        pending = strobe_pending;
+        byte = strobe_byte;
+        strobe_pending = false;
+        interrupts();
+    }
+
+    return pending;
+}
+
+void setupParallel() {
+    for (int i = 0; i < sizeof(kParallelDataPins) / sizeof(int); i++) {
+        pinMode(kParallelDataPins[i], INPUT);
+    }
+    for (int i = 0; i < sizeof(kParallelNibblePins) / sizeof(int); i++) {
+        pinMode(kParallelNibblePins[i], OUTPUT);
+        digitalWrite(kParallelNibblePins[i], HIGH);
+    }
+    pinMode(kParallelStrobePin, INPUT);
+
+    attachInterrupt(digitalPinToInterrupt(kParallelStrobePin), strobeIsr,
+                    FALLING);
+}

arduino/kbd/parallel.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <stdint.h>
+
+/** Returns the byte present on D0~D7 */
+uint8_t readParallel();
+
+/** Writes a nibble on status pins */
+void writeParallel(uint8_t nibble);
+
+void setupParallel();
+
+/** Returns true and sets the byte if a strobe was received */
+bool strobeOccurred(uint8_t &byte);

bochsrc.txt

@@ -0,0 +1,5 @@
+romimage: file=$BXSHARE/BIOS-bochs-legacy
+boot:floppy
+floppya: 360k=polos.img, status=inserted
+display_library: sdl2
+keyboard: keymap=$BXSHARE/keymaps/sdl2-pc-us.map

crc16.c

@@ -1,35 +0,0 @@
-#include <stdint.h>
-
-#define kDataAddr ((uint8_t*) 0x0000)
-
-uint16_t crc16(int data_len) {
-    const uint8_t* data = kDataAddr;
-
-    uint16_t crc = 0xFFFF;
-    for (unsigned int i = 0; i < data_len; ++i) {
-        uint16_t dbyte = data[i];
-        crc ^= dbyte << 8;
-        for (unsigned char j = 0; j < 8; ++j) {
-            uint16_t mix = crc & 0x8000;
-            crc = (crc << 1);
-            if (mix)
-                crc = crc ^ 0x1021;
-        }
-    }
-    return crc;
-}
-
-asm (
-        ".global main      \n"
-        "main:             \n"
-        "  push %bp        \n"
-        "  mov %sp, %bp    \n"
-        "  mov 8(%bp), %si \n"
-        "  push (%si)      \n"
-        "  call crc16      \n"
-        "  add $0x2, %sp   \n"
-        "  mov 6(%bp), %di \n"
-        "  mov %ax, (%di)  \n"
-        "  pop %bp         \n"
-        "  lret $4         \n"
-        );

crc16.s

@@ -1,52 +0,0 @@
-	.arch i8086,jumps
-	.code16
-	.att_syntax prefix
-#NO_APP
-#APP
-	.global main      
-main:             
-  push %bp        
-  mov %sp, %bp    
-  mov 8(%bp), %si 
-  push (%si)      
-  call crc16      
-  add $0x2, %sp   
-  mov 6(%bp), %di 
-  mov %ax, (%di)  
-  pop %bp         
-  lret $4         
-
-#NO_APP
-	.text
-	.global	crc16
-	.type	crc16, @function
-crc16:
-	pushw	%bp
-	movw	%sp,	%bp
-	xorw	%bx,	%bx
-	movw	$-1,	%ax
-.L2:
-	cmpw	4(%bp),	%bx
-	jne	.L5
-	popw	%bp
-	ret
-.L5:
-	movb	%cs:(%bx),	%dl
-	movb	$8,	%cl
-	shlw	%cl,	%dx
-	xorw	%dx,	%ax
-	movb	%cl,	%dl
-.L4:
-	movw	%ax,	%cx
-	shlw	$1,	%cx
-	testw	%ax,	%ax
-	xchgw	%ax,	%cx
-	jge	.L3
-	xorw	$4129,	%ax
-.L3:
-	decb	%dl
-	jne	.L4
-	incw	%bx
-	jmp	.L2
-	.size	crc16, .-crc16
-	.ident	"GCC: (GNU) 6.3.0"

crt0.c

@@ -1,27 +0,0 @@
-#include <stdint.h>
-#include <string.h>
-
-int main();
-
-asm (
-        ".section .init     \n"
-        ".global _start     \n"
-        "_start:            \n\t"
-        "mov %cs, %ax       \n\t"
-        "mov %ax, %ds       \n\t"
-        "mov %ax, %es       \n\t"
-        "cli                \n\t"
-        "mov %ax, %ss       \n\t"
-        "mov $0x1000, %ax   \n\t"
-        "mov %ax, %sp       \n\t"
-        "sti                \n\t"
-        "jmp main"
-);
-
-void* memset(void* ptr, int val, size_t len) {
-    uint8_t* p = ptr;
-    while(len--) {
-        *p++ = val;
-    }
-    return ptr;
-}

fat12.c

@@ -1,138 +0,0 @@
-#include <stdint.h>
-#include <stdlib.h>
-
-#define kSectorsPerCluster 2
-#define kSectorsPerTrack 9
-#define kHeads 2
-#define kFatSizeSectors 2
-#define kRootDirSizeSectors 7
-#define kDataRegionStartSector (1 + kFatSizeSectors*2 + kRootDirSizeSectors)
-
-
-typedef struct {
-    char name[8];
-    char ext[3];
-    uint8_t attr;
-
-    uint8_t dontcare[14];
-
-    uint16_t cluster;
-    uint32_t size;
-} direntry;
-
-static uint8_t* gFat;
-static direntry* gRootdir;
-
-
-static int readsector(int c, int h, int s, uint8_t* addr) {
-    register uint8_t* dest asm ("bx") = addr;
-    register uint8_t nsects asm ("al") = 1;
-    register uint8_t func asm ("ah") = 0x02;
-    register uint8_t sect asm ("cl") = s;
-    register uint8_t cyl asm ("ch") = c;
-    register uint8_t head asm ("dh") = h;
-    register uint8_t drive asm ("dl") = 0;
-    register uint16_t seg asm ("es") = 0;
-
-    register uint8_t ret asm("ah");
-
-    for (int i = 0; i < 3; i++) {
-        asm volatile ("int $0x13"
-                : "=r" (ret)
-                : "r" (dest), "r" (nsects), "r" (func), "r" (sect),
-                  "r" (cyl), "r" (head), "r" (drive), "r" (seg));
-        if (ret == 0x80) {
-            continue;
-        } else {
-            return ret;
-        }
-    }
-
-    return ret;
-}
-
-static int readcluster(int cluster) {
-    int offs = cluster * 3 / 2;
-    if (cluster % 2) {
-        // high nibble is lsb + whole byte
-        return ((gFat[offs] & 0xf0) >> 4) + (gFat[offs+1] << 4);
-    } else {
-        return gFat[offs] + ((gFat[offs+1] & 0x0f) << 8);
-    }
-}
-
-static void cluster2chs(int cluster, int* c, int* h, int* s) {
-    int logicalsector = kDataRegionStartSector + (cluster - 2) * kSectorsPerCluster;
-    *s = (logicalsector % kSectorsPerTrack) + 1;
-    *h = (logicalsector / kSectorsPerTrack) % kHeads;
-    *c = logicalsector / (kHeads * kSectorsPerTrack);
-}
-
-static int strncmp(const char* s1, const char *s2, size_t len) {
-    for (int i = 0; i < len && s1[i]; i++) {
-        if (s1[i] != s2[i]) {
-            return 1;
-        }
-    }
-    // XXX: really we should return 0 only if *s1 == *s2 here too
-    return 0;
-}
-
-static int loadfile(direntry* entry, void* addr) {
-    int cluster = entry->cluster;
-    for (int i = 0; i < entry->size; i+=1024) {
-        int c, h, s;
-        cluster2chs(cluster, &c, &h, &s);
-        if (readsector(c, h, s, addr + i)) {
-            return -5;
-        }
-        s++;
-        if (s > 9) {
-            s = 1;
-            h++;
-        }
-        if (h > 1) {
-            h = 0;
-            c++;
-        }
-        if (readsector(c, h, s, addr + i + 512)) {
-            return -5;
-        };
-        cluster = readcluster(cluster);
-    }
-    return 0;
-}
-
-int fat12_init(void* fat_addr, void* rootdir_addr) {
-    if (readsector(0, 0, 2, fat_addr)) {
-        return -2;
-    }
-    if (readsector(0, 0, 6, rootdir_addr)) {
-        return -3;
-    }
-
-    gFat = fat_addr;
-    gRootdir = rootdir_addr;
-
-    return 0;
-}
-
-int fat12_readfile(const char* name, void* addr) {
-    direntry* file = 0;
-
-    for (int i = 0; i < 16; i++) {
-        direntry* entry = &gRootdir[i];
-        if (entry->name[0] == 0) {
-            break;
-        }
-        if (!strncmp(entry->name, name, 11)) {
-            file = entry;
-            break;
-        }
-    }
-    if (!file) {
-        return -4;
-    }
-
-    return loadfile(file, addr);
-}

fat12boot.c

@@ -1,59 +0,0 @@
-#include <stdint.h>
-#include <stdlib.h>
-
-#include "fat12.h"
-
-#define kPolmonAddress ((void*)0x0600)
-#define kFatAddress ((void*)0x1000)
-#define kRootDirAddress ((void*)0x1200)
-
-
-static int putchar(int c) {
-    register uint8_t khar asm ("al") = c;
-    register uint8_t func asm ("ah") = 0x0e;
-    register uint8_t page asm ("bh") = 0;
-
-    asm volatile ("int $0x10"
-            :: "r" (khar), "r" (func), "r" (page)
-            : "bp");
-
-    return c;
-}
-
-static int puts(const char* msg) {
-    while (*msg) {
-        putchar(*msg++);
-    }
-    return 0;
-}
-
-__attribute__((noreturn))
-static void die(const char* msg) {
-    puts(msg);
-    while (1) {
-    }
-    __builtin_unreachable();
-}
-
-__attribute__((noreturn))
-static void jump(void* addr) {
-    asm volatile ("ljmp $0,%0" :: "i"(addr));
-    __builtin_unreachable();
-}
-
-__attribute__((noreturn))
-static void loadpolmon() {
-    if (fat12_init(kFatAddress, kRootDirAddress)) {
-        die("fi");
-    }
-
-    if (fat12_readfile("POLMON  COM", kPolmonAddress)) {
-        die("pnf");
-    }
-
-    jump(kPolmonAddress);
-}
-
-int main() {
-    loadpolmon();
-}

