Implement ramdisk i/o, advance kernel printf

Makefile

@@ -20,7 +20,7 @@ endif
 default: kernel.rom
 
 kernel.rom: kernel/*.asm
-	nasm -s -o $@ -I kernel kernel/main.asm && scripts/fix-rom.sh $@
+	nasm -s -o $@ -I lib -I kernel kernel/main.asm && scripts/fix-rom.sh $@
 
 boot/%.bin: boot/%.asm
 	nasm -s -o $@ -I lib $<

kernel/dosapi.asm

@@ -15,5 +15,5 @@ isr_getc_echo:
 
 isr_putc:
   mov al, dl
-  call kputc
+  call putc
   iret

kernel/main.asm

@@ -1,8 +1,17 @@
 cpu 8086
 org 0x0000
-  db 0x55, 0xAA, 0x00
+  db 0x55, 0xAA
+optrom_length:
+  db 0x00
   jmp optrom_init
 
+str_vendor:
+  db "Nero", 0
+
+align 16
+str_product:
+  db "Nero DOS", 0
+
 times (0x1A - ($-$$)) db 0
   dw pnp
 
@@ -15,8 +24,8 @@ pnp:
   db 0
   db 0 ; checksum (filled by fix-rom)
   dd 0 ; device identifier
-  dw .vendor ; manufacturer string
-  dw .product ; product name string
+  dw str_vendor ; manufacturer string
+  dw str_product ; product name string
   db 0,0,0 ; device type string
   db 0x20 ; device indicator, bit for "read cacheable" set
   dw 0 ; boot connection vector
@@ -24,15 +33,9 @@ pnp:
   dw start ; bootstrap entry point
   dw 0 ; reserved
   dw 0
-.vendor:
-  db "Nero", 0
-.product:
-  db "2B", 0
 
 align 16
 optrom_init:
-  push di
-  push es
   xor ax, ax
   mov es, ax
   mov di, 0x0060 ; vector (0x18 * 4 bytes)
@@ -40,74 +43,71 @@ optrom_init:
   stosw
   mov ax, cs
   stosw
-  pop es
-  pop di
   retf
 
-start:
-  call intr_init
-
-  sti
-
-  mov si, 0x0000
-  mov ds, si
-
-.loop:
+putc:
   push bx
-  mov dx, 0x0000
-  mov ah, 0x02
+  push cx
+  mov ah, 0x0e
   mov bx, 0x0000
   int 0x10
+  pop cx
   pop bx
+  ret
 
-  call dump
+announce:
+  push cs
+  mov ax, str_product
+  push ax
+  call printf
+  db "%S (CS=%Xh)", 0x0A, 0x0D, 0x00
+  add sp, 4
+  ret
 
-  mov ah, 0x01
-  int 0x21
+start:
+  mov ax, cs
+  mov ds, ax
 
-  cmp al, 0x30
-  jne .notup
-  sub bx, 0x0100
-.notup:
-  cmp al, 0x31
-  jne .notdown
-  add bx, 0x0100
-.notdown:
-  jmp .loop
+  call announce
+
+  ; clear memory until 0x01000
+  xor ax, ax
+  mov es, ax
+  mov di, 0x500
+  mov cx, 0xB00
+  rep stosb
+
+  call intr_init
+  sti
+
+  sub sp, 0x10
+  mov si, sp
+  mov word [ss:si+0x00], 0
+  mov word [ss:si+0x02], 1
+  mov word [ss:si+0x04], 0
+  mov word [ss:si+0x06], 0x2000
+  mov word [ss:si+0x08], 0x07fc
+  mov word [ss:si+0x0A], 0
+  mov word [ss:si+0x0C], 0
+  mov word [ss:si+0x0E], 0
+  mov ah, 0x42
+
+  push ss
+  pop ds
+  call ramdisk_io
+  push ax
+  call printf
+  db "AX=%X", 0x0A, 0x0D, 0x00
+  pop ax
+
+  add sp, 0x10
 
 .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 "ramdisk.inc"
+%include "printf.inc"
 
