PoC

kprintf.asm

@@ -0,0 +1,140 @@
+; important functions in this file: kprintf
+
+; write a character to kernel output
+; in: al
+kputc:
+  push ax ; dont destroy ah
+  push dx
+  mov ah,0x02 ; DOS putc
+  mov dl,al
+  int 0x21
+  pop dx
+  pop ax
+  ret
+
+; write a string to kernel output
+; in: ds:di
+kputs:
+  push ax
+.loop:
+  lodsb
+  cmp al,0x00
+  je .end
+  call kputc
+  jmp .loop
+.end:
+  pop ax
+  ret
+
+; prints a nibble in hex
+; in: al
+kprint4:
+  and al, 0x0F
+  add al, 0x30
+  cmp al, 0x3a
+  jl kputc
+  add al, 0x07
+  jmp kputc
+
+; print a byte
+; in: al
+kprint8:
+  push ax ; avoid destroying ah
+  aam 16 ; high nibble moved into ah
+  xchg ah,al ; high nibble first
+  call kprint4
+  xchg ah,al
+  call kprint4
+  pop ax
+  ret
+
+; print a word
+; in: ax
+kprint16:
+  xchg ah,al
+  call kprint8
+  xchg ah,al
+  call kprint8
+  ret
+
+; read a word from the stack, using bp as stack pointer
+; in: bp
+; out: ax, bp
+kprintf_lodsw:
+  push ds ; work segment for lodsw
+  push si ; work pointer for lodsw
+  push ss ; data transfer to ds
+  pop ds
+  mov si,bp
+  lodsw
+  mov bp,si ; write back incremented value
+  pop si
+  pop ds
+  ret
+
+; print data from stack
+; in: ds:si, ss:sp
+kprintf:
+  push ax
+  push bp ; state variable for stack lodsw
+  push si ; return original pointer to caller
+  mov ax, sp
+  add ax, 0x08
+  mov bp, ax
+.loop:
+  lodsb
+  cmp al,0x00
+  je .end
+  cmp al,0x25 ; '%'
+  je .fseq
+  call kputc
+  jmp .loop
+.end:
+  pop si
+  pop bp
+  mov al,0x0A
+  call kputc
+  mov al,0x0D
+  call kputc
+  pop ax
+  ret
+.fseq:
+  lodsb
+  cmp al,0x00
+  je .end
+  cmp al,0x25 ; '%'
+  je .fmt_pc
+  cmp al,0x63 ; 'c'
+  je .fmt_c
+  cmp al,0x73 ; 's'
+  je .fmt_s
+  cmp al,0x78 ; 'x'
+  je .fmt_x
+  cmp al,0x58 ; 'X'
+  je .fmt_X
+  mov al,0x3F ; '?'
+  call kputc
+  jmp .loop
+.fmt_pc:
+  mov al,0x25
+  call kputc
+  jmp .loop
+.fmt_c:
+  call kprintf_lodsw
+  call kputc
+  jmp .loop
+.fmt_s:
+  push si
+  call kprintf_lodsw
+  mov si,ax
+  call kputs
+  pop si
+  jmp .loop
+.fmt_x:
+  call kprintf_lodsw
+  call kprint8
+  jmp .loop
+.fmt_X:
+  call kprintf_lodsw
+  call kprint16
+  jmp .loop

main.asm

@@ -0,0 +1,13 @@
+cpu 8086
+
+org 0x0100
+jmp main
+
+main:
+  call mm_print
+  ret
+
+%include "kprintf.asm"
+
+; mem MUST be last because it will write after it
+%include "mem.asm"

mem.asm

@@ -0,0 +1,105 @@
+; converts a memory block type code into char representation
+; in: al
+; out: al
+; destroys ah
+mm_type:
+  push bp
+  push si
+  mov bp,.typechar
+  and ax,0x00FF
+  mov si,ax
+  mov al,[bp+si]
+  pop si
+  pop bp
+  ret
+.typechar:
+  db "F?ARU", 0
+
+mm_print:
+  push cs
+  pop ds
+  mov cx,0x0000
+  mov bp,memtab
+  mov si,0x0000
+
+.loop:
+  push si
+
+  mov ax, bp
+  add ax, si
+  add ax, 0x06
+  push ax
+
+  mov al,[bp+si+0x05]
+  push ax ; task id
+
+  mov al,[bp+si+0x04]
+  call mm_type
+  push ax ; memory type
+
+  mov bx,cx
+  add cx,[bp+si+0x00]
+  mov ax,cx
+  dec ax
+  push ax ; end addr
+  push bx ; start addr
+
+  mov si,.linefmt
+  call kprintf
+
+  pop ax
+  pop ax
+  pop ax
+  pop ax
+  pop ax
+  pop si
+
+  ; look for next line
+  mov ax,[bp+si+0x02]
+  test ax,0xFFFF
+  mov si,ax
+  jnz .loop
+  ret
+.linefmt:
+  db "%X0 %XF %c %x %s", 0
+
+; pre-filled table for memory management
+align 16
+memtab:
+  ; interrupt vector table
+  dw 0x0040
+  dw 0x0010
+  db 3
+  db 0
+  db "IVT", 0
+align 16
+  ; bios data area (writes here during runtime)
+  dw 0x0010
+  dw 0x0020
+  db 3
+  db 0
+  db "BIOS DATA", 0
+align 16
+  dw 0x9FB0
+  dw 0x0030
+  db 1
+  db 0
+  db 0
+align 16
+  dw 0x2000
+  dw 0x0040
+  db 4
+  db 0
+  db "I/O BUS", 0
+align 16
+  dw 0x3000
+  dw 0x0050
+  db 4
+  db 0
+  db "BIOS EXT", 0
+align 16
+  dw 0x1000
+  dw 0x0000
+  db 4
+  db 0
+  db "BIOS", 0