ftpserve.py

@@ -0,0 +1,79 @@
+import argparse
+import logging
+import os
+import serial
+
+
+kCrc16Polynomial = 0x1021
+kCrc16Preset = 0xFFFF
+
+kDefaultSerialPort = None
+kDefaultBaudrate = 115200
+kDefaultChunkSize = 0x20
+
+logger = logging.getLogger(__name__)
+
+
+def crc16(data):
+    crc = kCrc16Preset
+    for c in data:
+        crc ^= c << 8
+        for j in range(8):
+            mix = crc & 0x8000
+            crc <<= 1
+            if mix:
+                crc ^= kCrc16Polynomial
+            crc &= 0xFFFF
+    return crc
+
+
+def getserial(port=None, baudrate=None, **kwargs):
+    if port is not None:
+        return serial.Serial(port, baudrate)
+
+    # return first /dev/ttyACMx found
+    for i in range(10):
+        try:
+            return serial.Serial(f"/dev/ttyACM{i}", baudrate)
+        except serial.SerialException:
+            pass
+    raise RuntimeError("No serial device available.")
+
+
+def ftpserve(file, device, chunksize=0x20):
+    with open(file, "rb") as f:
+        data = f.read()
+    device.reset_input_buffer()
+    logger.info(f"Serving file {file}")
+    for i in range(0, len(data), chunksize):
+        device.write(data[i : i + chunksize])
+        r = device.read()
+        if r != b"\x42":
+            raise RuntimeError(f"wrong response {r}")
+        logger.info(f"ack for chunk @{i}")
+    logger.info(f"Done serving file {file}")
+    crc = crc16(data)
+    logger.info(f"File length: {len(data):04x}, crc16: {crc:04x}")
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description="Serve a file to ftpget.")
+    parser.add_argument("file", help="file to serve")
+    parser.add_argument("--port", help="path to the serial port")
+    parser.add_argument("--baudrate", default=kDefaultBaudrate)
+    parser.add_argument("--chunksize", default=kDefaultChunkSize)
+    return parser.parse_args()
+
+
+def main():
+    logging.basicConfig(level=logging.INFO)
+    args = parse_args()
+    device = getserial(**vars(args))
+    ftpserve(args.file, device, args.chunksize)
+
+
+if __name__ == "__main__":
+    try:
+        main()
+    except KeyboardInterrupt:
+        pass

mrbridge.py

@@ -0,0 +1,67 @@
+import argparse
+import serial
+import threading
+import time
+import websocket
+
+kDefaultSerialPort = None
+kDefaultBaudrate = 115200
+
+
+def getserial(port=None, baudrate=None, **kwargs):
+    if port is not None:
+        return serial.Serial(port, baudrate)
+
+    # return first /dev/ttyACMx found
+    for i in range(10):
+        try:
+            return serial.Serial(f"/dev/ttyACM{i}", baudrate)
+        except serial.SerialException:
+            pass
+    raise RuntimeError("No serial device available.")
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description="Bridge a serial port to a websocket")
+    parser.add_argument(
+        "--port", help="path to the serial port", default=kDefaultSerialPort
+    )
+    parser.add_argument("--baudrate", default=kDefaultBaudrate)
+    parser.add_argument("ws", help="URL of the websocket")
+    return parser.parse_args()
+
+
+def device_thread(device, ws):
+    while True:
+        line = device.readline()
+        ws.send(line)
+
+
+def slowwrite(device, data):
+    for b in data:
+        device.write([b])
+        time.sleep(0.005)
+
+
+def ws_thread(device, ws):
+    while True:
+        data = ws.recv()
+        slowwrite(device, data.replace(b"\n", b"\r\n"))
+
+
+def main():
+    args = parse_args()
+    device = getserial(**vars(args))
+    ws = websocket.create_connection(args.ws)
+
+    wst = threading.Thread(target=ws_thread, args=(device, ws), daemon=True)
+    wst.start()
+
+    device_thread(device, ws)
+
+
+if __name__ == "__main__":
+    try:
+        main()
+    except KeyboardInterrupt:
+        pass

polmon.cc

@@ -1,386 +0,0 @@
-#include <cstdint>
-
-#ifndef WOZMON
-#define WOZMON 0
-#endif
-
-#if WOZMON
-#define BACKSPACE 0
-#define ASCIIDUMP 0
-#define CLEARSCREENCMD 0
-#define FARCALL 0
-#define SHOWTITLE 0
-#define BOOTSTRAP 0
-#endif  // WOZMON
-
-#ifndef BACKSPACE
-#define BACKSPACE 1
-#endif
-
-#ifndef ASCIIDUMP
-#define ASCIIDUMP 1
-#endif
-
-#ifndef CLEARSCREENCMD
-#define CLEARSCREENCMD 1
-#endif
-
-#ifndef FARCALL
-#define FARCALL 1
-#endif
-
-#ifndef SHOWTITLE
-#define SHOWTITLE 1
-#endif
-
-#ifndef BOOTSTRAP
-#define BOOTSTRAP 1
-#endif
-
-namespace {
-
-constexpr int kDumpSize = 16;
-
-uint8_t getc() {
-    register uint8_t c asm ("al");
-    asm volatile (
-            "movb $0x00, %%ah\n\t"
-            "int $0x16"
-            : "=r" (c)
-            :: "ah", "cc"
-            );
-    return c;
-}
-
-void putc(uint8_t c) {
-    asm volatile (
-            "push %%bp          \n\t"
-            "movb %0, %%al      \n\t"
-            "movb $0x0e, %%ah   \n\t"
-            "movb $0, %%bh      \n\t"
-            "int $0x10          \n\t"
-            "pop %%bp           \n\t"
-            :: "r" (c)
-            : "ax", "bh", "cc"
-            );
-}
-
-void puts(const char* s) {
-    while (*s) {
-        putc(*s++);
-    }
-}
-
-// arguments on the stack in reverse order
-extern "C" uint16_t Jump(uint16_t addr, int nargs);
-asm (
-        ".section .text         \n"
-        "Jump:                  \n"
-        "   push %bx            \n"
-        "   push %si            \n"
-        "   push %di            \n"
-        "   push %bp            \n"
-        "   push %es            \n"
-        "   push %ax            \n"  // addr
-        "   movw %sp, %bp       \n"
-        "   movw %dx, %si       \n"  // nargs
-        "   add %si, %si        \n"
-        "j0:                    \n"
-        "   test %si, %si       \n"
-        "   jz j1               \n"
-        "   lea 12(%bp,%si), %di\n"
-        "   push %di            \n"
-        "   sub $2, %si         \n"
-        "   jmp j0              \n"
-        "j1:                    \n"
-        "   lcall *(%bp)        \n"
-        "   add $4, %sp         \n"
-        "   pop %bp             \n"
-        "   pop %di             \n"
-        "   pop %si             \n"
-        "   pop %bx             \n"
-        "   ret"
-        // return value in ax
-        );
-
-constexpr uint8_t kBackspace = 0x7f;
-constexpr uint8_t kOtherBackspace = 0x08;
-
-uint8_t ReadHexNibble(uint8_t c) {
-    // lowercase only
-    if (c <= '9') {
-        return c - '0';
-    }
-    return 10 + (c - 'a');
-}
-
-uint16_t ReadUintN(int n, const char* buf) {
-    uint16_t out = 0;
-    for (int i = 0; i < n; i++) {
-        if (buf[i] == 0) {
-            break;
-        }
-        out <<= 4;
-        out += ReadHexNibble(buf[i]);
-    }
-    return out;
-}
-
-uint8_t ReadUint8(const char* buf) {
-    return ReadUintN(2, buf);
-}
-
-uint16_t ReadUint16(const char* buf) {
-    return ReadUintN(4, buf);
-}
-
-void WriteHexNibble(uint8_t c) {
-    if (c > 9) {
-        putc('a' + c - 10);
-    } else {
-        putc('0' + c);
-    }
-}
-
-void WriteUint8(uint8_t a) {
-    WriteHexNibble(a >> 4);
-    WriteHexNibble(a & 0xf);
-}
-
-void WriteUint16(uint16_t a) {
-    WriteUint8(a >> 8);
-    WriteUint8(a & 0xff);
-}
-
-void __set_es__(uint16_t es) {
-    asm volatile (
-            "mov %0, %%es"
-            :: "r" (es)
-            : "es"
-            );
-}
-
-uint8_t __get_es_u8__(uint16_t addr) {
-    register uint16_t ad asm ("di") = addr;
-    uint8_t ret;
-    asm volatile (
-            "movb %%es:(%1), %0"
-            : "=r" (ret)
-            : "r" (ad)
-            );
-    return ret;
-}
-
-void __set_es_u8__(uint16_t addr, uint8_t val) {
-    register uint16_t ad asm ("di") = addr;
-    asm volatile (
-            "movb %0, %%es:(%1)"
-            :: "ri" (val), "rmi" (ad)
-            : "memory"
-            );
-}
-
-__attribute__((noreturn))
-inline static void __basic__() {
-    asm volatile (
-            "movw $0x40, %ax    \n\t"
-            "mov %ax, %ds       \n\t"
-            "int $0x18"
-            );
-    __builtin_unreachable();
-}
-
-void Dump(uint16_t addr, int count) {
-    for (int i = 0; i < count; i++) {
-        putc(' ');
-        uint8_t d = __get_es_u8__(addr + i);
-        WriteUint8(d);
-    }
-#if ASCIIDUMP
-    putc(' ');
-    putc(' ');
-    for (int i = 0; i < count; i++) {
-        uint8_t d = __get_es_u8__(addr + i);
-        if (d > 31 && d < 127) {
-            putc(d);
-        } else {
-            putc('.');
-        }
-    }
-#endif
-}
-
-void DumpHex(uint16_t addr, uint16_t seg) {
-    addr &= -kDumpSize;
-
-    putc('[');
-    WriteUint16(seg);
-    putc(':');
-    __set_es__(seg);
-    WriteUint16(addr);
-    putc(']');
-    putc(':');
-    Dump(addr, kDumpSize);
-    putc('\r');
-    putc('\n');
-}
-
-void ClearScreen() {
-    asm volatile (
-            "movw $0x0002, %%ax  \n\t"
-            "int $0x10"
-            ::: "ax", "cc"
-            );
-}
-
-void Status(uint8_t status) {
-    asm volatile (
-            "xorb %%bh, %%bh    \n\t"
-            "movb $0x03, %%ah   \n\t"
-            "int $0x10          \n\t"
-            "mov %%dx, %%di     \n\t"
-            "movb $0x02, %%ah   \n\t"
-            "movw $77, %%dx     \n\t"
-            "int $0x10          \n\t"
-            "movb %0, %%al      \n\t"
-            "call _ZN12_GLOBAL__N_110WriteUint8Eh   \n\t"
-            "movb $0x02, %%ah   \n\t"
-            "movw %%di, %%dx    \n\t"
-            "int $0x10"
-            :: "rm" (status)
-            : "ax", "bh", "dx", "cx", "di", "cc"
-            );
-}
-
-bool ParseCommand(const char* buf, uint16_t& cur_addr, uint16_t& cur_seg) {
-    bool dump = true;
-    for (const char* ptr = buf; *ptr;) {
-        if (*ptr == 's') {
-            cur_addr = 0;
-            cur_seg = ReadUint16(ptr+1);
-            ptr += 5;
-        } else if (*ptr == '$') {
-            __basic__();
-        } else if (*ptr == 'r') {
-            dump = false;
-#if FARCALL
-            int nargs = 0;
-            ptr++;
-            for (; *ptr;) {
-                if (*ptr == ' ') {
-                    ptr++;
-                    continue;
-                }
-                uint16_t d = ReadUint16(ptr);
-                asm volatile ("push %0" :: "r" (d));
-                nargs++;
-                ptr += 4;
-            }
-            __set_es__(cur_seg);
-            uint16_t ret = Jump(cur_addr, nargs);
-            asm volatile (
-                    "shl %0   \n\t"
-                    "add %0, %%sp"
-                    :: "r"(nargs)
-                    );
-            WriteUint16(ret); 
-            putc('\r'); putc('\n');
-#else  // FARCALL
-            auto jump = reinterpret_cast<void(*)()>(cur_addr);
-            jump();
-#endif  // FARCALL
-            ptr++;
-#if CLEARSCREENCMD
-        } else if (*ptr == 'l') {
-            dump = false;
-            ClearScreen();
-            ptr++;
-#endif
-        } else if (*ptr == 'w') {
-            dump = false;
-            uint16_t addr = cur_addr;
-            ptr += 1;
-            for (; *ptr;) {
-                if (*ptr == ' ') {
-                    ptr++;
-                    continue;
-                }
-                uint8_t d = ReadUint8(ptr);
-                __set_es__(cur_seg);
-                __set_es_u8__(addr, d);
-                addr++;
-                ptr += 2;
-            }
-        } else {
-            cur_addr = ReadUint16(ptr);
-            ptr += 4;
-        }
-    }
-    return dump;
-}
-
-const char* prompt = "> ";
-
-void polmon() {
-    uint16_t cur_addr = 0;
-    uint16_t cur_seg = 0;
-    char inbuf[64];
-    bool first = true;
-    char* inptr = inbuf;
-
-    ClearScreen();
-#if SHOWTITLE    
-    puts("PolMon 0.2\r\n");
-#endif  // SHOWTITLE
-    puts(prompt);
-
-    while (1) {
-        uint8_t c = getc();
-        putc(c);  // echo
-        if (c == '\r') {
-            *inptr = 0;
-            if (inbuf[0] == 0) {
-                if (!first) {
-                    cur_addr += kDumpSize;
-                }
-            } else {
-                putc('\n');
-            }
-
-            if (ParseCommand(inbuf, cur_addr, cur_seg)) {
-                DumpHex(cur_addr, cur_seg);
-            };
-            first = false;
-            inptr = inbuf;
-            puts(prompt);
-#if BACKSPACE
-        } else if (c == kBackspace || c == kOtherBackspace) {
-            inptr--;
-            if (inptr < inbuf) {
-                inptr = inbuf;
-                putc(' ');
-                continue;
-            }
-            putc(' ');
-            putc(kOtherBackspace);
-#endif
-        } else {
-            *inptr = c;
-            inptr++;
-        }
-    }
-}
-
-}  // namespace
-
-int main() {
-    polmon();
-}
-
-#if BOOTSTRAP
-__attribute__((section(".init"), noreturn, used))
-void _start() {
-    main();
-    __builtin_unreachable();
-}
-#endif  // BOOTSTRAP

