Meh

kernel/fcb.asm

@@ -13,7 +13,7 @@ fcb_cs:    equ 15 ; byte    cluster size: 0=128, 1=256, 2=512, ...
 fcb_co:    equ 16 ; word    start sector for theoretical cluster 0
 
 ; Read/Write pointer (6 bytes)
-fcb_left:  equ 18 ; word    number of bytes left to read from diskbuf
+fcb_left:  equ 18 ; word    number of bytes left to read in current sector
 fcb_off:   equ 20 ; dword   offset in disk (not in file)
 
 ; Link to directory item (4 bytes)
@@ -23,6 +23,7 @@ fcb_end:   equ 32
 
 fcb_open_rootdir:
   mov dl, 0x01
+  or dl, 0x80
   mov [bx], dl
   dec dl
 
@@ -30,6 +31,7 @@ fcb_open_rootdir:
   ; Default 2 heads, 9 sectors
   mov word [bx+fcb_spt], 0x0209
   xor ax, ax
+  xor dx, dx
   lea di, [bx+fcb_ss]
   ; Sector & Cluster size 128 bytes
   mov cx, (fcb_end - fcb_ss)
@@ -39,9 +41,7 @@ fcb_open_rootdir:
   call drive_read
 
   ; copy sector size
-  mov ax, [diskbuf + 0x0B]
-  ; ... save as number of valid bytes in diskbuf
-  mov WORD [bx+fcb_left], ax
+  mov ax, [diskbuf + fdc_ss]
   call log2
   sub ax, 7
   ; ... save as sector size
@@ -55,35 +55,17 @@ fcb_open_rootdir:
   mov byte [bx+fcb_cs], al
 
   ; copy sectors per track
-  mov al, [diskbuf + 0x18]
+  mov al, [diskbuf + fdc_spt]
   mov byte [bx+fcb_spt], al
 
   ; copy number of heads/sides
   mov al, [diskbuf + 0x1A]
   mov byte [bx+fcb_nos], al
 
-  ret
+  xor dx, dx
+  mov ax, [diskbuf + fdc_sf]
+  mul byte [diskbuf + fdc_fn]
+  add ax, [diskbuf + fdc_rsc]
+  int3
 
-fcb_get_sector_mask:
-  push cx
-  xor ax, ax
-  not ax
-  mov cl, [bx+fcb_ss]
-  add cl, 7
-  shl ax, cl
-  pop cx
-  ret
-
-fcb_getc:
-  push bx
-  call fcb_get_sector_mask
-  not ax
-  and ax, [bx+fcb_off]
-  xchg ax, bx
-  add bx, diskbuf
-  mov al, [bx]
-  pop bx
-  add word [bx+fcb_off], 1
-  adc word [bx+fcb_off+2], 0
-  dec word [bx+fcb_left]
   ret

kernel/main.asm

@@ -22,8 +22,7 @@ init:
   mov dx, banner
   call print_string
 
-  mov si, init_program
-  call exec
+  call exec_chain
 
   cli
 .halt:
@@ -50,6 +49,7 @@ cpm_syscall:
 %include "char.asm"
 
 %include "exec.asm"
+%include "fdc.asm"
 %include "fcb.asm"
 %include "fcbparse.asm"
 %include "drive.asm"

lib/fdc.asm

@@ -0,0 +1,14 @@
+; FDC Descriptor / BIOS parameter block
+fdc_ss:    equ 0x0B ; WORD sector size
+fdc_sc:    equ 0x0D ; BYTE sectors per cluster
+fdc_rsc:   equ 0x0E ; WORD reserved sectors
+fdc_fn:    equ 0x10 ; BYTE FAT tables
+fdc_rde:   equ 0x11 ; WORD root directory entries
+fdc_ts:    equ 0x13 ; WORD total sector count
+                    ;      0 if >65535, use lrgts then
+fdc_mi:    equ 0x15 ; BYTE media descriptor byte
+fdc_sf:    equ 0x16 ; WORD sectors per FAT
+fdc_spt:   equ 0x18 ; WORD sectors per track
+fdc_nos:   equ 0x1A ; WORD sides/heads
+fdc_po:    equ 0x1C ; DWORD partition offset
+fdc_lrgts: equ 0x20 ; DWORD large sector count