169 lines
2.5 KiB
NASM
169 lines
2.5 KiB
NASM
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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