src/Makefile

@@ -0,0 +1,55 @@
+CC = ia16-elf-gcc
+CXX = ia16-elf-gcc
+LD = ia16-elf-gcc
+OBJCOPY = ia16-elf-objcopy
+CXXFLAGS = -mregparmcall -ffunction-sections -Os -flto
+CFLAGS = -mregparmcall -ffunction-sections -Os -flto
+LDFLAGS = -mregparmcall -Wl,--gc-sections -Os -nostdlib -flto
+
+%.bin: %.asm
+	nasm $< -o $@
+
+%.elf:
+	$(LD) $(LDFLAGS) $(CPPFLAGS) -o $@ $^
+
+%.com: %.elf
+	$(OBJCOPY) -O binary $< $@
+
+fat12boot.bin:
+	$(OBJCOPY) -O binary $< $@
+
+fat12boot.elf: fat12boot.o fat12.o bootsect.S stdlib.o
+fat12boot.elf: LDFLAGS += -T bootsect.ld
+
+fat12boot.bin: fat12boot.elf
+
+stdlib.o: CFLAGS := $(filter-out -flto, $(CFLAGS))
+
+polmon.elf: LDFLAGS += -T init.ld
+polmon.elf: polmon.o stdlib.o
+
+polio.elf: LDFLAGS += -T flat0600.ld -mprotected-mode
+polio.elf: polio-main.o polio.s fat12.o paracomm.o stdlib.o
+
+paracli.elf: LDFLAGS += -T doscom.ld
+paracli.elf: paracli.s paracomm.o
+
+dos-programs = mushroom.com hello.com ftpget.com crc16.com
+$(dos-programs:.com=.elf): LDFLAGS += -T doscom.ld
+
+mushroom.elf: mushroom.s
+hello.elf: hello.o stdlib.o crt0.s
+ftpget.elf: ftpget.o stdlib.o crt0.s
+crc16.elf: crc16.o stdlib.o crt0.s
+
+polos.img: fat12boot.bin polmon.com polio.com $(dos-programs)
+	dd if=/dev/zero of=$@ bs=512 count=720
+	mformat -i $@ -t 40 -h 2 -s 9
+	mcopy -i $@ polio.com ::/
+	mcopy -i $@ polmon.com ::/
+	mcopy -i $@ $(dos-programs) ::/
+	dd if=fat12boot.bin of=$@ conv=notrunc
+
+.PHONY: clean
+clean:			## Remove generated files
+	rm -rf *.bin *.elf *.o *.com polos.img

src/bootsect.S

@@ -5,7 +5,7 @@
 .global _start
 _start:
 #ifndef NOBPB
-    jmp l0
+    jmp 0f
     nop
 
 .ascii "IBM  3.1"
@@ -18,7 +18,7 @@ bpb_localsectors:    .word 720
 bpb_mediadescr:      .byte 0xfd
 bpb_sectsperfat:     .word 2
 
-l0:
+0:
 #endif  // NOBPB
     cli
     xor %ax, %ax

src/bootsect.ld

@@ -0,0 +1,25 @@
+SECTIONS {
+    . = 0x7c00;
+
+    .text : {
+        KEEP(*(.init))
+        *(.text*)
+    }
+
+    .rodata : {
+        *(.rodata*)
+    }
+
+    .bss (NOLOAD) : {
+        * (.bss)
+    }
+
+    .data (NOLOAD) : {
+        *(.data)
+    }
+
+    . = 0x7dfe;
+    .magic : {
+        SHORT(0xAA55);
+    }
+}

src/call.asm

@@ -19,15 +19,15 @@ _start:
     mov bx, 0x6
     xor cx, cx
 a1:
-    cmp cx, [es:si+4]
+    cmp cx, [si+4]
     jge a2
-    lea ax, [es:si+bx]
+    lea ax, [si+bx]
     push ax
     add bl, 2
     inc cl
     jmp a1
 a2:
-    call far [es:si]
+    call far [si]
     pop bp
     pop di
     pop si

src/copy.asm

@@ -11,9 +11,12 @@ main:
     mov si, [si]
     push ds
     push es
-    pop ds
+    mov ax, cs
+    mov ds, ax
+    mov es, ax
     cld
     rep movsw
+    pop es
     pop ds
 
     retf 6

src/crc16.asm

@@ -0,0 +1,45 @@
+CPU 8086
+
+_start:
+    push bp
+    mov bp, sp
+    mov si, [bp+8]
+    push word [si]
+    mov si, [bp+10]
+    push word [si]
+    call crc16
+    mov di, [bp+6]
+    mov [di], ax
+    mov sp, bp
+    pop bp
+    retf 6
+
+crc16:
+	push	bp
+	mov	bp, sp
+	mov	bx, [bp+4]
+    add [bp+6], bx
+	mov	ax, -1
+.L2:
+	cmp	bx, [bp+6]
+	jne	.L5
+	pop	bp
+	ret
+.L5:
+	mov	dl, [bx]
+	mov	cl, 0x8
+	shl	dx, cl
+	xor ax, dx
+	mov dl, cl
+.L4:
+	mov	cx, ax
+	shl	cx, 1
+	test ax, ax
+	xchg	cx, ax
+	jge	.L3
+	xor	ax, 4129
+.L3:
+	dec	dl
+	jne	.L4
+	inc	bx
+	jmp	.L2

src/crc16.c

@@ -0,0 +1,31 @@
+#include <stdint.h>
+
+#include "polos.h"
+
+#define kDefaultSegment 0
+
+uint16_t crc16(uint16_t data, const uint16_t seg, int data_len) {
+    uint16_t crc = 0xFFFF;
+    for (unsigned int i = 0; i < data_len; ++i) {
+        uint16_t dbyte = __get_far_u8__(data + i, seg);
+        crc ^= dbyte << 8;
+        for (unsigned char j = 0; j < 8; ++j) {
+            uint16_t mix = crc & 0x8000;
+            crc = (crc << 1);
+            if (mix)
+                crc = crc ^ 0x1021;
+        }
+    }
+    return crc;
+}
+
+int main(int argc, int argv[]) {
+    if (argc < 2) {
+        return -1;
+    }
+    uint16_t seg = kDefaultSegment;
+    if (argc > 2) {
+        seg = argv[2];
+    }
+    return crc16(argv[0], seg, argv[1]);
+}

src/crt0.s

@@ -0,0 +1,8 @@
+    .arch i8086,jumps
+    .code16
+    .intel_syntax noprefix
+
+    .section .init
+    .global _start
+_start:
+    jmp main

src/doscom.ld

@@ -1,5 +1,5 @@
 SECTIONS {
-    . = 0x7c00;
+    . = 0x100;
 
