Implement FCB parsing in kernel

kernel/exec.asm

@@ -0,0 +1,14 @@
+; Exec the cmdline at SI or 0x81
+exec_chain:
+  mov si, 0x81
+exec:
+  push bx
+  sub sp, 36
+  mov bx, sp
+
+  call fcb_parse
+  call fcb_print
+
+  add sp, 36
+  pop bx
+  ret

kernel/fcb.asm

@@ -0,0 +1,68 @@
+; Parse ASCIIZ string into FCB
+; IN	SI	ptr to filename
+;       BX	ptr to FCB
+fcb_parse:
+  push si
+  push di
+  push ax
+  mov di, bx
+  inc di
+.cleanout:
+  push di
+  mov cx, 0x0A
+  mov al, 0x20
+  rep stosb
+  pop di
+.base_loop:
+  call .read
+  cmp al, 0x2E
+  je .ext_start
+  cmp al, 0x20
+  je .ret
+  stosb
+  jmp .base_loop
+.ext_start:
+  mov di, bx
+  add di, 9
+.ext_loop:
+  call .read
+  cmp al, 0x20
+  je .ret
+  stosb
+  jmp .ext_loop
+.read:
+  lodsb
+  test al, al
+  jz .eret
+  cmp al, 0x0D
+  je .eret
+  ret
+.eret:
+  pop ax
+.ret:
+  pop ax
+  pop di
+  pop si
+  ret
+
+; Print a FCB (for debugging)
+; IN	BX	ptr FCB
+fcb_print:
+  push dx
+  push cx
+  push si
+  mov si, bx
+  inc si
+  mov cx, 11
+.loop:
+  lodsb
+  mov dl, al
+  call putc
+  loop .loop
+  mov dl, 0x26
+  call putc
+.ret:
+  pop si
+  pop cx
+  pop dx
+  ret

kernel/main.asm

@@ -2,8 +2,18 @@ cpu 8086
 
 ; Memory layout (starting from top)
 %define self    0xF000
+
+; A single sector for disk i/o
 %define diskbuf (self-0x200)
-%define stack   (diskbuf) ; end addr, grows down
+
+; BYTE sectors/track and BYTE number of sides
+; 4 times for A: B: C: and D:
+%define chstab  (diskbuf - (4*2))
+
+; DWORD partition offset for C: and D:
+%define parttab (chstab - (2*4))
+
+%define stack   (parttab)
 
 org self
 jmp init
@@ -28,13 +38,18 @@ init:
   mov sp, stack
 
   call print_banner
-  int3
+
+  mov si, init_program
+  call exec
 
   cli
 .halt:
   hlt
   jmp .halt
 
+init_program:
+  db "HELLO.COM", 0
+
 cpm_syscall:
   cmp cl, 0x02
   je putc
@@ -52,6 +67,5 @@ putc:
   pop ax
   ret
 
-%include "string.asm"
-
-kernel_end:
+%include "exec.asm"
+%include "fcb.asm"