Another attempt at implementing a block layer

kernel/disk.asm

@@ -0,0 +1,168 @@
+disk_num:   equ 0x40 ; BYTE drive number (A=0)
+disk_heads: equ 0x41 ; BYTE number of heads/sides
+disk_parm:  equ 0x42 ; 11 BYTES for int 0x1E
+disk_spt:   equ 0x46 ;  - BYTE
+
+disk_parm_init:
+  push ax
+  push si
+  push di
+  push ds
+
+  ; invalidate existing data
+  mov byte [disk_num], 0xFF
+
+  xor ax, ax
+  mov ds, ax
+
+  ; if int 0x1E is already pointing to us,
+  ; we have nothing to copy
+  mov di, disk_parm
+  lds si, [0x1E*4]
+  cmp si, di
+  je .correctparm
+
+  ; copy bios table into our location
+  mov cx, 11
+  rep movsb
+
+  ; make the interrupt vector point to our address
+  xor ax, ax
+  mov ds, ax
+  mov [0x1E*4], di
+  mov ax, cs
+  mov [0x1E*4+2], ax
+
+.correctparm:
+  pop ds
+  pop di
+  pop si
+  pop ax
+  ret
+
+disk_load_bpb:
+  mov ax, 0x0201
+  mov cx, 0x0001
+  xor dh, dh
+  mov bx, diskbuf
+  stc
+
+  int 0x13
+  jnc .end
+
+  ; try a second time
+  mov ax, 0x0201
+  int 0x13
+  jnc .end
+
+  ; try a third time
+  mov ax, 0x0201
+  int 0x13
+.end:
+  ret
+
+disk_select:
+  push ax
+  push cx
+  push dx
+  push bx
+
+  cmp byte [disk_num], dl
+  je .end
+  mov byte [disk_num], dl
+  call disk_load_bpb
+  jc .end
+
+  ; Validate and apply sector size
+  mov ax, [diskbuf+fdc_ss]
+; test ax, 0xF87F
+; jnz .nobpd
+  call log2
+  sub al, 7
+  mov [disk_parm+3], al
+
+  ; fetch sectors per track
+  mov al, [diskbuf+fdc_spt]
+  mov [disk_parm+4], al
+
+  ; fetch number of sides/heads
+  mov ax, [diskbuf+fdc_nos]
+  mov [disk_heads], al
+
+  xor ah, ah
+  int 0x13
+.end:
+  pop bx
+  pop dx
+  pop cx
+  pop ax
+  ret
+
+; Setup CX, DX and BX for int 13h transfer
+; IN   BX  ptr to 32-bit number
+; OUT  CL  Sector number
+;      CH  Cylinder number
+;      DL  Drive number
+;      DH  Head number
+;      BX  Sector buffer
+disk_prepare_chs:
+  mov ax, word [bx]
+  mov dx, word [bx+2]
+
+  xor bh, bh
+  mov bl, byte [disk_spt]
+
+  div word bx  ; ax:temp     = (lba / spt)
+  inc dx       ; dx:sector   = (lba % spt) + 1
+  mov cl, dl   ; sector number
+
+  xor bx, bx
+  mov bl, byte [disk_heads]
+
+  xor dx, dx
+  div word bx  ; ax:cylinder = (temp / nos)
+               ; dx:head     = (temp % nos)
+  mov ch, al   ; cylinder number
+  mov dh, dl   ; head number
+
+  mov dl, byte [disk_num]
+  mov bx, diskbuf
+  ret
+
+; Read a sector into diskbuf
+; IN BX ptr to DWORD giving sector number
+disk_read:
+  push ax
+  push cx
+  push dx
+  push bx
+
+  call disk_prepare_chs
+
+  mov ax, 0x0201
+  int 0x13
+
+  pop bx
+  pop dx
+  pop cx
+  pop ax
+  ret
+
+; Write a sector from diskbuf
+; IN BX ptr to DWORD giving sector number
+disk_write:
+  push ax
+  push cx
+  push dx
+  push bx
+
+  call disk_prepare_chs
+
+  mov ax, 0x0301
+  int 0x13
+
+  pop bx
+  pop dx
+  pop cx
+  pop ax
+  ret