     .text : {
         KEEP(*(.init))
@@ -14,7 +14,7 @@ SECTIONS {
         * (.bss)
     }
 
-    .data : {
+    .data (NOLOAD) : {
         *(.data)
     }
 }

src/fat12.c

@@ -0,0 +1,239 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "polos.h"
+
+#define kSectorsPerCluster 2
+#define kSectorsPerTrack 9
+#define kHeads 2
+#define kTracks 40
+#define kFatSizeSectors 2
+#define kRootDirSizeSectors 7
+#define kBytesPerCluster 1024
+#define kDataRegionStartSector (1 + kFatSizeSectors * 2 + kRootDirSizeSectors)
+#define kNumClusters ((kSectorsPerTrack * kHeads * kTracks - kDataRegionStartSector) / kSectorsPerCluster + 2)
+
+typedef struct {
+    char name[8];
+    char ext[3];
+    uint8_t attr;
+
+    uint8_t dontcare[14];
+
+    uint16_t cluster;
+    uint32_t size;
+} direntry;
+
+static uint8_t* gFat;
+static direntry* gRootdir;
+
+static uint8_t rwsector(uint8_t w, int c, int h, int s, void* addr) {
+    uint16_t ret;
+    uint16_t cmd = w ? 0x0301 : 0x0201;
+    // retry for a total of up to 3 attempts if drive not ready
+    for (int i = 0; i < 3; i++) {
+        ret = __readwritesector__(cmd, addr, c, h, s) >> 8;
+        if (ret != 0x80) {
+            break;
+        }
+    }
+
+    return ret;
+}
+
+static uint8_t readsector(int c, int h, int s, void* addr) {
+    return rwsector(0, c, h, s, addr);
+}
+
+static uint8_t writesector(int c, int h, int s, void* addr) {
+    return rwsector(1, c, h, s, addr);
+}
+
+static int readcluster(int cluster) {
+    int offs = cluster * 3 / 2;
+    if (cluster % 2) {
+        // high nibble is lsb + whole byte
+        return ((gFat[offs] & 0xf0) >> 4) + (gFat[offs + 1] << 4);
+    } else {
+        return gFat[offs] + ((gFat[offs + 1] & 0x0f) << 8);
+    }
+}
+
+static int writecluster(int cluster, int value) {
+    int offs = cluster * 3 / 2;
+    if (cluster % 2) {
+        gFat[offs] = (gFat[offs] & 0x0f) + ((value & 0x0f) << 4);
+        gFat[offs+1] = value >> 4;
+        // high nibble is lsb + whole byte
+    } else {
+        gFat[offs] = value & 0xff;
+        gFat[offs+1] = (gFat[offs+1] & 0xf0) + (value >> 8);
+    }
+    return value;
+}
+
+static int firstfreecluster() {
+    for (int i = 2; i < kNumClusters; i++) {
+        if (readcluster(i) == 0) {
+            return i;
+        }
+    }
+    return -1;
+}
+
+static void cluster2chs(int cluster, int* c, int* h, int* s) {
+    int logicalsector =
+            kDataRegionStartSector + (cluster - 2) * kSectorsPerCluster;
+    *s = (logicalsector % kSectorsPerTrack) + 1;
+    *h = (logicalsector / kSectorsPerTrack) % kHeads;
+    *c = logicalsector / (kHeads * kSectorsPerTrack);
+}
+
+static int loadfile(direntry* entry, void* addr) {
+    int cluster = entry->cluster;
+    for (int i = 0; i < entry->size; i += kBytesPerCluster) {
+        int c, h, s;
+        cluster2chs(cluster, &c, &h, &s);
+        if (readsector(c, h, s, addr + i)) {
+            return -5;
+        }
+        s++;
+        if (s > 9) {
+            s = 1;
+            h++;
+        }
+        // if (h > 1) {  // this will never happen
+        //     h = 0;
+        //     c++;
+        // }
+        if (readsector(c, h, s, addr + i + 512)) {
+            return -5;
+        };
+        cluster = readcluster(cluster);
+    }
+    return 0;
+}
+
+static direntry* findfile(const char* name) {
+    direntry* file = 0;
+
+    for (int i = 0; i < 16; i++) {
+        direntry* entry = &gRootdir[i];
+        if (!strncmp(entry->name, name, 11)) {
+            file = entry;
+            break;
+        }
+    }
+    return file;
+}
+
+static direntry* newfile(const char* name) {
+    direntry* file = 0;
+
+    for (int i = 0; i < 16; i++) {
+        direntry* entry = &gRootdir[i];
+        if (entry->name[0] == 0) {
+            file = entry;
+            break;
+        }
+    }
+    if (!file) {
+        return file;
+    }
+
+    memcpy(file->name, name, 11);
+    file->size = 0;
+    file->cluster = 0;
+
+    return file;
+}
+
+static int allocatecluster(int previous) {
+    int cluster = firstfreecluster();
+    writecluster(cluster, 0xfff);
+    if (previous != 0) {
+        writecluster(previous, cluster);
+    }
+    return cluster;
+}
+
+static void freeclusterchain(int cluster) {
+    if (cluster < 2 || cluster >= 0xf00) {
+        return;
+    }
+    freeclusterchain(readcluster(cluster));
+    writecluster(cluster, 0);
+}
+
+static int savefile(direntry* file, void* addr, int size) {
+    freeclusterchain(file->cluster);
+    file->cluster = 0;
+    int cluster = 0;
+    for (int i = 0; i < size; i += kBytesPerCluster) {
+        cluster = allocatecluster(cluster);
+        if (file->cluster == 0) {
+            file->cluster = cluster;
+        }
+        int c, h, s;
+        cluster2chs(cluster, &c, &h, &s);
+        if (writesector(c, h, s, addr + i)) {
+            return -7;
+        }
+        s++;
+        if (s > 9) {
+            s = 1;
+            h++;
+        }
+        // if (h > 1) {  // no cluster will cross a cylinder boundary
+        //     h = 0;
+        //     c++;
+        // }
+        if (writesector(c, h, s, addr + i + 512)) {
+            return -7;
+        };
+    }
+    file->size = size;
+    if (writesector(0, 0, 2, gFat)) {
+        return -8;
+    }
+    if (writesector(0, 0, 6, gRootdir)) {
+        return -9;
+    }
+    return 0;
+}
+
+int fat12_init(void* fat_addr, void* rootdir_addr) {
+    if (readsector(0, 0, 2, fat_addr)) {
+        return -2;
+    }
+    if (readsector(0, 0, 6, rootdir_addr)) {
+        return -3;
+    }
+
+    gFat = fat_addr;
+    gRootdir = rootdir_addr;
+
+    return 0;
+}
+
+int fat12_readfile(const char* name, void* addr) {
+    direntry* file = findfile(name);
+    if (!file) {
+        return -4;
+    }
+
+    return loadfile(file, addr);
+}
+
+int fat12_writefile(const char* name, void* addr, int size) {
+    direntry* file = findfile(name);
+    if (!file) {
+        file = newfile(name);
+    }
+    if (!file) {
+        // no moar space
+        return -6;
+    }
+    return savefile(file, addr, size);
+}

src/fat12boot.c

@@ -0,0 +1,53 @@
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "fat12.h"
+
+#define kPolmonAddress ((void*)0x0600)
+#define kFatAddress ((void*)0x1000)
+#define kRootDirAddress ((void*)0x1200)
+
+static int putchar(int c) {
+    register uint8_t khar asm("al") = c;
+    register uint8_t func asm("ah") = 0x0e;
+    register uint8_t page asm("bh") = 0;
+
+    asm volatile("int $0x10" ::"r"(khar), "r"(func), "r"(page) : "bp");
+
+    return c;
+}
+
+static int puts(const char* msg) {
+    while (*msg) {
+        putchar(*msg++);
+    }
+    return 0;
+}
+
+__attribute__((noreturn)) static void die(const char* msg) {
+    puts(msg);
+    while (1) {
+    }
+    __builtin_unreachable();
+}
+
+__attribute__((noreturn)) static void jump(void* addr) {
+    asm volatile("ljmp $0,%0" ::"i"(addr));
+    __builtin_unreachable();
+}
+
+__attribute__((noreturn)) static void loadpolmon() {
+    if (fat12_init(kFatAddress, kRootDirAddress)) {
+        die("fi");
+    }
+
+    while (fat12_readfile("POLIO   COM", kPolmonAddress)) {
+        asm volatile("mov $00, %%ah      \n\t"
+                     "int $0x16          \n\t" ::
+                             : "ax");
+    }
+
+    jump(kPolmonAddress);
+}
+
+int main() { loadpolmon(); }

src/flat0600.ld

@@ -14,7 +14,7 @@ SECTIONS {
         * (.bss)
     }
 
-    .data : {
+    .data (NOLOAD) : {
         *(.data)
     }
 }

src/ftp.asm

@@ -0,0 +1,48 @@
+CPU 8086
+
+chunksize equ 0x20
+devicedelay equ 0x08
+
+_start:
+    push bp
+    mov bp, sp
+    sub sp, 8
+    mov [bp-2], word chunksize ; recv size
+    mov [bp-4], word 0xf000 ; recv addr
+    mov [bp-6], word 0x0001 ; send size
+    mov [bp-8], word 0x7000 ; send addr
+    mov bx, [bp-8]
+    mov [bx], byte 0x42
+l0:
+    cmp word [bp-4], 0xf600
+    jb l1
+l2:
+    mov sp, bp
+    pop bp
+    ret
+l1:
+    mov ah, 0x07
+    int 0x80
+    test al, al
+    jnz l1
+    push word [bp-2]
+    push word [bp-4]
+    mov ah, 0x05
+    int 0x80
+    test al, al
+    jz l2
+    mov ah, 0
+    add [bp-4], ax
+    push word [bp-6]
+    push word [bp-8]
+    mov ah, 0x06
+    int 0x80
+    add sp, 8
+    mov cx, devicedelay
+l3: 
+    mov ah, 0x07
+    push cx
+    int 0x80
+    pop cx
+    loop l3             ; give the device some time to answer
+    jmp l0

