ref: aa4cf3a4b23b4a06b2c67c18957f0574aa37df8b
dir: /os/boot.original/pc/pbsdisk.s/
/* * Debugging boot sector. Reads the first directory * sector from disk and displays it. * * It relies on the _volid field in the FAT header containing * the LBA of the root directory. */ #include "x16.h" #define DIROFF 0x00200 /* where to read the root directory (offset) */ #define LOADSEG (0x10000/16) /* where to load code (64KB) */ #define LOADOFF 0 /* * FAT directory entry. */ #define Dname 0x00 #define Dext 0x08 #define Dattr 0x0B #define Dtime 0x16 #define Ddate 0x18 #define Dstart 0x1A #define Dlengthlo 0x1C #define Dlengthhi 0x1E #define Dirsz 0x20 /* * We keep data on the stack, indexed by rBP. */ #define Xdrive 0x00 /* boot drive, passed by BIOS in rDL */ #define Xrootlo 0x02 /* offset of root directory */ #define Xroothi 0x04 #define Xrootsz 0x06 /* file data area */ #define Xtotal 0x08 /* sum of allocated data above */ #define Xdap 0x00 /* disc address packet */ TEXT _magic(SB), $0 BYTE $0xEB; BYTE $0x3C; /* jmp .+ 0x3C (_start0x3E) */ 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; TEXT _driveno(SB), $0 BYTE $0x00 TEXT _reserved0(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; _start0x3E: CLI CLR(rAX) MTSR(rAX, rSS) /* 0000 -> rSS */ MTSR(rAX, rDS) /* 0000 -> rDS, source segment */ MTSR(rAX, rES) LWI(_magic-Xtotal(SB), rSP) MW(rSP, rBP) /* set the indexed-data pointer */ SBPB(rDL, Xdrive) /* save the boot drive */ /* VMware starts us at 7C0:0. Move to 0:7C00 */ PUSHR(rAX) LWI(_nxt(SB), rAX) PUSHR(rAX) BYTE $0xCB /* FAR RET */ TEXT _nxt(SB), $0 STI LWI(confidence(SB), rSI) /* for that warm, fuzzy feeling */ CALL16(BIOSputs(SB)) CALL16(dreset(SB)) _jmp00: LW(_volid(SB), rAX) /* Xrootlo */ LW(_volid+2(SB), rDX) /* Xroothi */ LWI(_magic+DIROFF(SB), rBX) CALL16(BIOSread(SB)) /* read the root directory */ CALL16(printnl(SB)) LWI(_magic+DIROFF(SB), rBX) LWI((512/2), rCX) CALL16(printbuf(SB)) xloop: JMP xloop TEXT buggery(SB), $0 LWI(error(SB), rSI) CALL16(BIOSputs(SB)) TEXT quietbuggery(SB), $0 xbuggery: JMP xbuggery /* * Read a sector from a disc. On entry: * rDX:rAX sector number * rES:rBX buffer address * For BIOSCALL(0x13): * rAH 0x02 * rAL number of sectors to read (1) * rCH low 8 bits of cylinder * rCL high 2 bits of cylinder (7-6), sector (5-0) * rDH head * rDL drive * rES:rBX buffer address */ TEXT BIOSread(SB), $0 LWI(5, rDI) /* retry count (ATAPI ZIPs suck) */ _retry: PUSHA /* may be trashed by BIOSCALL */ PUSHR(rBX) LW(_trksize(SB), rBX) LW(_nheads(SB), rDI) IMUL(rDI, rBX) OR(rBX, rBX) JZ _ioerror _okay: DIV(rBX) /* cylinder -> rAX, track,sector -> rDX */ MW(rAX, rCX) /* save cylinder */ ROLI(0x08, rCX) /* swap rC[HL] */ SHLBI(0x06, rCL) /* move high bits up */ MW(rDX, rAX) CLR(rDX) LW(_trksize(SB), rBX) DIV(rBX) /* head -> rAX, sector -> rDX */ INC(rDX) /* sector numbers are 1-based */ ANDI(0x003F, rDX) /* should not be necessary */ OR(rDX, rCX) MW(rAX, rDX) SHLI(0x08, rDX) /* form head */ LBPB(Xdrive, rDL) /* form drive */ POPR(rBX) LWI(0x0201, rAX) /* form command and sectors */ BIOSCALL(0x13) /* CF set on failure */ JCC _BIOSreadret POPA DEC(rDI) /* too many retries? */ JEQ _ioerror CALL16(dreset(SB)) JMP _retry _ioerror: LWI(ioerror(SB), rSI) CALL16(BIOSputs(SB)) JMP xbuggery _BIOSreadret: POPA RET TEXT dreset(SB), $0 PUSHA CLR(rAX) /* rAH == 0 == reset disc system */ LBPB(Xdrive, rDL) BIOSCALL(0x13) ORB(rAH, rAH) /* status (0 == success) */ POPA JNE _ioerror RET TEXT printsharp(SB), $0 LWI(sharp(SB), rSI) _doprint: CALL16(BIOSputs(SB)) RET TEXT printspace(SB), $0 LWI(space(SB), rSI) JMP _doprint TEXT printnl(SB), $0 LWI(nl(SB), rSI) JMP _doprint /* * Output a string to the display. * String argument is in rSI. */ TEXT BIOSputs(SB), $0 PUSHA CLR(rBX) _BIOSputs: LODSB ORB(rAL, rAL) JEQ _BIOSputsret LBI(0x0E, rAH) BIOSCALL(0x10) JMP _BIOSputs _BIOSputsret: POPA RET /* * Output a register to the display. */ TEXT printAX(SB), $0 PUSHW(rAX) PUSHW(rBX) PUSHW(rCX) PUSHW(rDI) LWI(4, rCX) LWI(numbuf+4(SB), rSI) _nextchar: DEC(rSI) MW(rAX, rBX) ANDI(0x000F, rBX) ADDI(0x30, rBX) /* 0x30 = '0' */ CMPI(0x39, rBX) /* 0x39 = '9' */ JLE _dowrite ADDI(0x07, rBX) /* 0x07 = 'A'-(1+'9')*/ _dowrite: SXB(rBL, 0, xSI) SHRI(4, rAX) DEC(rCX) JNE _nextchar LWI(numbuf(SB), rSI) CALL16(BIOSputs(SB)) POPW(rDI) POPW(rCX) POPW(rBX) POPW(rAX) CALL16(printspace(SB)) RET TEXT printDXAX(SB), $0 PUSHW(rAX) MW(rDX, rAX) CALL16(printAX(SB)) POPW(rAX) CALL16(printAX(SB)) RET TEXT printBX(SB), $0 PUSHW(rAX) MW(rBX, rAX) CALL16(printAX(SB)) POPW(rAX) RET /* * Output some number of words to the display * rDS:rDI - buffer * rCX: number of words */ TEXT printbuf(SB), $0 PUSHW(rAX) PUSHW(rBX) PUSHW(rCX) _nextword: LXW(0, xBX, rAX) CALL16(printAX(SB)) INC(rBX) INC(rBX) DEC(rCX) JNE _nextword POPW(rCX) POPW(rBX) POPW(rAX) RET TEXT error(SB), $0 BYTE $'E'; TEXT ioerror(SB), $0 BYTE $'I'; TEXT nl(SB), $0 BYTE $'\r'; BYTE $'\n'; BYTE $'\z'; TEXT numbuf(SB), $0 BYTE $'X'; BYTE $'X'; BYTE $'X'; BYTE $'X'; BYTE $'\z'; TEXT space(SB), $0 BYTE $' '; BYTE $'\z'; TEXT sharp(SB), $0 BYTE $'#'; BYTE $'\z'; TEXT confidence(SB), $0 BYTE $'P'; BYTE $'\z'