Another attempt at implementing a block layer
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6f7fc05171
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e86b1ba004
168
kernel/disk.asm
Normal file
168
kernel/disk.asm
Normal file
@ -0,0 +1,168 @@
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disk_num: equ 0x40 ; BYTE drive number (A=0)
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disk_heads: equ 0x41 ; BYTE number of heads/sides
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disk_parm: equ 0x42 ; 11 BYTES for int 0x1E
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disk_spt: equ 0x46 ; - BYTE
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disk_parm_init:
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push ax
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push si
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push di
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push ds
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; invalidate existing data
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mov byte [disk_num], 0xFF
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xor ax, ax
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mov ds, ax
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; if int 0x1E is already pointing to us,
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; we have nothing to copy
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mov di, disk_parm
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lds si, [0x1E*4]
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cmp si, di
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je .correctparm
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; copy bios table into our location
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mov cx, 11
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rep movsb
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; make the interrupt vector point to our address
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xor ax, ax
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mov ds, ax
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mov [0x1E*4], di
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mov ax, cs
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mov [0x1E*4+2], ax
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.correctparm:
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pop ds
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pop di
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pop si
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pop ax
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ret
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disk_load_bpb:
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mov ax, 0x0201
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mov cx, 0x0001
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xor dh, dh
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mov bx, diskbuf
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stc
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int 0x13
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jnc .end
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; try a second time
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mov ax, 0x0201
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int 0x13
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jnc .end
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; try a third time
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mov ax, 0x0201
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int 0x13
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.end:
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ret
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disk_select:
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push ax
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push cx
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push dx
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push bx
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cmp byte [disk_num], dl
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je .end
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mov byte [disk_num], dl
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call disk_load_bpb
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jc .end
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; Validate and apply sector size
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mov ax, [diskbuf+fdc_ss]
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; test ax, 0xF87F
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; jnz .nobpd
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call log2
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sub al, 7
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mov [disk_parm+3], al
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; fetch sectors per track
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mov al, [diskbuf+fdc_spt]
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mov [disk_parm+4], al
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; fetch number of sides/heads
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mov ax, [diskbuf+fdc_nos]
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mov [disk_heads], al
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xor ah, ah
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int 0x13
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.end:
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pop bx
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pop dx
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pop cx
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pop ax
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ret
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; Setup CX, DX and BX for int 13h transfer
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; IN BX ptr to 32-bit number
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; OUT CL Sector number
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; CH Cylinder number
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; DL Drive number
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; DH Head number
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; BX Sector buffer
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disk_prepare_chs:
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mov ax, word [bx]
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mov dx, word [bx+2]
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xor bh, bh
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mov bl, byte [disk_spt]
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div word bx ; ax:temp = (lba / spt)
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inc dx ; dx:sector = (lba % spt) + 1
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mov cl, dl ; sector number
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xor bx, bx
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mov bl, byte [disk_heads]
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xor dx, dx
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div word bx ; ax:cylinder = (temp / nos)
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; dx:head = (temp % nos)
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mov ch, al ; cylinder number
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mov dh, dl ; head number
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mov dl, byte [disk_num]
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mov bx, diskbuf
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ret
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; Read a sector into diskbuf
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; IN BX ptr to DWORD giving sector number
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disk_read:
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push ax
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push cx
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push dx
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push bx
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call disk_prepare_chs
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mov ax, 0x0201
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int 0x13
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pop bx
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pop dx
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pop cx
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pop ax
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ret
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; Write a sector from diskbuf
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; IN BX ptr to DWORD giving sector number
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disk_write:
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push ax
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push cx
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push dx
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push bx
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call disk_prepare_chs
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mov ax, 0x0301
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int 0x13
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pop bx
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pop dx
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pop cx
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pop ax
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ret
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@ -1,70 +0,0 @@
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; Load a sector from drive.
