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/*
* 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'
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