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/*
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* Hard disc boot block. Loaded at 0x7C00, relocates to 0x0600:
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* 8a mbr.s; 8l -o mbr -l -H3 -T0x0600 mbr.8
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*/
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#include "x16.h"
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/*#define FLOPPY 1 /* test on a floppy */
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#define TRACE(C) PUSHA;\
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CLR(rBX);\
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MOVB $C, AL;\
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LBI(0x0E, rAH);\
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BIOSCALL(0x10);\
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POPA
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/*
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* We keep data on the stack, indexed by BP.
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*/
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#define Xdap 0x00 /* disc address packet */
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#define Xtable 0x10 /* partition table entry */
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#define Xdrive 0x12 /* starting disc */
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#define Xtotal 0x14 /* sum of allocated data above */
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/*
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* Start: loaded at 0000:7C00, relocate to 0000:0600.
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* Boot drive is in rDL.
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*/
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TEXT _start(SB), $0
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CLI
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CLR(rAX)
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MTSR(rAX, rSS) /* 0000 -> rSS */
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LWI((0x7C00-Xtotal), rSP) /* 7Bxx -> rSP */
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MW(rSP, rBP) /* set the indexed-data pointer */
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MTSR(rAX, rDS) /* 0000 -> rDS, source segment */
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LWI(0x7C00, rSI) /* 7C00 -> rSI, source offset */
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MTSR(rAX, rES) /* 0000 -> rES, destination segment */
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LWI(0x600, rDI) /* 0600 -> rDI, destination offset */
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LWI(0x100, rCX) /* 0100 -> rCX, loop count (words) */
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CLD
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REP; MOVSL /* MOV DS:[(E)SI] -> ES:[(E)DI] */
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FARJUMP16(0x0000, _start0600(SB))
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TEXT _start0600(SB), $0
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#ifdef FLOPPY
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LBI(0x80, rDL)
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#else
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CLRB(rAL) /* some systems pass 0 */
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CMPBR(rAL, rDL)
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JNE _save
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LBI(0x80, rDL)
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#endif /* FLOPPY */
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_save:
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SXB(rDL, Xdrive, xBP) /* save disc */
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LWI(confidence(SB), rSI) /* for that warm, fuzzy feeling */
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CALL16(BIOSputs(SB))
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LWI(_start+0x01BE(SB), rSI) /* address of partition table */
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LWI(0x04, rCX) /* 4 entries in table */
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LBI(0x80, rAH) /* active entry value */
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CLRB(rAL) /* inactive entry value */
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_activeloop0:
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LXB(0x00, xSI, rBL) /* get active entry from table */
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CMPBR(rBL, rAH) /* is this an active entry? */
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JEQ _active
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CMPBR(rBL, rAL) /* if not active it should be 0 */
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JNE _invalidMBR
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ADDI(0x10, rSI) /* next table entry */
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DEC(rCX)
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JNE _activeloop0
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LWI(noentry(SB), rSI)
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CALL16(buggery(SB))
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_active:
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MW(rSI, rDI) /* save table address */
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_activeloop1:
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ADDI(0x10, rSI) /* next table entry */
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DEC(rCX)
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JEQ _readsector
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LXB(0x00, xSI, rBL) /* get active entry from table */
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CMPBR(rBL, rAH) /* is this an active entry? */
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JNE _activeloop1 /* should only be one active */
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_invalidMBR:
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LWI(invalidMBR(SB), rSI)
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CALL16(buggery(SB))
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_readsector:
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LBI(0x41, rAH) /* check extensions present */
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LWI(0x55AA, rBX)
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LXB(Xdrive, xBP, rDL) /* drive */
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BIOSCALL(0x13) /* CF set on failure */
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JCS _readsector2
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CMPI(0xAA55, rBX)
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JNE _readsector2
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ANDI(0x0001, rCX)
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JEQ _readsector2
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_readsector42:
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SBPBI(0x10, Xdap+0) /* packet size */
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SBPBI(0x00, Xdap+1) /* reserved */
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SBPBI(0x01, Xdap+2) /* number of blocks to transfer */
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SBPBI(0x00, Xdap+3) /* reserved */
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SBPWI(0x7C00, Xdap+4) /* transfer buffer :offset */
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SBPWI(0x0000, Xdap+6) /* transfer buffer seg: */
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LXW(0x08, xDI, rAX) /* LBA (64-bits) */
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SBPW(rAX, Xdap+8)
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LXW(0x0A, xDI, rAX)
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SBPW(rAX, Xdap+10)
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SBPWI(0x0000, Xdap+12)
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SBPWI(0x0000, Xdap+14)
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MW(rBP, rSI) /* disk address packet */
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LBI(0x42, rAH) /* extended read */
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BIOSCALL(0x13) /* CF set on failure */
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JCC _readsectorok
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LWI(ioerror(SB), rSI)
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CALL16(buggery(SB))
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/*
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* Read a sector from a disc using the traditional BIOS call.
