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https://opencores.org/ocsvn/eco32/eco32/trunk
Subversion Repositories eco32
[/] [eco32/] [trunk/] [stdalone/] [wrtmbr/] [mbr/] [mbr.s] - Rev 102
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; ; mbr.s -- the master boot record ; .set tba,0xF0300000 ; terminal base address .set tos,0xC0001000 ; top of stack start: add $29,$0,tos ; set stackpointer jal msgout ; output message stop: j stop ; halt by looping msgout: sub $29,$29,8 ; allocate stack frame stw $31,$29,0 ; save return register stw $16,$29,4 ; save local variable add $16,$0,msg ; pointer to string loop: ldbu $4,$16,0 ; get char beq $4,$0,exit ; null - finished jal out ; output char add $16,$16,1 ; bump pointer j loop ; next char exit: ldw $31,$29,0 ; restore return register ldw $16,$29,4 ; restore local variable add $29,$29,8 ; release stack frame jr $31 ; return out: add $8,$0,tba ; set I/O base address out1: ldw $9,$8,8 ; get xmtr status and $9,$9,1 ; xmtr ready? beq $9,$0,out1 ; no - wait stw $4,$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 "Execution halted." .byte 0x0D, 0x0A .byte 0x0D, 0x0A, 0 .locate 512-2 sign: .byte 0x55, 0xAA
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