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; IN DX:AX sector number (lba)
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; BX ptr to FCB
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; OUT CL Sector number
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; CH Cylinder number
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; DH Head number
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drive_chs_calc:
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push bx ; backup fcb ptr
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mov bx, [bx+fcb_spt] ; nos is in BH now
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push bx ; backup nos
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xor bh, bh ; zero out nos so spt is left
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div word bx ; ax:temp = (lba / spt)
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inc dx ; dx:sector = (lba % spt) + 1
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mov cl, dl ; sector number
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pop bx ; restore nos
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xchg bl, bh ; put nos into bl
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xor bh, bh ; zero out spt
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div word bx ; ax:cylinder = (temp / nos)
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; dx:head = (temp % nos)
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mov ch, al ; cylinder number
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mov dh, dl ; head number
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pop bx ; restore fcb ptr
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ret
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; Load a sector from drive.
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; IN DX:AX sector number
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; BX ptr to FCB
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drive_read:
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push ax
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push cx
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push dx
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push bx
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push si
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mov cx, dx
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or cx, ax
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jz .fast
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call drive_chs_calc
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mov si, 5 ; retry count
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.try:
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mov dl, [bx+fcb_drv] ; drive number
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and dl, 0x7F
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dec dl
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mov ax, 0x0201
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mov bx, diskbuf
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; try read
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int 0x13
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jnc .end
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; reset disk
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mov ah, 0x00
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int 0x13
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; loop with si
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dec si
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test si, si
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jnz .try
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stc
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.end:
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pop si
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pop bx
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pop dx
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pop cx
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pop ax
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ret
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.fast: ; fast lane for boot sector
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inc cl
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jmp .try
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@ -7,7 +7,6 @@ exec:
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mov bx, sp
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call fcb_parse
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call fcb_open_rootdir
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add sp, 0x20
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pop bx
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@ -5,67 +5,4 @@ fcb_drv: equ 0 ; 1 byte, 1=A: 2=B: 3=C:
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fcb_fn: equ 1 ; 8 bytes
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fcb_ext: equ 9 ; 3 bytes
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; Drive & FS data (6 bytes)
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fcb_spt: equ 12 ; byte sectors per track
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fcb_nos: equ 13 ; byte number of sides/heads
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fcb_ss: equ 14 ; byte sector size: 0=128, 1=256, 2=512, ...
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fcb_cs: equ 15 ; byte cluster size: 0=128, 1=256, 2=512, ...
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fcb_co: equ 16 ; word start sector for theoretical cluster 0
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; Read/Write pointer (6 bytes)
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fcb_left: equ 18 ; word number of bytes left to read in current sector
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fcb_off: equ 20 ; dword offset in disk (not in file)
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; Link to directory item (4 bytes)
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fcb_ds: equ 24 ; dword offset of directory item
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fcb_end: equ 32
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fcb_open_rootdir:
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mov dl, 0x01
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or dl, 0x80
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mov [bx], dl
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dec dl
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; Setup default data
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; Default 2 heads, 9 sectors
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mov word [bx+fcb_spt], 0x0209
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xor ax, ax
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xor dx, dx
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lea di, [bx+fcb_ss]
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; Sector & Cluster size 128 bytes
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mov cx, (fcb_end - fcb_ss)
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rep stosb
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; load first sector
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call drive_read
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; copy sector size
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mov ax, [diskbuf + fdc_ss]
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call log2
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sub ax, 7
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; ... save as sector size
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mov byte [bx+fcb_ss], al
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; copy cluster size
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xor ah, ah
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mov al, [diskbuf + 0x0D]
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call log2
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add al, [bx+fcb_ss]
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mov byte [bx+fcb_cs], al
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; copy sectors per track
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mov al, [diskbuf + fdc_spt]
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mov byte [bx+fcb_spt], al
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; copy number of heads/sides
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mov al, [diskbuf + 0x1A]
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mov byte [bx+fcb_nos], al
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xor dx, dx
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mov ax, [diskbuf + fdc_sf]
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mul byte [diskbuf + fdc_fn]
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add ax, [diskbuf + fdc_rsc]
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int3
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ret
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fcb_type: equ 12 ; BYTE type identifier
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@ -22,7 +22,10 @@ init:
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mov dx, banner
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call print_string
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call exec_chain
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call disk_parm_init
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mov dl, 0x00
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call disk_select
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cli
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.halt:
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@ -52,6 +55,6 @@ cpm_syscall:
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%include "fdc.asm"
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%include "fcb.asm"
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%include "fcbparse.asm"
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%include "drive.asm"
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%include "disk.asm"
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%include "log2.asm"
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%include "dump.asm"
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