Subversion Repositories eco32

;

; mbr.s -- the master boot record

;

; $8  I/O base address

; $9  temporary value

; $10 character

; $11 pointer to string

; $29 stack pointer

; $31 return address

        .set    tba,0xF0300000  ; terminal base address

start:

        sub     $29,$29,4       ; save return register

        stw     $31,$29,0

        add     $8,$0,tba        ; set I/O base address

        add     $11,$0,msg       ; pointer to string

loop:

        ldbu    $10,$11,0        ; get char

        beq     $10,$0,stop      ; null - finished

        jal     out             ; output char

        add     $11,$11,1       ; bump pointer

        j       loop            ; next char

stop:

        ldw     $31,$29,0        ; restore return register

        add     $29,$29,4

        jr      $31             ; return

out:

        ldw     $9,$8,8         ; get status

        and     $9,$9,1         ; xmtr ready?

        beq     $9,$0,out        ; no - wait

        stw     $10,$8,12       ; send char

        jr      $31             ; return

msg:

        .byte   0x0D, 0x0A

        .byte   "Error: This is the default MBR, "

        .byte   "which cannot load anything."

        .byte   0x0D, 0x0A

        .byte   "Please replace the disk, or "

        .byte   "write an operating system onto it."

        .byte   0x0D, 0x0A

        .byte   0x0D, 0x0A, 0

        .locate 512-2

sign:

        .byte   0x55, 0xAA