src/ftpget.c

@@ -0,0 +1,52 @@
+#include <stdint.h>
+#include <unistd.h>
+
+#include "polos.h"
+
+#define kDefaultChunkSize 0x20
+
+static int recv(uint8_t* buf, uint8_t size) {
+    uint16_t ds = 0;
+    asm volatile ("push %%ds    \n\t"
+            "mov %0, %%ds \n\t"
+            "pop %0       \n" : "+r"(ds));
+    int len = read(kLpt1, buf, size);
+    asm volatile ("mov %0, %%ds" :: "r"(ds));
+    return len;
+}
+
+int main(int argc, uint16_t argv[]) {
+    if (argc < 2) {
+        return -1;
+    }
+
+    uint8_t* dest = (uint8_t*)argv[0];
+    uint16_t size = argv[1];
+    uint8_t chunksize = kDefaultChunkSize;
+    if (argc > 2) {
+        chunksize = argv[2];
+    }
+
+    uint8_t ack = 0x42;
+    int i;
+
+    for (i = 0; i < size;) {
+        // delay?
+
+        int len;
+        for (int j = 0; j < 3; j++) {
+            int r = runcomms(kUntilIdle);
+            len = recv(dest + i, chunksize);
+            if (len > 0) {
+                break;
+            }
+        }
+        if (len <= 0) {
+            break;
+        }
+        write(kLpt1, &ack, 1);
+        i += len;
+    }
+
+    return i;
+}

src/hello.c

@@ -0,0 +1,12 @@
+#include <stdio.h>
+
+int main(int argc, int argv[]) {
+    puts("Hello, world!\r\n");
+
+    if (argc > 1) {
+        return argv[0] + argv[1];
+    } else if (argc > 0) {
+        return argv[0];
+    }
+    return 0x42;
+}

src/init.ld

@@ -0,0 +1,20 @@
+SECTIONS {
+    . = 0x1200;
+
+    .text : {
+        KEEP(*(.init))
+        *(.text*)
+    }
+
+    .rodata : {
+        *(.rodata*)
+    }
+
+    .bss (NOLOAD) : {
+        * (.bss)
+    }
+
+    .data (NOLOAD) : {
+        *(.data)
+    }
+}

src/mushroom.s

@@ -0,0 +1,261 @@
+    .arch i8086,jumps
+    .code16
+    .intel_syntax noprefix
+
+    .section .init
+    .global _start
+_start:
+    mov ax, cs
+    mov ds, ax
+    mov es, ax
+    cli
+    mov ss, ax
+    mov sp, 0x100
+    sti
+    jmp main
+
+    .section .bss
+kBufSize = 77
+kDividerRow = 23
+kRecvBufSize = 128
+
+curpos: .word 0
+inputsize: .byte 0
+escaped: .byte 0
+inputbuf: .zero kBufSize
+recvbuf: .zero kRecvBufSize
+
+    # XXX: funky call
+    # inputs:
+    #   si: string offset
+    #   cl: string length
+    # clobbers: ax, bh, dx
+    .section .text.printn
+printn:
+    push bx
+    push bp
+    mov bh, 0
+1:
+    test cl, cl
+    jz 0f
+    mov al, [si]
+    cmpb escaped, 0
+    je 3f
+    cmp al, 'm'
+    jne 5f
+    movb escaped, 0
+    jmp 5f
+3:
+    cmp al, 0x1b        # ESC
+    jne 4f
+    movb escaped, 1
+    jmp 5f
+4:
+    mov ah, 0x0e        # write tty
+    int 0x10
+    push cx
+    mov ah, 0x03        # get cursor
+    int 0x10
+    cmp dh, kDividerRow
+    jb 2f
+    push dx
+    mov ah, 0x08        # read color
+    int 0x10
+    mov bh, ah
+    xor cx, cx
+    mov dx, 0x164f
+    mov ax, 0x0601      # scroll up, 1 line
+    int 0x10
+    pop dx
+    dec dh
+    mov bh, 0
+    mov ah, 0x02        # set cursor
+    int 0x10
+2:
+    pop cx
+5:
+    inc si
+    dec cl
+    jmp 1b
+0:
+    pop bp
+    pop bx
+    ret
+
+    # XXX: funky call
+    # inputs:
+    #   si: string offset
+    #   cl: string length
+    # clobbers: ax, bh, dx
+    .section .text.addtext
+addtext:
+    push di
+    push cx
+    mov bh, 0
+    mov ah, 0x03            # get cursor pos
+    int 0x10
+    pop cx
+    push dx
+    mov di, offset curpos
+    mov dx, [di]
+    mov ah, 0x02            # set cursor
+    int 0x10
+    call printn
+    mov ah, 0x03            # get cursor pos
+    int 0x10
+    mov [di], dx
+    pop dx
+    mov ah, 0x02            # set cursor
+    int 0x10
+    pop di
+    ret
+
+    .section .text.sendbuffer
+sendbuffer:
+    push bp
+    mov bp, sp
+    sub sp, 2
+    mov al, inputsize
+    mov [bp-2], al
+    movb inputsize, 0
+    mov si, offset .l0
+    mov cl, 2
+    call addtext
+    mov si, offset inputbuf
+    mov cl, [bp-2]
+    call addtext
+    mov si, offset .l1
+    mov cl, 2
+    call addtext
+    mov si, offset inputbuf
+    mov cl, [bp-2]
+    call parasend
+    # XXX: should check cx in case not everything was sent
+    mov al, ' '
+    mov dx, 0x1802      # [24; 2]
+    call drawchar
+    mov ah, 0x02 
+    int 0x10            # mov cursor back to start of line
+    add sp, 2
+    pop bp
+    ret
+
+    # draw until end of line
+    # al: char
+    # dh: row
+    # dl: start col
+    .section .text.drawchar
+drawchar:
+    push ax
+    mov bh, 0
+    mov ah, 0x02    # set cursor
+    int 0x10
+    mov cx, 80
+    sub cl, dl
+    pop ax
+    mov ah, 0x0a
+    int 0x10
+    ret
+
+    .section .text.parasend
+parasend:
+    mov ah, 0x06        # send parallel
+    push cx
+    push si
+    int 0x80
+    mov cx, 1
+    push cx
+    mov cx, offset .l1 + 1
+    push cx
+    mov ah, 0x06        # send parallel
+    int 0x80
+    add sp, 8
+    ret
+    
+prompt:
+    mov bh, 0
+    mov dx, 0x1800
+    mov ah, 0x02
+    int 0x10
+    mov ah, 0x0e
+    mov al, '>'
+    int 0x10
+    mov ah, 0x0e
+    mov al, ' '
+    int 0x10
+    ret
+
+    .section .rodata
+.l0: .ascii "> "
+.l1: .byte 0x0d, 0x0a
+.l2: .ascii "MUSHRoom 8086 client 0.1\r\n"
+l2len = . - offset .l2
+
+    .section .text.main
+    .global main
+main:
+    movb inputsize, 0       # inputsize = 0
+    movw curpos, 0          # mov buffer cursor to [0;0]
+    movb escaped, 0
+    mov ax, 0x0002
+    int 0x10
+    mov si, offset .l2
+    mov cl, l2len
+    call addtext
+    mov dx, 0x1700          # [23; 0]
+    mov al, 0xc4            # horizontal box line
+    call drawchar
+    call prompt
+0:
+    mov ah, 0x01
+    int 0x16                # check buffer
+    jz 1f                   # if empty, do a round of comms
+    mov ah, 0x00
+    int 0x16                # read 1 key
+    cmp al, 0x08            # backspace
+    je 5f
+    cmp al, 0x0d            # CR
+    je 4f
+    mov di, offset inputbuf        
+    mov si, offset inputsize
+    mov bh, 0
+    mov bl, [si]
+    cmp bl, kBufSize        # stop accepting input at end of screen
+    jge 1f                  # do a round of comms
+    mov [di+bx], al         # store character in buffer
+    incb [si]               # increment buffer size
+    mov ah, 0x0e
+    mov bh, 0
+    int 0x10                # local echo
+    jmp 0b
+5:
+    mov bl, inputsize
+    test bl, bl
+    jz 0b
+    decb inputsize
+    mov bh, 0
+    mov ah, 0x0e
+    int 0x10                # backspace
+    mov ax, 0x0e20
+    int 0x10
+    mov ax, 0x0e08
+    int 0x10
+    jmp 0b
+4:
+    call sendbuffer         # send input buffer
+1:
+    mov ax, 0x0700          # do parallel comms
+    int 0x80
+    mov ax, kRecvBufSize
+    push ax
+    mov ax, offset recvbuf
+    push ax
+    mov ah, 0x05            # recv
+    int 0x80
+    test al, al
+    mov cl, al
+    pop si
+    pop bx
+    jz 0b
+    call addtext
+    jmp 0b

src/paracli.s

@@ -0,0 +1,80 @@
+    .arch i8086,jumps
+    .code16
+    .intel_syntax noprefix
+
+    .section .init
+    .global _start
+_start:
+    mov ax, cs
+    mov ds, ax
+    mov es, ax
+    cli
+    mov ss, ax
+    mov sp, 0x100
+    sti
+    jmp main
+
+    .section .text.parcb
+parcb:
+    push bx
+    push si
+    push bp
+    mov si, ax
+1:
+    test dx, dx
+    jz 0f
+    mov al, [si]
+    mov ah, 0x0e
+    mov bh, 0
+    int 0x10
+    dec dx
+    inc si
+    jmp 1b
+0:
+    pop bp
+    pop si
+    pop bx
+    ret
+
+    .section .rodata.l0
+.l0: .ascii "> "
+.l1: .ascii "."
+
+delay = 500
+
+    .section .text.main
+    .global main
+main:
+    mov ax, 0x0002
+    int 0x10
+    mov ax, offset parcb
+    call paracomm_init
+0:
+    mov ah, 0x01
+    int 0x16
+    jz 1f
+    mov ah, 0x00
+    int 0x16
+    mov ah, 0
+    call paracomm_send
+    test ax, ax
+    jz 0b
+1:
+    call paracomm_nextbyte
+    mov dx, 0x3bc
+    out dx, al
+    add dl, 2
+    mov al, 1
+    out dx, al
+    mov cx, delay
+2:  loop 2b    
+    mov al, 0
+    out dx, al
+    mov cx, delay
+3:  loop 3b    
+    dec dl
+    in al, dx
+    mov cl, 4
+    shr al, cl
+    call paracomm_feed
+    jmp 0b

