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[/] [eco32/] [tags/] [eco32-0.23/] [stdalone/] [mkpart/] [mkmboot/] [stage1/] [mbr.s] - Rev 168
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; ; mbr.s -- the master 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. ; ; The boot manager, which is loaded by this code, ; must be in standalone (headerless) executable ; format, stored at absolute disk sectors 2..31, ; and gets loaded and started at 0xC0011000. .set stacktop,0xC0011000 ; top of stack .set loadaddr,0xC0011000 ; where to load the boot manager .set cout,0xC0000018 ; the monitor's console output .set dskio,0xC0000030 ; the monitor's disk I/O ; load the boot manager and start it start: add $29,$0,stacktop ; setup stack add $4,$0,strtmsg ; say what is going on jal msgout add $4,$0,2 ; start loading with sector 2 add $5,$0,loadaddr ; where to load the boot manager and $5,$5,0x3FFFFFFF ; convert to physical address add $6,$0,30 ; 30 sectors to load jal rdsct add $8,$0,loadaddr ; start executing the boot manager jr $8 ; read disk sectors ; $4 start sector number (disk or partition relative) ; $5 transfer address ; $6 number of sectors rdsct: sub $29,$29,32 stw $31,$29,20 stw $6,$29,16 ; sector count add $7,$5,$0 ; transfer address add $6,$4,$17 ; relative sector -> absolute add $5,$0,'r' ; command add $4,$0,$16 ; disk number add $8,$0,dskio jalr $8 bne $2,$0,rderr ; error? ldw $31,$29,20 add $29,$29,32 jr $31 ; disk read error rderr: add $4,$0,dremsg 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 "MBR executing...", 0x0D, 0x0A, 0 dremsg: .byte "disk read error", 0x0D, 0x0A, 0 hltmsg: .byte "bootstrap halted", 0x0D, 0x0A, 0 ; boot record signature .locate 512-2 .byte 0x55, 0xAA
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