49 lines
1.2 KiB
ArmAsm
49 lines
1.2 KiB
ArmAsm
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; Utilities to read data from the disk. Used to load the kernel
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; into main memory
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load_disk:
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; Loads 'dh' sectors from drive 'dl' (this
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; register is set by the BIOS before calling
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; the bootloader) into es:bx
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pusha
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push dx
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mov ah, 0x2 ; Perform a read operation
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mov al, dh ; Number of sectors
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mov cl, 0x2 ; 0x1 is us, so 0x2 is the first sector we want
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mov ch, 0x0 ; Cylinder 0
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mov dh, 0x0 ; Head position is 0 too
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int 0x13 ; Once this returns, the data will be in es:bx
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jc disk_error ; If an error occurs, the carry bit is set
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pop dx
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; The BIOS tells us how many sectors have been
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; actually read. If the desired and actual value
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; don't match, an error occurred
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cmp al, dh
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jne sectors_error
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popa
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ret
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disk_error:
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mov si, disk_read_error_msg
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call bios_print
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mov dh, ah ; Error code is in ah
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call bios_printh
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call bios_newline
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jmp disk_loop
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sectors_error:
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mov si, disk_sectors_error_msg
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call bios_println
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disk_loop:
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jmp $
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disk_read_info: db "Booting from disk type ", 0
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disk_read_error_msg: db "Read error: ", 0
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disk_sectors_error_msg: db "Read error (wrong number of sectors)", 0
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