kernel/drive.asm

@@ -1,70 +0,0 @@
-; Load a sector from drive.
-; IN    DX:AX   sector number (lba)
-;       BX      ptr to FCB
-; OUT	CL	Sector number
-;	CH	Cylinder number
-;	DH	Head number
-drive_chs_calc:
-  push bx      ; backup fcb ptr
-  mov bx, [bx+fcb_spt] ; nos is in BH now
-  push bx      ; backup nos
-  xor bh, bh   ; zero out nos so spt is left
-  div word bx  ; ax:temp     = (lba / spt)
-  inc dx       ; dx:sector   = (lba % spt) + 1
-  mov cl, dl   ; sector number
-
-  pop bx       ; restore nos
-  xchg bl, bh  ; put nos into bl
-  xor bh, bh   ; zero out spt
-  div word bx  ; ax:cylinder = (temp / nos)
-               ; dx:head     = (temp % nos)
-  mov ch, al   ; cylinder number
-  mov dh, dl   ; head number
-
-  pop bx       ; restore fcb ptr
-  ret
-
-; Load a sector from drive.
-; IN    DX:AX   sector number
-;	BX	ptr to FCB
-drive_read:
-  push ax
-  push cx
-  push dx
-  push bx
-  push si
-
-  mov cx, dx
-  or cx, ax
-  jz .fast
-
-  call drive_chs_calc
-
-  mov si, 5        ; retry count
-.try:
-  mov dl, [bx+fcb_drv] ; drive number
-  and dl, 0x7F
-  dec dl
-  mov ax, 0x0201
-  mov bx, diskbuf
-  ; try read
-  int 0x13
-  jnc .end
-  ; reset disk
-  mov ah, 0x00
-  int 0x13
-  ; loop with si
-  dec si
-  test si, si
-  jnz .try
-  stc
-.end:
-  pop si
-  pop bx
-  pop dx
-  pop cx
-  pop ax
-  ret
-.fast: ; fast lane for boot sector
-  inc cl
-  jmp .try

kernel/exec.asm

@@ -7,7 +7,6 @@ exec:
   mov bx, sp
 
   call fcb_parse
-  call fcb_open_rootdir
 
   add sp, 0x20
   pop bx

kernel/fcb.asm

@@ -5,67 +5,4 @@ fcb_drv:   equ 0  ; 1 byte, 1=A: 2=B: 3=C:
 fcb_fn:    equ 1  ; 8 bytes
 fcb_ext:   equ 9  ; 3 bytes
 
-; Drive & FS data (6 bytes)
+fcb_type:  equ 12 ; BYTE type identifier
-fcb_spt:   equ 12 ; byte    sectors per track
-fcb_nos:   equ 13 ; byte    number of sides/heads
-fcb_ss:    equ 14 ; byte    sector size: 0=128, 1=256, 2=512, ...
-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 in current sector
-fcb_off:   equ 20 ; dword   offset in disk (not in file)
-
-; Link to directory item (4 bytes)
-fcb_ds:    equ 24 ; dword   offset of directory item
-
-fcb_end:   equ 32
-
-fcb_open_rootdir:
-  mov dl, 0x01
-  or dl, 0x80
-  mov [bx], dl
-  dec dl
-
-  ; Setup default data
-  ; 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)
-  rep stosb
-
-  ; load first sector
-  call drive_read
-
-  ; copy sector size
-  mov ax, [diskbuf + fdc_ss]
-  call log2
-  sub ax, 7
-  ; ... save as sector size
-  mov byte [bx+fcb_ss], al
-
-  ; copy cluster size
-  xor ah, ah
-  mov al, [diskbuf + 0x0D]
-  call log2
-  add al, [bx+fcb_ss]
-  mov byte [bx+fcb_cs], al
-
-  ; copy sectors per track
-  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
-
-  xor dx, dx
-  mov ax, [diskbuf + fdc_sf]
-  mul byte [diskbuf + fdc_fn]
-  add ax, [diskbuf + fdc_rsc]
-  int3
-
-  ret

kernel/main.asm

@@ -22,7 +22,10 @@ init:
   mov dx, banner
   call print_string
 
-  call exec_chain
+  call disk_parm_init
+
+  mov dl, 0x00
+  call disk_select
 
   cli
 .halt:
@@ -52,6 +55,6 @@ cpm_syscall:
 %include "fdc.asm"
 %include "fcb.asm"
 %include "fcbparse.asm"
-%include "drive.asm"
+%include "disk.asm"
 %include "log2.asm"
 %include "dump.asm"