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https://opencores.org/ocsvn/eco32/eco32/trunk
Subversion Repositories eco32
[/] [eco32/] [trunk/] [disk/] [tools/] [fs-EOS32/] [mkpboot/] [pbr.s] - Rev 317
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; ; pbr.s -- the partition boot record ; ; Runtime environment: ; ; This code must be loaded and started at 0xC0010000. ; It allocates a stack from 0xC0011000 downwards. So ; it must run within 4K (code + data + stack). ; ; This code expects the disk number of the boot disk ; in $16, the start sector of the disk or partition ; to be booted in $17 and its size in $18. ; ; NOTE: THIS IS A FAKE PARTITION BOOT RECORD! ; It doesn't load anything, but displays a message ; where the real thing can be downloaded from. .set stacktop,0xC0011000 ; top of stack .set cout,0xC0000020 ; the monitor's console output ; display a message and halt start: add $29,$0,stacktop ; setup stack add $4,$0,strtmsg ; say what is going on jal msgout j halt ; output message ; $4 pointer to string msgout: sub $29,$29,8 stw $31,$29,4 stw $16,$29,0 add $16,$4,0 ; $16: pointer to string msgout1: ldbu $4,$16,0 ; get character beq $4,$0,msgout2 ; done? jal chrout ; output character add $16,$16,1 ; bump pointer j msgout1 ; continue msgout2: ldw $16,$29,0 ldw $31,$29,4 add $29,$29,8 jr $31 ; output character ; $4 character chrout: sub $29,$29,4 stw $31,$29,0 add $8,$0,cout jalr $8 ldw $31,$29,0 add $29,$29,4 jr $31 ; halt execution by looping halt: add $4,$0,hltmsg jal msgout halt1: j halt1 ; messages strtmsg: .byte 0x0D, 0x0A .byte "You didn't expect this tiny program to be" .byte 0x0D, 0x0A .byte "a full-fledged operating system, did you?" .byte 0x0D, 0x0A .byte "You can find the real EOS32 for ECO32 on" .byte 0x0D, 0x0A .byte "GitHub, under the name 'eos32-on-eco32'." .byte 0x0D, 0x0A, 0x0D, 0x0A, 0 hltmsg: .byte "bootstrap halted", 0x0D, 0x0A, 0 ; boot record signature .locate 512-2 .byte 0x55, 0xAA
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