src/paracomm.c

@@ -0,0 +1,125 @@
+#include "paracomm.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+#define kMosiIdleByte 0x00
+#define kMosiStartByte 0x42
+#define kMisoIdleNibble 0x0
+#define kMisoStartNibble 0xa
+
+static uint8_t mosi_workbuf[2][256];
+static uint8_t mosi_workbuf_idx;
+static uint8_t mosi_workbuf_size;
+
+static uint8_t* mosi_sendbuf;
+static uint8_t mosi_size;
+static uint8_t mosi_sent;
+
+static uint8_t mosi_state;
+
+static uint8_t miso_recvbuf[256];
+static uint8_t miso_size;
+static uint8_t miso_received_nibbles;
+static uint8_t miso_state;
+recv_cb miso_recv_cb;
+
+static void swapbuffers() {
+    mosi_sendbuf = mosi_workbuf[mosi_workbuf_idx];
+    mosi_size = mosi_workbuf_size;
+
+    mosi_workbuf_size = 0;
+    mosi_workbuf_idx = (mosi_workbuf_idx + 1) % 2;
+}
+
+uint8_t paracomm_nextbyte() {
+    switch (mosi_state) {
+    case 0:
+        if (mosi_size == 0) {
+            swapbuffers();
+            if (mosi_size == 0) {
+                return kMosiIdleByte;
+            }
+        }
+        mosi_state = 1;
+        return kMosiStartByte;
+    case 1:
+        // assert(mosi_size > 0)
+        mosi_sent = 0;
+        mosi_state = 2;
+        return mosi_size;
+    case 2: {
+        uint8_t b = mosi_sendbuf[mosi_sent];
+        mosi_sent += 1;
+
+        if (mosi_sent == mosi_size) {
+            swapbuffers();
+            mosi_state = 0;
+        }
+
+        return b;
+    }
+    }
+
+    __builtin_unreachable();
+}
+
+void paracomm_feed(uint8_t n) {
+    switch (miso_state) {
+    case 0:
+        if (n == kMisoStartNibble) {
+            miso_state = 1;
+        } else if (n == kMisoIdleNibble) {
+        } else {
+            // error: spurious nibble
+        }
+        break;
+    case 1:
+        miso_size = n;
+        miso_state = 2;
+        break;
+    case 2:
+        miso_size += n << 4;
+        miso_received_nibbles = 0;
+        miso_state = 3;
+        break;
+    case 3: {
+        uint8_t idx = miso_received_nibbles / 2;
+        if (miso_received_nibbles % 2 == 0) {
+            miso_recvbuf[idx] = n;
+        } else {
+            miso_recvbuf[idx] += n << 4;
+        }
+        miso_received_nibbles += 1;
+
+        if (miso_received_nibbles == 2 * miso_size) {
+            miso_recv_cb(miso_recvbuf, miso_size);
+            miso_state = 0;
+        }
+    } break;
+    }
+}
+
+void paracomm_init(recv_cb miso_cb) {
+    mosi_size = 0;
+    mosi_workbuf_idx = 0;
+    mosi_workbuf_size = 0;
+    mosi_state = 0;
+
+    miso_state = 0;
+    miso_recv_cb = miso_cb;
+}
+
+int paracomm_send(uint8_t b) {
+    if (mosi_workbuf_size == 256) {
+        return -1;
+    }
+
+    uint8_t* buff = mosi_workbuf[mosi_workbuf_idx];
+    buff[mosi_workbuf_size] = b;
+    mosi_workbuf_size += 1;
+
+    return 0;
+}
+
+uint8_t paracomm_busy() { return mosi_state != 0 || miso_state != 0; }

src/paracomm.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <stdint.h>
+
+typedef void (*recv_cb)(const uint8_t* buf, uint8_t size);
+
+/** Must call first **/
+void paracomm_init(recv_cb cb);
+
+/** Sends a single byte.
+ * Returns: 0 if no error, non-0 otherwise.
+ */
+int paracomm_send(uint8_t b);
+
+/** Call after reading a nibble from the port */
+void paracomm_feed(uint8_t n);
+
+/** Yields the next byte to send out the port */
+uint8_t paracomm_nextbyte();
+
+/** Returns non-zero if busy */
+uint8_t paracomm_busy();

src/polio-main.c

@@ -0,0 +1,112 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "fat12.h"
+#include "paracomm.h"
+
+#define kFatAddr ((void*)0x1a00)
+#define kRootDirAddr ((void*)0x1c00)
+#define kPolmonAddr ((void*)0x1200)
+#define kInt80Vector ((uint16_t*)(0x80 * 4))
+#define kParallelDataPort 0x3bc
+#define kParallelStatusPort 0x3bd
+#define kParallelControlPort 0x3be
+#define kParaDelay 100
+#define kRecvBufferSize 256
+
+void dosdbt();
+void int80h();
+
+static uint8_t parabuf[kRecvBufferSize];
+static uint8_t parasize;
+
+static void paracb(const uint8_t* buf, uint8_t size) {
+    if (parasize + size > sizeof(parabuf)) {
+        size = sizeof(parabuf) - parasize;
+    }
+    memcpy(parabuf + parasize, buf, size);
+    parasize += size;
+}
+
+static void die() {
+    while (1) {
+    }
+}
+
+static void __outb__(uint16_t port, uint8_t data) {
+    register uint16_t p asm("dx") = port;
+    register uint8_t d asm("al") = data;
+    asm volatile("outb %0, %1" ::"r"(d), "r"(p));
+}
+
+static uint8_t __inb__(uint16_t port) {
+    register uint16_t p asm("dx") = port;
+    register uint8_t d asm("al");
+    asm volatile("inb %1, %0" : "=r"(d) : "r"(p));
+    return d;
+}
+
+static void __delay__(int n) {
+    for (int i = 0; i < n; i++) {
+        asm volatile("");
+    }
+}
+
+uint16_t xferpara(uint8_t until_idle) {
+    do {
+        uint8_t mosib = paracomm_nextbyte();
+        __outb__(kParallelDataPort, mosib);
+        __outb__(kParallelControlPort, 1);
+        __delay__(kParaDelay);
+        __outb__(kParallelControlPort, 0);
+        uint8_t mison = __inb__(kParallelStatusPort) >> 4;
+        paracomm_feed(mison);
+    } while (until_idle && paracomm_busy());
+
+    return paracomm_busy();
+}
+
+uint16_t parasend(uint8_t* addr, uint8_t size) {
+    uint8_t i;
+    for (i = 0; i < size; i++) {
+        if (paracomm_send(addr[i])) {
+            break;
+        }
+    }
+    return i;
+}
+
+uint16_t pararecv(uint8_t* buf, uint8_t size) {
+    if (parasize == 0) {
+        return 0;
+    }
+    if (size > parasize) {
+        size = parasize;
+    }
+    memcpy(buf, parabuf, size);
+    if (size < parasize) {
+        memcpy(parabuf, parabuf + size, parasize - size);
+    }
+    parasize -= size;
+
+    return size;
+}
+
+int main() {
+    dosdbt();
+    parasize = 0;
+    paracomm_init(paracb);
+
+    fat12_init(kFatAddr, kRootDirAddr);
+
+    uint16_t* int80v = kInt80Vector;
+    int80v[0] = (uint16_t)int80h;
+    int80v[1] = 0;
+
+    if (fat12_readfile("POLMON  COM", kPolmonAddr)) {
+        die();
+    }
+
+    asm volatile("jmp *%0" ::"r"(kPolmonAddr));
+}

src/polio.s

@@ -0,0 +1,191 @@
+    .arch i8086,jumps
+    .code16
+    .intel_syntax noprefix
+
+    .section .init
+    .global _start
+_start:
+    cli
+    mov ax, 0x2000      # stack address, shared with polmon
+    mov sp, ax          # ss should already be 0
+    sti
+    jmp main
+
+
+diskpointer = 0x1e*4
+dbtbase = 0x0500
+
+    .section .text.dosdbt
+    .global dosdbt
+dosdbt:                    # assumes es=0
+    push si
+    push di
+    push ds
+    mov si, diskpointer
+    lds si, [si]
+    mov di, dbtbase
+    mov cx, 0x0a           # size of the dbt
+    cld
+    rep movsb              # move dbt to dbtbase
+    pop ds
+    mov al, 9              # sectors per track
+    mov si, dbtbase
+    mov [si+4], al         # set number of sectors
+    mov di, diskpointer
+    mov [di], si           # new int1eh offset
+    mov [di+2], ds         # and segment
+    pop di
+    pop si
+    ret
+
+    .section .text.int80stuff
+
+## floppy stuff
+
+# same as read but with a different int13h:ah value
+writesector:
+    mov ax, 0x0301      # write command, 1 sector
+    jmp 0f
+
+# params: addr, c, h, s
+# return status in ah, sectors read (1 or 0) in al
+readsector:
+    mov ax, 0x0201      # read command, 1 sector
+0:
+    mov bx, [bp+0]      # addr
+    mov ch, [bp+2]      # c
+    mov dh, [bp+4]      # h
+    mov cl, [bp+6]      # s
+    mov dl, 0           # drive
+    int 0x13
+    ret
+
+
+# params: c, h
+# returns: status in ah, 0 in al?
+
+buffer = 0xe000         # buffer needs to be big enough for a whole track
+                        # (for some reason), so 9 * 512 bytes = 0x1200 bytes
+sectors = 9
+
+formattrack:
+    mov bx, buffer
+    xor cx, cx
+0:
+    cmp cl, sectors
+    jnl 1f
+    mov di, cx
+    and di, 0x0f        # max 15 sectors
+    shl di, 1
+    shl di, 1           # di = cl*4
+    lea di, [bx+di]
+    mov al, [bp+0]      # track number
+    mov [di+0], al
+    mov al, [bp+2]      # head number
+    mov [di+1], al
+    mov al, cl          # sector number
+    inc al
+    mov [di+2], al
+    movb [di+3], 0x02   # 512 bytes per sector
+    inc cl
+    jmp 0b
+1:
+    mov ah, 0x05        # format track
+    mov al, sectors
+    mov dl, 0           # first drive
+    mov ch, [bp+0]      # track number
+    mov dh, [bp+2]      # head number
+    mov cl, 1           # sector number (first sector?)
+    int 0x13
+    ret
+
+# params: ds:fname, ds:dest
+readfile:
+    mov si, [bp-14] # ds
+    mov cl, 4
+    shl si, cl
+    mov ax, [bp+0]
+    add ax, si
+    mov dx, [bp+2]
+    add dx, si
+    jmp fat12_readfile
+
+# params: ds:fname, ds:src, size
+writefile:
+    mov si, [bp-14] # ds
+    mov cl, 4
+    shl si, cl
+    mov ax, [bp+0]
+    add ax, si
+    mov dx, [bp+2]
+    add dx, si
+    mov cx, [bp+4]
+    jmp fat12_writefile
+
+# params: ds:addr, size
+sendpara:
+    mov si, [bp-14] # ds
+    mov cl, 4
+    shl si, cl
+    mov ax, [bp+0]
+    add ax, si
+    mov dx, [bp+2]
+    jmp parasend
+
+# params: ds:addr, size
+recvpara:
+    mov si, [bp-14] # ds
+    mov cl, 4
+    shl si, cl
+    mov ax, [bp+0]
+    add ax, si
+    mov dx, [bp+2]
+    jmp pararecv
+
+dummy:
+    mov ax, -1
+    ret
+
+    .section .text.int80h
+    .global int80h
+int80h:
+    push si
+    push di
+    push bp
+    push ds
+    push es
+    mov bp, sp
+    xor cx, cx
+    mov es, cx
+    mov ds, cx
+    xchg ah, cl
+    shl cl
+    cmp cl, offset int80h_entries
+    jge 0f
+    mov si, cx
+    add bp, 16       # 10 for us, 6 for the interrupt
+    call cs:[int80h_table+si]
+    jmp 1f
+0:
+    mov ax, -1
+1:
+    pop es
+    pop ds
+    pop bp
+    pop di
+    pop si
+    iret
+
+    .section .rodata.int80h
+int80h_table:
+    .word offset dummy          # 0x00
+    .word offset readsector     # 0x01
+    .word offset writesector    # 0x02
+    .word offset formattrack    # 0x03
+    .word offset readfile       # 0x04
+    .word offset recvpara       # 0x05
+    .word offset sendpara       # 0x06
+    .word offset xferpara       # 0x07
+    .word offset writefile      # 0x08
+
+int80h_entries = . - int80h_table

