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.

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

Useful stuff

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