/* *  Partition Boot Sector. Loaded at 0x7C00: *	8a pbsraw.s; 8l -o pbsraw -l -H3 -T0x7C00 pbsraw.8 * Will load the target at LOADSEG*16+LOADOFF, so the target * should be probably be loaded with LOADOFF added to the * -Taddress. * If LOADSEG is a multiple of 64KB and LOADOFF is 0 then * targets larger than 64KB can be loaded. * * This code is uses Enhanced BIOS Services for Disc Drives and * can be used with discs up to 137GB in capacity. * * It relies on the _startlba,  _filesz and _sectsz containing the start lba of * the loader and filesz to contain the size of the file and the sector size. * The sector size can be probably detected by the bios. */#include "x16.h" #define LOADSEG		(0x10000/16)	/* where to load code (64KB) */#define LOADOFF		0 /* * Data is kept on the stack, indexed by rBP. */#define Xdap		0x00		/* disc address packet */#define Xrootsz		0x10		/* file data area */#define Xdrive		0x12		/* boot drive, passed by BIOS or MBR */#define Xtotal		0x14		/* sum of allocated data above */ TEXT _magic(SB), $0	BYTE $0xEB; BYTE $0x3C;		/* jmp .+ 0x3C  (_start0x3E) */	BYTE $0x90			/* nop */TEXT _startlba(SB), $0	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00TEXT _filesz(SB), $0	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00TEXT _sectsz(SB), $0	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00TEXT _pad(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	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00	BYTE $0x00; BYTE $0x00; BYTE $0x00; 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 */ 	/* booting from a CD 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)) 	LBI(0x41, rAH)			/* check extensions present */	LWI(0x55AA, rBX)	LXB(Xdrive, xBP, rDL)		/* drive */	BIOSCALL(0x13)			/* CF set on failure */	JCS _jmp00	CMPI(0xAA55, rBX)	JNE _jmp00	ANDI(0x0001, rCX)	JNE _jmp01 _jmp00:	CALL16(buggery(SB)) _jmp01:	SBPWI(0x0010, Xdap+0)		/* reserved + packet size */	SBPW(rCX, Xdap+2)		/* reserved + # of blocks to transfer */ 	DEC(rCX)	SBPW(rCX, Xdap+12)	SBPW(rCX, Xdap+14) 	CALL16(dreset(SB)) _jmp02:	CLR(rBX)			/* a handy value */ 	LW(_startlba(SB), rAX)	LW(_startlba+2(SB), rDX)	CALL16(printDXAX(SB))	PUSHR(rAX)	PUSHR(rDX)	LW(_filesz(SB), rAX)	LW(_filesz+2(SB), rDX)	CALL16(printDXAX(SB)) 	MW(rAX, rCX)	POPR(rDX)	POPR(rAX) 	LWI(LOADSEG, rBX)		/* address to load into (seg+offset) */	MTSR(rBX, rES)			/*  seg */	LWI(LOADOFF, rBX)		/*  offset */ _readboot:	CALL16(BIOSread(SB))		/* read the sector */ 	LW(_sectsz(SB), rDI)		/* bump addresses/counts */	ADD(rDI, rBX)	JCC _incsecno 	MFSR(rES, rDI)			/* next 64KB segment */	ADDI(0x1000, rDI)	MTSR(rDI, rES) _incsecno:	CLR(rDI)	INC(rAX)	ADC(rDI, rDX)	LOOP _readboot 	LWI(LOADSEG, rDI)		/* set rDS for loaded code */	MTSR(rDI, rDS)	FARJUMP16(LOADSEG, LOADOFF)	/* no deposit, no return */ TEXT buggery(SB), $0	LWI(error(SB), rSI)	CALL16(BIOSputs(SB)) _wait:	CLR(rAX)			/* wait for almost any key */	BIOSCALL(0x16) _reset:	CLR(rBX)			/* set ES segment for BIOS area */	MTSR(rBX, rES) 	LWI(0x0472, rBX)		/* warm-start code address */	LWI(0x1234, rAX)		/* warm-start code */	POKEW				/* MOVW	AX, ES:[BX] */ 	FARJUMP16(0xFFFF, 0x0000)	/* reset */ /* * Read a sector from a disc. On entry: *   rDX:rAX	sector number *   rES:rBX	buffer address */TEXT BIOSread(SB), $0	LWI(5, rDI)			/* retry count (ATAPI ZIPs suck) */_retry:	PUSHA				/* may be trashed by BIOSCALL */ 	SBPW(rBX, Xdap+4)		/* transfer buffer :offset */	MFSR(rES, rDI)			/* transfer buffer seg: */	SBPW(rDI, Xdap+6)	SBPW(rAX, Xdap+8)		/* LBA (64-bits) */	SBPW(rDX, Xdap+10) 	MW(rBP, rSI)			/* disk address packet */	LBI(0x42, rAH)			/* extended read */	LBPB(Xdrive, rDL)		/* form drive */	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 _wait _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	PUSHR(rAX)	PUSHR(rBX)	PUSHR(rCX)	PUSHR(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)) 	POPR(rDI)	POPR(rCX)	POPR(rBX)	POPR(rAX) 	CALL16(printspace(SB))	RET TEXT printDXAX(SB), $0	PUSHR(rAX)	MW(rDX, rAX)	CALL16(printAX(SB))	POPR(rAX)	CALL16(printAX(SB))	RET TEXT printBX(SB), $0	PUSHR(rAX)	MW(rBX, rAX)	CALL16(printAX(SB))	POPR(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'; /* "PBSR..." */TEXT confidence(SB), $0	BYTE $'P'; BYTE $'B'; BYTE $'S'; BYTE $'R';	BYTE $'.'; BYTE $'.'; BYTE $'.';	BYTE $'\z';