src/polmon.cc

@@ -0,0 +1,417 @@
+#include <cstdint>
+#include <cstdio>
+#include <cstring>
+
+#include "polos.h"
+
+namespace {
+
+constexpr int kDumpSize = 16;
+
+extern "C" uint16_t Int80h(uint16_t fun, uint16_t nargs, uint16_t args[]);
+asm(".section .text.Int80h  \n"
+    "Int80h:                \n"
+    "   push %si            \n"
+    "   push %bp            \n"
+    "   mov %sp, %bp        \n"
+    "   mov %cx, %si        \n"
+    "   shl $1, %dx         \n"
+    "   add %dx, %si        \n"
+    "0:                     \n"
+    "   cmp %cx, %si        \n"
+    "   je 1f               \n"
+    "   push -2(%si)        \n"
+    "   sub $2, %si         \n"
+    "   jmp 0b              \n"
+    "1:                     \n"
+    "   int $0x80           \n"
+    "   mov %bp, %sp        \n"
+    "   pop %bp             \n"
+    "   pop %si             \n"
+    "   ret"
+    // return value in ax
+);
+
+constexpr uint8_t kBackspace = 0x7f;
+constexpr uint8_t kOtherBackspace = 0x08;
+
+uint8_t ReadHexNibble(uint8_t c) {
+    // lowercase only
+    if (c <= '9') {
+        return c - '0';
+    }
+    return 10 + (c - 'a');
+}
+
+uint16_t ReadUintN(int n, const char*& buf) {
+    uint16_t out = 0;
+    for (int i = 0; i < n; i++) {
+        if (*buf < '0') {
+            break;
+        }
+        out <<= 4;
+        out += ReadHexNibble(*buf);
+        buf += 1;
+    }
+    return out;
+}
+
+uint8_t ReadUint8(const char*& buf) { return ReadUintN(2, buf); }
+
+uint16_t ReadUint16(const char*& buf) { return ReadUintN(4, buf); }
+
+void WriteHexNibble(uint8_t c) {
+    if (c > 9) {
+        putchar('a' + c - 10);
+    } else {
+        putchar('0' + c);
+    }
+}
+
+void WriteUint8(uint8_t a) {
+    WriteHexNibble(a >> 4);
+    WriteHexNibble(a & 0xf);
+}
+
+void WriteUint16(uint16_t a) {
+    WriteUint8(a >> 8);
+    WriteUint8(a & 0xff);
+}
+
+void WriteUint16ln(uint16_t a) {
+    WriteUint16(a);
+    puts("\r\n");
+}
+
+__attribute__((noreturn)) inline static void __basic__() {
+    asm volatile("movw $0x40, %ax    \n\t"
+                 "mov %ax, %ds       \n\t"
+                 "int $0x18");
+    __builtin_unreachable();
+}
+
+void Dump(uint16_t addr, uint16_t seg, int count) {
+    for (int i = 0; i < count; i++) {
+        putchar(' ');
+        uint8_t d = __get_far_u8__(addr + i, seg);
+        WriteUint8(d);
+    }
+    putchar(' ');
+    putchar(' ');
+    for (int i = 0; i < count; i++) {
+        uint8_t d = __get_far_u8__(addr + i, seg);
+        if (d > 31 && d < 127) {
+            putchar(d);
+        } else {
+            putchar('.');
+        }
+    }
+}
+
+void DumpHex(uint16_t addr, uint16_t seg) {
+    addr &= -kDumpSize;
+
+    putchar('[');
+    WriteUint16(seg);
+    putchar(':');
+    WriteUint16(addr);
+    putchar(']');
+    putchar(':');
+    Dump(addr, seg, kDumpSize);
+    puts("\r\n");
+}
+
+void ClearScreen() {
+    asm volatile("movw $0x0002, %%ax  \n\t"
+                 "int $0x10" ::
+                         : "ax", "cc");
+}
+
+char toupper(char c) {
+    if (c >= 'a' && c <= 'z') {
+        return c - ('a' - 'A');
+    }
+    return c;
+}
+
+void tofatname(const char* name, uint8_t len, char* fatname) {
+    int j = 0;
+    for (int i = 0; i < 11; i++) {
+        if (j == len || name[j] == '.') {
+            fatname[i] = ' ';
+        } else {
+            fatname[i] = toupper(name[j]);
+            j++;
+        }
+        if (i == 7 && name[j] == '.') {
+            j++;
+        }
+    }
+}
+
+uint16_t __readfile__(const char* name, uint16_t addr) {
+    register uint16_t ret asm("ax");
+    asm volatile("push %2        \n\t"
+                 "push %1        \n\t"
+                 "mov $04, %%ah  \n\t"
+                 "int $0x80      \n\t"
+                 "pop %%cx       \n\t"
+                 "pop %%cx       \n\t"
+                 : "=r"(ret)
+                 : "r"(name), "r"(addr)
+                 : "bx", "cx", "dx", "memory", "cc");
+
+    return ret;
+}
+
+uint16_t LoadFile(const char* name, uint8_t len, uint16_t seg) {
+    constexpr uint16_t kAddress = 0x100;
+    // trampoline:
+    //      call 0x100
+    //      retf
+    // XXX: if you change kAddress, the trampoline needs to be updated
+    constexpr uint8_t kTrampoline[] = {0xe8, 0xfd, 0x00, 0xcb};
+
+    uint16_t headeraddr = (seg << 4);
+    uint16_t flataddr = headeraddr + kAddress;
+
+    char fatname[11];
+    tofatname(name, len, fatname);
+
+    uint16_t r = __readfile__(fatname, flataddr);
+    if (r) {
+        memcpy(fatname + 8, "COM", 3);
+        r = __readfile__(fatname, flataddr);
+    }
+    if (r) {
+        return r;
+    }
+
+    auto* ptr = reinterpret_cast<uint8_t*>(headeraddr);
+    memcpy(ptr, kTrampoline, sizeof(kTrampoline));
+
+    return 0;
+}
+
+uint16_t Exec(uint16_t seg, uint8_t argc, uint16_t* argv) {
+    constexpr uint16_t kAddress = 0x100;
+    constexpr uint16_t kArgvAddress = 0x0004;
+
+    uint16_t headeraddr = (seg << 4);
+    auto* argp = reinterpret_cast<uint16_t*>(headeraddr + kArgvAddress);
+    memcpy(argp, argv, argc * 2);
+
+    register uint16_t ac asm("ax") = argc;
+    register uint16_t av asm("dx") = kArgvAddress;
+    asm volatile("mov %2, %%cx      \n\t"
+                 "mov %%cx, %%ds    \n\t"
+                 "mov %%cx, %%es    \n\t"
+                 "cli               \n\t"
+                 "mov %%cx, %%ss    \n\t"
+                 "mov %3, %%cx      \n\t"
+                 "xchg %%cx, %%sp   \n\t"
+                 "sti               \n\t"
+                 "push %%cx         \n\t"
+                 "push %2           \n\t"
+                 "xor %%cx, %%cx    \n\t"
+                 "push %%cx         \n\t"
+                 "mov %%sp, %%bx    \n\t"
+                 "lcall *(%%bx)     \n\t"
+                 "pop %%cx          \n\t"
+                 "pop %%dx          \n\t"
+                 "mov %%cx, %%ds    \n\t"
+                 "mov %%cx, %%es    \n\t"
+                 "cli               \n\t"
+                 "pop %%sp          \n\t"
+                 "mov %%cx, %%ss    \n\t"
+                 "sti"
+                 : "+r"(ac), "+r"(av)
+                 : "r"(seg), "i"(kAddress)
+                 : "bx", "cx", "memory", "cc");
+
+    return ac;
+}
+
+constexpr uint16_t kCtrlBreakVector = (0x1b * 4);
+
+extern "C" void cbreak();
+asm("   .section .text.cbreak   \n"
+    "cbreak:                \n"
+    "   xor %ax, %ax        \n"
+    "   mov %ax, %ds        \n"
+    "   cli                 \n"
+    "   mov %ax, %ss        \n"
+    "   mov $0x2000, %sp    \n"
+    "   sti                 \n"
+    "   pushf               \n"
+    "   push %ax            \n"
+    "   mov $0x1000, %ax    \n"
+    "   push %ax            \n"
+    "   mov $0x20, %al      \n"
+    "   out %al, $0x20      \n"
+    "   iret                \n");
+
+void InstallCtrlBreak() {
+    auto vec = reinterpret_cast<void (**)()>(kCtrlBreakVector);
+    vec[0] = cbreak;
+    vec[1] = 0;
+}
+
+// j
+// w [u8]*
+// i [u16] [u16]*
+// r str [u16]*
+// k u16 u16 u16
+
+int ReadArgs(const char*& ptr, uint16_t* args, int size) {
+    int nargs = 0;
+    while (*ptr && nargs < size) {
+        if (*ptr == ' ') {
+            ptr += 1;
+            continue;
+        }
+        args[nargs] = ReadUint16(ptr);
+        nargs += 1;
+    }
+    return nargs;
+}
+
+int ReadString(const char*& ptr, const char*& str) {
+    while (*ptr == ' ') {
+        ptr++;
+    }
+    str = ptr;
+    int l;
+    for (l = 0; *ptr && *ptr != ' '; l++, ptr++) {
+    }
+    return l;
+}
+
+bool ParseCommand(const char* buf, uint16_t& cur_addr, uint16_t& cur_seg) {
+    bool dump = true;
+    for (const char* ptr = buf; *ptr;) {
+        if (*ptr == 's') {
+            ptr += 1;
+            cur_addr = 0;
+            ReadArgs(ptr, &cur_seg, 1);
+        } else if (*ptr == '$') {
+            __basic__();
+        } else if (*ptr == 'j') {
+            dump = false;
+            ptr++;
+            auto jump = reinterpret_cast<uint16_t (*)()>(cur_addr);
+            uint16_t ret = jump();
+            WriteUint16ln(ret);
+        } else if (*ptr == 'i') {
+            dump = false;
+            ptr++;
+            uint16_t args[8];  // ought to be enough for everybody
+            int nargs = ReadArgs(ptr, args, 8);
+            uint16_t fun = args[0];
+            uint16_t ret = Int80h(fun, nargs - 1, args + 1);
+            WriteUint16ln(ret);
+        } else if (*ptr == 'l') {
+            dump = false;
+            ptr++;
+            const char* fname;
+            int l = ReadString(ptr, fname);
+            uint16_t ret = LoadFile(fname, l, cur_seg);
+            if (ret) {
+                WriteUint16ln(ret);
+            }
+        } else if (*ptr == 'r') {
+            dump = false;
+            ptr++;
+            uint16_t args[8];  // ought to be enough for everybody
+            int nargs = ReadArgs(ptr, args, 8);
+            uint16_t ret = Exec(cur_seg, nargs, args);
+            WriteUint16ln(ret);
+        } else if (*ptr == 'w') {
+            dump = false;
+            uint16_t addr = cur_addr;
+            ptr += 1;
+            for (; *ptr;) {
+                if (*ptr == ' ') {
+                    ptr++;
+                    continue;
+                }
+                uint8_t d = ReadUint8(ptr);
+                __set_far_u8__(addr, cur_seg, d);
+                addr++;
+            }
+        } else if (*ptr == 'k') {
+            dump = false;
+            ptr++;
+            uint16_t args[2];
+            // TODO: implement copy on non-zero segments
+            if (cur_seg == 0 && ReadArgs(ptr, args, 2) == 2) {
+                auto* src = reinterpret_cast<uint8_t*>(args[0]);
+                uint16_t size = args[1];
+                auto* dest = reinterpret_cast<uint8_t*>(cur_addr);
+                memcpy(dest, src, size);
+            }
+        } else {
+            cur_addr = ReadUint16(ptr);
+        }
+    }
+    return dump;
+}
+
+void DisplayPrompt() { puts("> "); }
+
+[[noreturn]]
+void polmon() {
+    uint16_t cur_addr = 0;
+    uint16_t cur_seg = 0;
+    char inbuf[64];
+    bool first = true;
+    char* inptr = inbuf;
+
+    ClearScreen();
+    puts("PolMon for Workgroups 3.1\r\n");
+    DisplayPrompt();
+
+    while (1) {
+        uint8_t c = getchar();
+        putchar(c);  // echo
+        if (c == '\r') {
+            *inptr = 0;
+            if (inbuf[0] == 0) {
+                if (!first) {
+                    cur_addr += kDumpSize;
+                }
+            } else {
+                putchar('\n');
+            }
+
+            if (ParseCommand(inbuf, cur_addr, cur_seg)) {
+                DumpHex(cur_addr, cur_seg);
+            };
+            first = false;
+            inptr = inbuf;
+            DisplayPrompt();
+        } else if (c == kBackspace || c == kOtherBackspace) {
+            inptr--;
+            if (inptr < inbuf) {
+                inptr = inbuf;
+                putchar(' ');
+                continue;
+            }
+            putchar(' ');
+            putchar(kOtherBackspace);
+        } else {
+            *inptr = c;
+            inptr++;
+        }
+    }
+    __builtin_unreachable();
+}
+
+}  // namespace
+
+int main() {
+    InstallCtrlBreak();
+    polmon();
+}
+
+__attribute__((section(".init"), used)) void _start() { main(); }

