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- ; load 'dh' sectors from drive 'dl' into ES:BX
- disk_load:
- pusha
- ; reading from disk requires setting specific values in all registers
- ; so we will overwrite our input parameters from 'dx'. Let's save it
- ; to the stack for later use.
- push dx
- mov ah, 0x02 ; ah <- int 0x13 function. 0x02 = 'read'
- mov al, dh ; al <- number of sectors to read (0x01 .. 0x80)
- mov cl, 0x02 ; cl <- sector (0x01 .. 0x11)
- ; 0x01 is our boot sector, 0x02 is the first 'available' sector
- mov ch, 0x00 ; ch <- cylinder (0x0 .. 0x3FF, upper 2 bits in 'cl')
- ; dl <- drive number. Our caller sets it as a parameter and gets it from BIOS
- ; (0 = floppy, 1 = floppy2, 0x80 = hdd, 0x81 = hdd2)
- mov dh, 0x00 ; dh <- head number (0x0 .. 0xF)
- ; [es:bx] <- pointer to buffer where the data will be stored
- ; caller sets it up for us, and it is actually the standard location for int 13h
- int 0x13 ; BIOS interrupt
- jc disk_error ; if error (stored in the carry bit)
- pop dx
- cmp al, dh ; BIOS also sets 'al' to the # of sectors read. Compare it.
- jne sectors_error
- popa
- ret
- disk_error:
- mov bx, DISK_ERROR
- call print
- call print_nl
- mov dh, ah ; ah = error code, dl = disk drive that dropped the error
- call print_hex ; check out the code at http://stanislavs.org/helppc/int_13-1.html
- jmp disk_loop
- sectors_error:
- mov bx, SECTORS_ERROR
- call print
- disk_loop:
- jmp $
- DISK_ERROR: db "Disk read error", 0
- SECTORS_ERROR: db "Incorrect number of sectors read", 0
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