117 lines
1.9 KiB
NASM
117 lines
1.9 KiB
NASM
section .bss
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disk_buffer:
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resb 512
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disk_current:
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resb 1
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lba_supported:
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resb 1
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disk_chs: ; DL, DH, CL, CH for int 13h CHS functions
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resb 4
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disk_dap: ; disk access packet for int 13h EBIOS functions
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resb 0x10
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disk_tracks: ; heads * spt
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resw 1
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disk_spt:
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resb 1
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; Disk access packet for EBIOS extensions
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dapps: equ 0 ; byte packet size
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dapnum: equ 2 ; word number of sectors to transfer
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dapbuf: equ 4 ; dword transfer buffer
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dapsec: equ 8 ; qword absolute sector number
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dapsiz: equ 16
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section .text
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; Convert between drive number and BIOS dl
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; Bidirectional mapping
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; 0 <-> 0, 1 <-> 1, 2 <-> 0x80, 3 <-> 0x81
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dnconv: mov cx, 7
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ror dx, 1
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rol dl, 1
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dncl: rcl dl, 1
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rcr dh, 1
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loop dncl
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xchg dh, dl
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ret
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; Select a drive for I/O
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; IN dl 0=A, 1=B, 2=C, 3=D
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select: mov byte [disk_current], 0xFF
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mov byte [lba_supported], 0
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cmp dl, 0x02
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jc select_floppy
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; detect EBIOS/LBA extensions
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call dnconv
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mov byte [disk_chs], dl
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mov ah, 0x41
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mov bx, 0x55AA
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int 0x13
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test cx, 1
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jz .nolba
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cmp bx, 0xAA55
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jnz .nolba
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mov byte [lba_supported], 1
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.nolba: call seek_zero
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ret
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select_floppy:
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xor dx, dx
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xor ax, ax
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call seek
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call read
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ret
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; Set absolute sector number
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; IN dx:ax 32-bit sector number
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seek: push ax
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or ax, dx
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pop ax
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jz seek_zero
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; dx:ax = lba
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div word [disk_tracks]
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xchg ax, dx
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; dx = cylinder, ax = head * spt + sector
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div byte [disk_spt]
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; dx = cylinder, al = head, ah = sector
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xchg dl, dh
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ror dl, 1
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ror dl, 1
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or dl, ah
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;inc dx
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; dh bit 0-7: cylinder 0-7
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; dl bit 0-5: sector number 0-5
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; dl bit 6-7: cylinder 8-9
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; store
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mov byte [disk_chs+1], al
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mov word [disk_chs+2], dx
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int 3
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ret
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seek_zero:
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mov byte [disk_chs+1], 0
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mov word [disk_chs+2], 1
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ret
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; Read a sector into buffer
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read: mov ax, 0x0201
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mov dx, [disk_chs]
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mov cx, [disk_chs+2]
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lea bx, [disk_buffer]
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push cs
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pop es
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int 3
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int 0x13
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int 3
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ret
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; Write a sector into buffer
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write:
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ret
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