83 lines
1.2 KiB
NASM
83 lines
1.2 KiB
NASM
; *****************************
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; Reads bytes from disk
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; *****************************
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; IN:
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; EAX = Start address to load low 32
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; EBP = Start address to load high 32
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; DL = Drive number
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; ES = Buffer segment
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; BX = Buffer offset
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; ECX = Byte count
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; OUT:
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; Carry if error
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read_sectors:
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pusha
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mov si, .da_struct
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mov word [si], 16
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mov word [si+2], 1
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mov word [si+4], bx
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mov word [si+6], es
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push dx
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push si
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push eax
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push ebp
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; Get bytes per sector
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mov ah, 0x48
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mov si, .drive_params
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mov word [si], 30 ; buf_size
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int 0x13
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jc .done
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mov bp, word [si+24] ; bytes_per_sect
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; ECX byte count to CX sector count
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mov ax, cx
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shr ecx, 16
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mov dx, cx
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xor cx, cx
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div bp
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test dx, dx
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setnz cl
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add cx, ax
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pop edx
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pop eax
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pop si
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; EBP:EAX address to EAX LBA sector
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div ebp
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mov dword [si+8], eax
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mov dword [si+12], 0
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pop dx
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.loop:
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mov ah, 0x42
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clc
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int 0x13
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jc .done
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add word [si+4], bp
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xor ebx, ebx
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inc dword [si+8]
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seto bl
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add dword [si+12], ebx
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loop .loop
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.done:
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popa
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ret
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.da_struct: equ 0x8000
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.drive_params: equ 0x8010
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