From dd5d329dff65786bd5aa90cb4dccbd4cdab4d031 Mon Sep 17 00:00:00 2001
From: Paul Mathieu <paul@ponteilla.net>
Date: Mon, 29 Sep 2025 17:57:42 +0200
Subject: [PATCH] Refactor boot with polio.com first, then polmon

---
 Makefile    |   6 +-
 flat1000.ld |  20 ++++++
 polio.s     | 189 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 213 insertions(+), 2 deletions(-)
 create mode 100644 flat1000.ld
 create mode 100644 polio.s

diff --git a/Makefile b/Makefile
index f48a8ec..68fb208 100644
--- a/Makefile
+++ b/Makefile
@@ -34,6 +34,8 @@ fat12boot.bin: fat12boot.elf
 polmon.elf: LDFLAGS += -T flat1000.ld
 polmon.elf: polmon.o stdlib.o
 
+polio.elf: LDFLAGS += -T flat0600.ld
+polio.elf: polio.s fat12.o
 
 wozmon.o: polmon.cc
 wozmon.o: CPPFLAGS = -DWOZMON=1
@@ -49,8 +51,8 @@ wozmon.bin: wozmon.elf
 polos.img: fat12boot.bin polmon.com polio.com
 	dd if=/dev/zero of=$@ bs=512 count=720
 	mformat -i $@ -t 40 -h 2 -s 9
-	mcopy -i $@ polio.com ::/polio.com
-	mcopy -i $@ polmon.com ::/polmon.com
+	mcopy -i $@ polio.com ::/
+	mcopy -i $@ polmon.com ::/
 	dd if=fat12boot.bin of=$@ conv=notrunc
 
 .PHONY: clean
diff --git a/flat1000.ld b/flat1000.ld
new file mode 100644
index 0000000..cfd4329
--- /dev/null
+++ b/flat1000.ld
@@ -0,0 +1,20 @@
+SECTIONS {
+    . = 0x1000;
+
+    .text : {
+        KEEP(*(.init))
+        *(.text*)
+    }
+
+    .rodata : {
+        *(.rodata*)
+    }
+
+    .bss (NOLOAD) : {
+        * (.bss)
+    }
+
+    .data : {
+        *(.data)
+    }
+}
diff --git a/polio.s b/polio.s
new file mode 100644
index 0000000..95e4045
--- /dev/null
+++ b/polio.s
@@ -0,0 +1,189 @@
+    .arch i8086,jumps
+    .code16
+    .intel_syntax noprefix
+
+    .section .init
+    .global _start
+_start:
+    jmp main
+
+
+diskpointer = 0x1e*4
+dbtbase = 0x0500
+
+    .section .text.dosdbt
+    .local 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
+
+# near copy [param 2] bytes, es:[param 0] -> es:[param 1]
+copy:
+    mov si, [bp+0]      # source
+    mov di, [bp+2]      # destination
+    mov cx, [bp+4]      # length
+    cld
+    rep movsb
+    ret
+
+## 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
+    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
+
+
+readfile:
+    mov ax, [bp+0]
+    mov dx, [bp+2]
+    call fat12_readfile
+    ret
+
+
+    .section .rodata.polmon_str
+polmon_str: .ascii "POLMON  COM"
+polmon_addr = 0x1000
+
+    .section .text.main
+    .global main
+main:
+    cli
+    mov ax, 0x2000      # stack address
+    mov sp, ax          # ss should already be 0
+    sti
+    call dosdbt
+    mov ax, 0x1a00      # first sector of first fat
+    mov dx, 0x1c00      # first sector of root dir
+    call fat12_init
+
+    mov si, 0x80*4
+    movw [si], offset int80h
+    movw [si+2], 0
+
+    mov ax, offset polmon_str 
+    mov dx, polmon_addr
+    call fat12_readfile
+    test ax, ax
+    jnz 0f
+
+    jmp polmon_addr
+0:
+    mov ax, 0x0e42
+    mov bh, 0
+    int 0x10
+    cli
+    hlt
+
+    .section .text.int80h
+int80h:
+    push bx
+    push si
+    push di
+    push bp
+    push ds
+    push es
+    xor cx, cx
+    mov es, cx
+    mov ds, cx
+    shl ah
+    cmp ah, offset int80h_entries
+    jge 0f
+    mov al, ah
+    xor ah, ah
+    mov si, ax
+    mov bp, sp
+    lea bp, [bp + 18]       # 12 for us, 6 for the interrupt
+    call [int80h_table+si]
+    jmp 1f
+0:
+    mov ax, -1
+1:
+    pop es
+    pop ds
+    pop bp
+    pop di
+    pop si
+    pop bx
+    iret
+
+
+    .section .rodata.int80h
+int80h_table:
+    .word offset copy           # 0x00
+    .word offset readsector     # 0x01
+    .word offset writesector    # 0x02
+    .word offset formattrack    # 0x03
+    .word offset readfile       # 0x04
+
+int80h_entries = . - int80h_table