;
|
;
|
; mbr.s -- the master boot record
|
; mbr.s -- the master boot record
|
;
|
;
|
|
|
; Runtime environment:
|
; Runtime environment:
|
;
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;
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; This code must be loaded and started at 0xC0010000.
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; This code must be loaded and started at 0xC0010000.
|
; It allocates a stack from 0xC0011000 downwards. So
|
; It allocates a stack from 0xC0011000 downwards. So
|
; it must run within 4K (code + data + stack).
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; it must run within 4K (code + data + stack).
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;
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;
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; This code expects the disk number of the boot disk
|
; This code expects the disk number of the boot disk
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; in $16, the start sector of the disk or partition
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; in $16, the start sector of the disk or partition
|
; to be booted in $17 and its size in $18.
|
; to be booted in $17 and its size in $18.
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;
|
;
|
; The boot manager, which is loaded by this code,
|
; The boot manager, which is loaded by this code,
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; must be in standalone (headerless) executable
|
; must be in standalone (headerless) executable
|
; format, stored at absolute disk sectors 2..31,
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; format, stored at absolute disk sectors 2..31,
|
; and gets loaded and started at 0xC0011000.
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; and gets loaded and started at 0xC0011000.
|
|
|
.set stacktop,0xC0011000 ; top of stack
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.set stacktop,0xC0011000 ; top of stack
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.set loadaddr,0xC0011000 ; where to load the boot manager
|
.set loadaddr,0xC0011000 ; where to load the boot manager
|
|
|
.set cout,0xC0000018 ; the monitor's console output
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.set cout,0xC000001C ; the monitor's console output
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.set dskio,0xC0000030 ; the monitor's disk I/O
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.set dskio,0xC0000024 ; the monitor's disk I/O
|
|
|
; load the boot manager and start it
|
; load the boot manager and start it
|
start:
|
start:
|
add $29,$0,stacktop ; setup stack
|
add $29,$0,stacktop ; setup stack
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add $4,$0,strtmsg ; say what is going on
|
add $4,$0,strtmsg ; say what is going on
|
jal msgout
|
jal msgout
|
add $4,$0,2 ; start loading with sector 2
|
add $4,$0,2 ; start loading with sector 2
|
add $5,$0,loadaddr ; where to load the boot manager
|
add $5,$0,loadaddr ; where to load the boot manager
|
and $5,$5,0x3FFFFFFF ; convert to physical address
|
and $5,$5,0x3FFFFFFF ; convert to physical address
|
add $6,$0,30 ; 30 sectors to load
|
add $6,$0,30 ; 30 sectors to load
|
jal rdsct
|
jal rdsct
|
add $8,$0,loadaddr ; start executing the boot manager
|
add $8,$0,loadaddr ; start executing the boot manager
|
jr $8
|
jr $8
|
|
|
; read disk sectors
|
; read disk sectors
|
; $4 start sector number (disk or partition relative)
|
; $4 start sector number (disk or partition relative)
|
; $5 transfer address
|
; $5 transfer address
|
; $6 number of sectors
|
; $6 number of sectors
|
rdsct:
|
rdsct:
|
sub $29,$29,32
|
sub $29,$29,32
|
stw $31,$29,20
|
stw $31,$29,20
|
stw $6,$29,16 ; sector count
|
stw $6,$29,16 ; sector count
|
add $7,$5,$0 ; transfer address
|
add $7,$5,$0 ; transfer address
|
add $6,$4,$17 ; relative sector -> absolute
|
add $6,$4,$17 ; relative sector -> absolute
|
add $5,$0,'r' ; command
|
add $5,$0,'r' ; command
|
add $4,$0,$16 ; disk number
|
add $4,$0,$16 ; disk number
|
add $8,$0,dskio
|
add $8,$0,dskio
|
jalr $8
|
jalr $8
|
bne $2,$0,rderr ; error?
|
bne $2,$0,rderr ; error?
|
ldw $31,$29,20
|
ldw $31,$29,20
|
add $29,$29,32
|
add $29,$29,32
|
jr $31
|
jr $31
|
|
|
; disk read error
|
; disk read error
|
rderr:
|
rderr:
|
add $4,$0,dremsg
|
add $4,$0,dremsg
|
jal msgout
|
jal msgout
|
j halt
|
j halt
|
|
|
; output message
|
; output message
|
; $4 pointer to string
|
; $4 pointer to string
|
msgout:
|
msgout:
|
sub $29,$29,8
|
sub $29,$29,8
|
stw $31,$29,4
|
stw $31,$29,4
|
stw $16,$29,0
|
stw $16,$29,0
|
add $16,$4,0 ; $16: pointer to string
|
add $16,$4,0 ; $16: pointer to string
|
msgout1:
|
msgout1:
|
ldbu $4,$16,0 ; get character
|
ldbu $4,$16,0 ; get character
|
beq $4,$0,msgout2 ; done?
|
beq $4,$0,msgout2 ; done?
|
jal chrout ; output character
|
jal chrout ; output character
|
add $16,$16,1 ; bump pointer
|
add $16,$16,1 ; bump pointer
|
j msgout1 ; continue
|
j msgout1 ; continue
|
msgout2:
|
msgout2:
|
ldw $16,$29,0
|
ldw $16,$29,0
|
ldw $31,$29,4
|
ldw $31,$29,4
|
add $29,$29,8
|
add $29,$29,8
|
jr $31
|
jr $31
|
|
|
; output character
|
; output character
|
; $4 character
|
; $4 character
|
chrout:
|
chrout:
|
sub $29,$29,4
|
sub $29,$29,4
|
stw $31,$29,0
|
stw $31,$29,0
|
add $8,$0,cout
|
add $8,$0,cout
|
jalr $8
|
jalr $8
|
ldw $31,$29,0
|
ldw $31,$29,0
|
add $29,$29,4
|
add $29,$29,4
|
jr $31
|
jr $31
|
|
|
; halt execution by looping
|
; halt execution by looping
|
halt:
|
halt:
|
add $4,$0,hltmsg
|
add $4,$0,hltmsg
|
jal msgout
|
jal msgout
|
halt1:
|
halt1:
|
j halt1
|
j halt1
|
|
|
; messages
|
; messages
|
strtmsg:
|
strtmsg:
|
.byte "MBR executing...", 0x0D, 0x0A, 0
|
.byte "MBR executing...", 0x0D, 0x0A, 0
|
dremsg:
|
dremsg:
|
.byte "disk read error", 0x0D, 0x0A, 0
|
.byte "disk read error", 0x0D, 0x0A, 0
|
hltmsg:
|
hltmsg:
|
.byte "bootstrap halted", 0x0D, 0x0A, 0
|
.byte "bootstrap halted", 0x0D, 0x0A, 0
|
|
|
; boot record signature
|
; boot record signature
|
.locate 512-2
|
.locate 512-2
|
.byte 0x55, 0xAA
|
.byte 0x55, 0xAA
|
|
|
