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