src/polos.h

@@ -0,0 +1,59 @@
+#pragma once
+
+#include <stdint.h>
+
+#define kLpt1 0x10
+#define kUntilIdle 1
+#define kOnce 0
+
+int runcomms(char until_idle);
+
+int putchar(int);
+int puts(const char*);
+
+inline static uint8_t __get_far_u8__(uint16_t addr, uint16_t seg) {
+    register uint16_t ad asm("di") = addr;
+    register uint8_t ret asm("al");
+    asm("mov %2, %%es              \t\n"
+        "movb %%es:(%%di), %%al    \t\n"
+        : "=r"(ret)
+        : "r"(ad), "r"(seg)
+        : "es");
+    return ret;
+}
+
+inline static void __set_far_u8__(uint16_t addr, uint16_t seg, uint8_t val) {
+    register uint16_t ad asm("di") = addr;
+    register uint8_t v asm("al") = val;
+    asm("mov %0, %%es              \t\n"
+    "stosb      \n\t" ::"r"(seg), "r"(ad), "r"(v) : "es", "memory");
+}
+
+inline static uint16_t __readwritesector__(uint16_t cmd, uint8_t* addr, uint8_t c, uint8_t h, uint8_t s) {
+    register uint8_t* dest asm("bx") = addr;
+    register uint8_t sect asm("cl") = s;
+    register uint8_t cyl asm("ch") = c;
+    register uint8_t head asm("dh") = h;
+    register uint8_t drive asm("dl") = 0;
+    register uint16_t ret asm("ax");
+
+    asm volatile("xor %%ax, %%ax \n\t"
+            "mov %%ax, %%es \n\t"
+            "mov %1, %%ax \n\t"
+            "int $0x13"
+            : "=r"(ret)
+            : "ir"(cmd), "r"(dest), "r"(sect), "r"(cyl),
+            "r"(head), "r"(drive)
+            );
+
+    return ret;
+}
+
+inline static uint16_t __readsector__(uint8_t* addr, uint8_t c, uint8_t h, uint8_t s) {
+    return __readwritesector__(0x0201, addr, c, h, s);
+}
+
+inline static uint16_t __writesector__(uint8_t* addr, uint8_t c, uint8_t h, uint8_t s) {
+    return __readwritesector__(0x0301, addr, c, h, s);
+}
+

src/readio.asm

@@ -0,0 +1,10 @@
+BITS 16
+CPU 8086
+
+_start:
+    mov bp, sp
+    mov si, [bp+4]
+    mov dx, [si]
+    xor ax, ax
+    in al, dx
+    retf 2

src/runcomm.asm

@@ -0,0 +1,10 @@
+CPU 8086
+
+mov cx, 0x100
+a:
+    mov ah, 0x07
+    int 0x80
+    test al, al
+    loopnz a
+b:
+    ret

src/stdlib.c

@@ -0,0 +1,100 @@
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "polos.h"
+
+int getchar() {
+    register char c asm("al");
+    asm volatile("movb $0x00, %%ah\n\t"
+                 "int $0x16"
+                 : "=r"(c)::"ah", "cc");
+    return c;
+}
+
+int putchar(int c) {
+    asm volatile("push %%bp          \n\t"
+                 "mov %0, %%ax      \n\t"
+                 "movb $0x0e, %%ah   \n\t"
+                 "movb $0, %%bh      \n\t"
+                 "int $0x10          \n\t"
+                 "pop %%bp           \n\t" ::"r"(c)
+                 : "ax", "bh", "cc");
+    return 0;
+}
+
+int puts(const char* s) {
+    while (*s) {
+        putchar(*s++);
+    }
+    return 0;
+}
+
+void* memcpy(void* dest, const void* src, size_t n) {
+    uint8_t* d = dest;
+    const uint8_t* s = src;
+    for (int i = 0; i < n; i++) {
+        d[i] = s[i];
+    }
+    return dest;
+}
+
+void* memset(void* ptr, int val, size_t len) {
+    uint8_t* p = ptr;
+    while (len--) {
+        *p++ = val;
+    }
+    return ptr;
+}
+
+int strncmp(const char* s1, const char* s2, size_t len) {
+    for (int i = 0; i < len && s1[i]; i++) {
+        if (s1[i] != s2[i]) {
+            return 1;
+        }
+    }
+    // XXX: really we should return 0 only if *s1 == *s2 here too
+    return 0;
+}
+
+static int int80h_2(uint8_t fun, uint16_t arg1, uint16_t arg2) {
+    register uint16_t a1 asm("dx") = arg1;
+    register uint16_t a2 asm("cx") = arg2;
+    register uint8_t ah asm("ah") = fun;
+    register uint16_t ret asm("ax");
+    asm volatile("push %3            \n\t"
+                 "push %2            \n\t"
+                 "int $0x80          \n\t"
+                 "pop %%cx           \n\t"
+                 "pop %%cx           \n\t"
+                 : "=r"(ret)
+                 : "r"(ah), "r"(a1), "r"(a2)
+                 : "bx", "cc", "memory");
+
+    return ret;
+}
+
+int runcomms(char until_idle) {
+    register int ret asm("ax");
+    register char ui asm("al") = until_idle;
+    asm volatile("mov $0x07, %%ah    \n\t"
+                 "int $0x80          \n\t"
+                 : "=r"(ret)
+                 : "r"(ui)
+                 : "bx", "cx", "dx", "cc", "memory");
+
+    return ret;
+}
+
+int read(int fd, void* buf, size_t size) {
+    if (fd != kLpt1) {
+        return -1;
+    }
+    return int80h_2(0x05, (uint16_t)buf, size);
+}
+
+int write(int fd, void* buf, size_t size) {
+    if (fd != kLpt1) {
+        return -1;
+    }
+    return int80h_2(0x06, (uint16_t)buf, size);
+}

src/trampoline.asm

@@ -0,0 +1,13 @@
+CPU 8086
+
+src equ 0xf000
+dest equ 0x0600
+size equ 0x0600
+
+_start:
+    mov cx, size
+    mov si, src
+    mov di, dest
+    rep movsb
+    mov ax, dest
+    jmp ax

src/writeio.asm

@@ -0,0 +1,12 @@
+BITS 16
+CPU 8086
+
+_start:
+    mov bp, sp
+    mov si, [bp+6]
+    mov dx, [si]
+    xor ax, ax
+    mov si, [bp+4]
+    mov al, [si]
+    out dx, al
+    retf 4