 %include "intr.asm"
 %include "debug.asm"

kernel/ramdisk.inc

@@ -0,0 +1,86 @@
+; Spanning whole conventional memory
+; Sector size 0x200 (512 bytes)
+; Start address 0x00600, 3 hidden sectors for IVT and BDA
+; Kernel .data may be in reserved sectors
+
+; Ramdisk I/O, similar invocation to BIOS int 13h
+; in	AH	42=read, 43=write
+; in    DS:SI   location of disk address packet
+; out	AH	error code or 00 (also in CF)
+ramdisk_io:
+  ; backup original values
+  push cx
+  push dx
+  push si
+  push di
+  push ds
+  push es
+
+  ; 3 most significant addr bytes must be all zero
+  test WORD [ds:si+0x0E], 0xFFFF
+  jnz .invaddr
+  test WORD [ds:si+0x0C], 0xFFFF
+  jnz .invaddr
+  test WORD [ds:si+0x0A], 0xFFFF
+  jnz .invaddr
+
+  ; calculate segment register for ramdisk access
+  mov dx, [ds:si+0x08]
+  cmp dx, 0x07fd ; 0x800 sectors in adress space, 3 hidden
+  jge .invaddr
+  mov cl, 0x05 ; 2^5 = 32 paragraphs per sector
+  sal dx, cl
+  add dx, 0x0060 ; 3 hidden sectors
+  xor cx, cx
+  push cx ; offset = 0
+  push dx ; segment
+
+  ; store addresses for buffer access
+  mov dx, [ds:si+0x04]
+  push dx ; offset
+  mov dx, [ds:si+0x06]
+  push dx ; segment
+
+  ; setup transfer length (in words) in CX
+  mov dx, [ds:si+0x02] ; sector count
+  mov cx, 0x0008 ; 2^8 = 256 words per sector
+  sal dx, cl
+  xchg dx, cx
+
+  cmp ah, 0x42
+  je .read
+  cmp ah, 0x43
+  je .write
+  sub sp, 8 ; remove src & dst pointers from stack
+.invval:
+  mov ah, 0x01
+  stc
+  jmp .ret
+.invaddr: ; out of bounds
+  mov ah, 0x04
+  stc
+  jmp .ret
+.read:
+  pop es ; ES:DI buffer
+  pop di
+  pop ds ; DS:SI ramdisk data
+  pop si
+  rep movsw
+  clc
+  jmp .ret
+.write:
+  pop ds ; DS:SI buffer
+  pop si
+  pop es ; ES:DI ramdisk data
+  pop di
+  rep movsw
+  clc
+.ret:
+  ; restore backupped values
+  pop es
+  pop ds
+  pop di
+  pop si
+  pop dx
+  pop cx
+  ret

lib/printf.inc

@@ -0,0 +1,80 @@
+printf:
+  cld
+  pop si
+  push bp
+  mov bp, sp
+.loop:
+  mov al, [cs:si]
+  inc si
+  cmp al, 0x00
+  je .end
+  cmp al, 0x25
+  je .handle_25h
+.literal:
+  call putc
+  jmp .loop
+.end:
+  pop bp
+  push si
+  ret
+.handle_25h:
+  mov al, [cs:si]
+  inc si
+  cmp al, 0x25
+  je .literal
+  cmp al, 0x58 ; 'X'
+  je .printhex
+  cmp al, 0x55 ; 'U'
+  je .printdec
+  cmp al, 0x53 ; 'S'
+  je .printstr
+  mov al, 0x3F
+  jmp .literal
+.printhex:
+  add bp, 2
+  mov ax, [bp]
+  mov bx, 0x0010
+  call print_number
+  jmp .loop
+.printdec:
+  add bp, 2
+  mov ax, [bp]
+  mov bx, 0x000A
+  call print_number
+  jmp .loop
+.printstr:
+  add bp, 2
+  mov ax, [bp]
+  call print_string
+  jmp .loop
+
+print_number:
+  xor dx, dx
+  div bx ; ax = dx:ax / 10, dx = dx:ax % 10
+  and ax, ax
+  jz .print
+  push dx
+  call print_number
+  pop dx
+.print:
+  mov al, dl
+  add al, 0x30
+  cmp al, 0x3A
+  jl .noadj
+  add al, 0x07
+.noadj:
+  call putc
+  ret
+
+print_string:
+  push si
+  mov si, ax
+.loop:
+  lodsb
+  cmp al, 0x00
+  je .end
+  call putc
+  jmp .loop
+.end:
+  pop si
+  ret