Change kernel blob format to be option rom compatible

Makefile

@@ -2,18 +2,18 @@ FD_CYLINDERS = 40
 FD_HEADS = 2
 FD_SECTORS = 9
 
-default: kernel.com
+default: kernel.rom
 
-kernel.bin: kernel/*.asm
+kernel.rom: kernel/*.asm
-	nasm -s -o $@ -I kernel kernel/main.asm
+	nasm -s -o $@ -I kernel kernel/main.asm && ./fix-rom.sh $@
 
 boot/%.bin: boot/%.asm
 	nasm -s -o $@ -I lib $<
 
-fdimage.img: boot/floppy.bin kernel.bin
+fdimage.img: boot/floppy.bin kernel.rom
 	dd if=/dev/zero bs=512 count=$$(( $(FD_CYLINDERS) * $(FD_HEADS) * $(FD_SECTORS) )) of=$@
 	mformat -i $@ -t $(FD_CYLINDERS) -h $(FD_HEADS) -n $(FD_SECTORS) -B boot/floppy.bin ::
-	mcopy -i $@ kernel.bin ::boot.bin
+	mcopy -i $@ kernel.rom ::kernel.rom
 
 clean:
-	rm -f *.com *.bin *.img boot/*.bin
+	rm -f *.com *.bin *.rom *.img boot/*.bin

boot/floppy.asm

@@ -48,10 +48,6 @@ _startup:
   ; setup stack area growing down from 0x10000
   mov ss, ax
   mov sp, ax
-  ; backup important values
-  push bx
-  push cx
-  push dx
   ; adjust CS
   jmp 0x07C0:main
 
@@ -63,6 +59,11 @@ rootdir:
   dw 0
 
 main:
+  ; backup important values
+  push bx
+  push cx
+  push dx
+
   ; setup buffer area directly at 4k
   mov ax, 0x0100
   mov ds, ax
@@ -78,13 +79,16 @@ main:
 
   ; restore important variables
   xor ax, ax
-  mov bp, ax
-  mov si, ax
-  mov di, ax
   pop dx
   pop cx
   pop bx
-  jmp 0x0100:0000
+  mov di, [0x001A]
+  mov ax, [di+0x1A]
+  push ds
+  push ax
+  retf
+  call error
+  db "ROM ERROR", 0
 
 ; Write AX, a string and bail out
 ; Return pointer is the string start
@@ -228,9 +232,9 @@ loadblk:
 times (0x1F0 - ($-$$)) db 0
 
 bootfilename:
-  db "BOOT"
+  db "KERNEL"
   times (0x1F8 - ($-$$)) db " "
-  db "BIN"
+  db "ROM"
 
 times (0x1FE - ($-$$)) db 0
 

fix-rom.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+setbyte() {
+  printf "\x$3"|dd status=none seek="$2" bs=1 count=1 conv=notrunc of="$1"
+}
+
+[ -n "$1" ] || exit 1
+
+setbyte "$1" 2 $(stat -c "%s" "$1"|awk '{printf("%02x",$1/512)}')
+
+setbyte "$1" 41 00
+checksum=$(xxd -p -c 1 "$1"|sed 's/^/0x/'|awk '{s+=$1} END {printf("%02x\n",256-s%256)}')
+setbyte "$1" 41 "$checksum"

kernel/main.asm

@@ -1,36 +1,119 @@
-; assumptions about the starting envionment
+cpu 8086
-cpu 8086
+org 0x0000
-org 0x0000
+  db 0x55, 0xAA, 0x00
-
+  jmp optrom_init
-_startup:
+
-  mov ax, cs
+times (0x1A - ($-$$)) db 0
-  mov ss, ax
+  dw pnp
-  mov sp, 0x0000
+
-  ; <0x0010 is BIOS segment when relocated to HMA
+align 16
-  ; so we need a nop sled
+pnp:
-  times (0x10 - ($-$$)) nop
+  db "$PnP"
-main:
+  db 1 ; version 1
-  call intr_init
+  db 2 ; 2 * 16 length
-
+  dw 0 ; offset of next header
-  int 3
+  db 0
-
+  db 0 ; checksum (filled by fix-rom)
-  mov ah, 0x01
+  dd 0 ; device identifier
-  int 0x21
+  dw .vendor ; manufacturer string
-  mov dl, al
+  dw .product ; product name string
-  mov ah, 0x02
+  db 0,0,0 ; device type string
-  int 0x21
+  db 0x20 ; device indicator, bit for "read cacheable" set
-
+  dw 0 ; boot connection vector
-  sti
+  dw 0 ; boot disconnect vector
-.halt:
+  dw start ; bootstrap entry point
-  hlt
+  dw 0 ; reserved
-  jmp .halt
+  dw 0
-
+.vendor:
-%include "intr.asm"
+  db "Nero", 0
-%include "debug.asm"
+.product:
-%include "kprintf.asm"
+  db "2B", 0
-%include "dosapi.asm"
+
-
+align 16
-_reloc_end:
+optrom_init:
-
+  push di
-align 16
+  push es
-heap:
+  xor ax, ax
+  mov es, ax
+  mov di, 0x0060 ; vector (0x18 * 4 bytes)
+  mov ax, start
+  stosw
+  mov ax, cs
+  stosw
+  pop es
+  pop di
+  retf
+
+start:
+  call intr_init
+
+  sti
+
+  mov si, 0x0000
+  mov ds, si
+
+.loop:
+  push bx
+  mov dx, 0x0000
+  mov ah, 0x02
+  mov bx, 0x0000
+  int 0x10
+  pop bx
+
+  call dump
+
+  mov ah, 0x01
+  int 0x21
+
+  cmp al, 0x30
+  jne .notup
+  sub bx, 0x0100
+.notup:
+  cmp al, 0x31
+  jne .notdown
+  add bx, 0x0100
+.notdown:
+  jmp .loop
+
+.halt:
+  hlt
+  jmp .halt
+
+dump:
+  mov si, bx
+  mov cx, 0x10
+.nextline:
+  mov ax, si
+  call kprint16
+
+  mov al, 0x3A
+  call kputc
+  mov al, 0x20
+  call kputc
+
+  push cx
+  mov cx, 0x0020
+.bytes:
+  lodsb
+  call kprint8
+  loop .bytes
+  pop cx
+
+  mov al,0x20
+  call kputc
+  mov al,0x0A
+  call kputc
+  mov al,0x0D
+  call kputc
+
+  loop .nextline
+  ret
+
+%include "intr.asm"
+%include "debug.asm"
+%include "kprintf.asm"
+%include "dosapi.asm"
+
+_reloc_end:
+
+align 512