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#include "x16.h"
#include "mem.h"
#define RELOC 0x7c00
TEXT _magic(SB), $0
BYTE $0xEB; BYTE $0x58; /* jmp .+ 0x58 (_start0x5A) */
BYTE $0x90 /* nop */
TEXT _version(SB), $0
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
TEXT _sectsize(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _clustsize(SB), $0
BYTE $0x00
TEXT _nresrv(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _nfats(SB), $0
BYTE $0x00
TEXT _rootsize(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _volsize(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _mediadesc(SB), $0
BYTE $0x00
TEXT _fatsize(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _trksize(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _nheads(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _nhiddenlo(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _nhiddenhi(SB), $0
BYTE $0x00; BYTE $0x00;
TEXT _bigvolsize(SB), $0
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
/* FAT32 structure, starting @0x24 */
TEXT _fatsz32lo(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _fatsz32hi(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _extflags(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _fsver(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _rootclust(SB), $0
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
TEXT _fsinfo(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _bkboot(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _reserved0(SB), $0
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
TEXT _driveno(SB), $0
BYTE $0x00
TEXT _reserved1(SB), $0
BYTE $0x00
TEXT _bootsig(SB), $0
BYTE $0x00
TEXT _volid(SB), $0
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
TEXT _label(SB), $0
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
BYTE $0x00; BYTE $0x00; BYTE $0x00
TEXT _type(SB), $0
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
_start0x5A:
CLI
CLR(rAX)
MTSR(rAX, rSS) /* 0000 -> rSS */
MTSR(rAX, rDS) /* 0000 -> rDS, source segment */
MTSR(rAX, rES)
LWI(0x100, rCX)
LWI(RELOC, rSI)
MW(rSI, rSP)
LWI(_magic(SB), rDI)
CLD
REP; MOVSL /* MOV DS:[(E)SI] -> ES:[(E)DI] */
MW(rSP, rBP)
PUSHR(rCX)
PUSHI(start16(SB))
BYTE $0xCB /* FAR RET */
TEXT start16(SB), $0
STI
LWI(hello(SB), rSI)
CALL16(print16(SB))
STB(rDL, _driveno(SB))
CLR(rDX)
LW(_fatsize(SB), rAX)
CLR(rCX)
LB(_nfats(SB), rCL)
MUL(rCX)
OR(rAX, rAX)
JNE _fatszok /* zero? it's FAT32 */
LW(_fatsz32hi(SB), rBX)
IMUL(rCX, rBX)
LW(_fatsz32lo(SB), rAX)
MUL(rCX)
ADD(rBX, rDX)
_fatszok:
LW(_nhiddenlo(SB), rCX)
ADD(rCX, rAX)
LW(_nhiddenhi(SB), rCX)
ADC(rCX, rDX)
CLR(rBX)
LW(_nresrv(SB), rCX)
ADD(rCX, rAX)
ADC(rDX, rBX)
SW(rAX, _volid(SB)) /* save for later use */
SW(rBX, _volid+2(SB))
PUSHR(rBP)
LW(_sectsize(SB), rCX)
SUB(rCX, rSP)
MW(rSP, rBP)
MW(rSP, rSI)
_nextsect:
CALL16(readsect16(SB))
LW(_sectsize(SB), rCX)
SHRI(5, rCX)
_nextdir:
PUSHR(rCX)
PUSHR(rSI) /* save for later if it matches */
LWI(bootname(SB), rDI)
LW(bootnamelen(SB), rCX)
CLD
REP
CMPSB
POPR(rSI)
POPR(rCX)
JEQ _found
ADDI(0x20, rSI)
LOOP _nextdir
ADDI(1, rAX)
ADC(rCX, rBX)
JMP _nextsect
_found:
CLR(rBX)
LW(_rootsize(SB), rAX) /* calculate and save Xrootsz */
LWI(0x20, rCX)
MUL(rCX)
LW(_sectsize(SB), rCX)
DEC(rCX)
ADD(rCX, rAX)
ADC(rBX, rDX)
INC(rCX)
DIV(rCX)
PUSHR(rAX) /* Xrootsz */
CLR(rCX)
LXW(0x1a, xSI, rAX) /* start cluster low */
LXW(0x14, xSI, rBX) /* start cluster high */
SUBI(2, rAX) /* cluster -= 2 */
SBB(rCX, rBX)
LB(_clustsize(SB), rCL) /* convert to sectors (AX:DX) */
IMUL(rCX, rBX)
MUL(rCX)
ADD(rBX, rDX)
LW(_volid(SB), rCX) /* Xrootlo */
ADD(rCX, rAX)
LW(_volid+2(SB), rCX) /* Xroothi */
ADC(rCX, rDX)
CLR(rBX)
POPR(rCX) /* Xrootsz */
ADD(rCX, rAX)
ADC(rBX, rDX)
PUSHR(rAX) /* calculate how many sectors to read (CX) */
PUSHR(rDX)
LXW(0x1c, xSI, rAX)
LXW(0x1e, xSI, rDX)
LW(_sectsize(SB), rCX)
DEC(rCX)
ADD(rCX, rAX)
ADC(rBX, rDX)
INC(rCX)
DIV(rCX)
MW(rAX, rCX)
POPR(rBX)
POPR(rAX)
LWI(RELOC, rSI)
PUSHR(rSI) /* entry */
_loadnext:
CALL16(readsect16(SB))
LW(_sectsize(SB), rDX)
ADD(rDX, rSI)
CLR(rDX)
ADDI(1, rAX)
ADC(rDX, rBX)
LOOP _loadnext
LWI(ok(SB), rSI)
CALL16(print16(SB))
LB(_driveno(SB), rDL)
CLI
RET
TEXT print16(SB), $0
PUSHA
CLR(rBX)
_printnext:
LODSB
ORB(rAL, rAL)
JEQ _printret
LBI(0x0E, rAH)
BIOSCALL(0x10)
JMP _printnext
_printret:
POPA
RET
/*
* in:
* AX:BX lba32,
* 0000:SI buffer
*/
TEXT readsect16(SB), $0
_retry:
PUSHA
CLR(rDX)
PUSHR(rDX) /* qword lba */
PUSHR(rDX)
PUSHR(rBX)
PUSHR(rAX)
PUSHR(rDX) /* dword buffer */
PUSHR(rSI)
INC(rDX)
PUSHR(rDX) /* word # of sectors */
PUSHI(0x0010) /* byte reserved, byte packet size */
MW(rSP, rSI)
LB(_driveno(SB), rDL)
LWI(0x4200, rAX)
BIOSCALL(0x13)
JCC _readok
LWI((0x0E00|'!'), rAX)
BIOSCALL(0x10)
ADDI(0x10, rSP)
POPA
JMP _retry
_readok:
LWI((0x0E00|'.'), rAX)
BIOSCALL(0x10)
ADDI(0x10, rSP)
POPA
RET
TEXT bootnamelen(SB), $0
WORD $8
TEXT bootname(SB), $0
BYTE $'9'; BYTE $'B'; BYTE $'O'; BYTE $'O';
BYTE $'T'; BYTE $'F'; BYTE $'A'; BYTE $'T';
BYTE $0
TEXT hello(SB), $0
BYTE $'p'; BYTE $'b'; BYTE $'s'; BYTE $0
TEXT ok(SB), $0
BYTE $'o'; BYTE $'k'; BYTE $'\r'; BYTE $'\n';
BYTE $0
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