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* For BIOSCALL(0x13/AH=0x02):
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* rAH 0x02
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* rAL number of sectors to read (1)
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* rCH low 8 bits of cylinder
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* rCL high 2 bits of cylinder (7-6), sector (5-0)
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* rDH head
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* rDL drive
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* rES:rBX buffer address
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*/
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_readsector2:
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LXB(0x01, xDI, rDH) /* head */
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LXW(0x02, xDI, rCX) /* save active cylinder/sector */
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LWI(0x0201, rAX) /* read one sector */
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LXB(Xdrive, xBP, rDL) /* drive */
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LWI(0x7C00, rBX) /* buffer address (rES already OK) */
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BIOSCALL(0x13) /* CF set on failure */
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JCC _readsectorok
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LWI(ioerror(SB), rSI)
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CALL16(buggery(SB))
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_readsectorok:
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LWI(0x7C00, rBX) /* buffer address (rES already OK) */
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LXW(0x1FE, xBX, rAX)
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CMPI(0xAA55, rAX)
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JNE _bbnotok
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/*
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* Jump to the loaded PBS.
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* rDL and rSI should still contain the drive
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* and partition table pointer respectively.
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*/
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MW(rDI, rSI)
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FARJUMP16(0x0000, 0x7C00)
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_bbnotok:
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LWI(invalidPBS(SB), rSI)
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TEXT buggery(SB), $0
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CALL16(BIOSputs(SB))
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LWI(reboot(SB), rSI)
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CALL16(BIOSputs(SB))
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_wait:
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CLR(rAX) /* wait for any key */
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BIOSCALL(0x16)
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_reset:
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CLR(rBX) /* set ES segment for BIOS area */
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MTSR(rBX, rES)
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LWI(0x0472, rBX) /* warm-start code address */
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LWI(0x1234, rAX) /* warm-start code */
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POKEW /* MOVW AX, ES:[BX] */
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FARJUMP16(0xFFFF, 0x0000) /* reset */
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/*
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* Output a string to the display.
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* String argument is in rSI.
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*/
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TEXT BIOSputs(SB), $0
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PUSHA
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CLR(rBX)
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_BIOSputs:
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LODSB
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ORB(rAL, rAL)
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JEQ _BIOSputsret
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LBI(0x0E, rAH)
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BIOSCALL(0x10)
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JMP _BIOSputs
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_BIOSputsret:
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POPA
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RET
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/* "No active entry in MBR" */
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TEXT noentry(SB), $0
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BYTE $'N'; BYTE $'o'; BYTE $' '; BYTE $'a';
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BYTE $'c'; BYTE $'t'; BYTE $'i'; BYTE $'v';
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BYTE $'e'; BYTE $' '; BYTE $'e'; BYTE $'n';
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BYTE $'t'; BYTE $'r'; BYTE $'y'; BYTE $' ';
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BYTE $'i'; BYTE $'n'; BYTE $' '; BYTE $'M';
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BYTE $'B'; BYTE $'R';
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BYTE $'\z';
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/* "Invalid MBR" */
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TEXT invalidMBR(SB), $0
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BYTE $'I'; BYTE $'n'; BYTE $'v'; BYTE $'a';
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BYTE $'l'; BYTE $'i'; BYTE $'d'; BYTE $' ';
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BYTE $'M'; BYTE $'B'; BYTE $'R';
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BYTE $'\z';
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/* "I/O error" */
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TEXT ioerror(SB), $0
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BYTE $'I'; BYTE $'/'; BYTE $'O'; BYTE $' ';
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BYTE $'e'; BYTE $'r'; BYTE $'r'; BYTE $'o';
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BYTE $'r';
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BYTE $'\z';
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/* "Invalid PBS" */
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TEXT invalidPBS(SB), $0
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BYTE $'I'; BYTE $'n'; BYTE $'v'; BYTE $'a';
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BYTE $'l'; BYTE $'i'; BYTE $'d'; BYTE $' ';
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BYTE $'P'; BYTE $'B'; BYTE $'S';
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BYTE $'\z';
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/* "\r\nPress almost any key to reboot..." */
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TEXT reboot(SB), $0
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BYTE $'\r';BYTE $'\n';
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BYTE $'P'; BYTE $'r'; BYTE $'e'; BYTE $'s';
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BYTE $'s'; BYTE $' '; BYTE $'a'; BYTE $'l';
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BYTE $'m'; BYTE $'o'; BYTE $'s'; BYTE $'t';
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BYTE $' '; BYTE $'a'; BYTE $'n'; BYTE $'y';
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BYTE $' '; BYTE $'k'; BYTE $'e'; BYTE $'y';
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BYTE $' '; BYTE $'t'; BYTE $'o'; BYTE $' ';
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BYTE $'r'; BYTE $'e'; BYTE $'b'; BYTE $'o';
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BYTE $'o'; BYTE $'t'; BYTE $'.'; BYTE $'.';
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BYTE $'.';
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BYTE $'\z';
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/* "MBR..." */
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TEXT confidence(SB), $0
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BYTE $'M'; BYTE $'B'; BYTE $'R'; BYTE $'.';
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BYTE $'.'; BYTE $'.';
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BYTE $'\z';
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