Subversion Repositories planix.SVN

Rev

Details | Last modification | View Log | RSS feed

Rev Author Line No. Line
2 - 1 
/*
2 
 * FAT Partition Boot Sector. Loaded at 0x7C00:
3 
 *	8a pbs.s; 8l -o pbs -l -H3 -T0x7C00 pbs.8
4 
 * Will load the target at LOADSEG*16+LOADOFF, so the target
5 
 * should be probably be loaded with LOADOFF added to the
6 
 * -Taddress.
7 
 * If LOADSEG is a multiple of 64KB and LOADOFF is 0 then
8 
 * targets larger than 64KB can be loaded.
9 
 *
10 
 * This code uses the traditional INT13 BIOS interface and can
11 
 * therefore only access the first 8.4GB of the disc.
12 
 *
13 
 * It relies on the _volid field in the FAT header containing
14 
 * the LBA of the root directory.
15 
 */
16 
#include "x16.h"
17 
 
18 
#define LOADSEG		(0x10000/16)	/* where to load code (64KB) */
19 
#define LOADOFF		0
20 
#define DIROFF		0x0200		/* where to read the root directory */
21 
 
22 
/*
23 
 * FAT directory entry.
24 
 */
25 
#define Dname		0x00
26 
#define Dext		0x08
27 
#define Dattr		0x0B
28 
#define Dtime		0x16
29 
#define Ddate		0x18
30 
#define Dstart		0x1A
31 
#define Dlengthlo	0x1C
32 
#define Dlengthhi	0x1E
33 
 
34 
#define Dirsz		0x20
35 
 
36 
/*
37 
 * Data is kept on the stack, indexed by rBP.
38 
 */
39 
#define Xdap		0x00		/* disc address packet */
40 
#define Xrootsz		0x10		/* file data area */
41 
#define Xdrive		0x12		/* boot drive, passed by BIOS or MBR */
42 
#define Xtotal		0x14		/* sum of allocated data above */
43 
 
44 
TEXT _magic(SB), $0
45 
	BYTE $0xEB; BYTE $0x3C;		/* jmp .+ 0x3C  (_start0x3E) */
46 
	BYTE $0x90			/* nop */
47 
TEXT _version(SB), $0
48 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
49 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
50 
TEXT _sectsize(SB), $0
51 
	BYTE $0x00; BYTE $0x00
52 
TEXT _clustsize(SB), $0
53 
	BYTE $0x00
54 
TEXT _nresrv(SB), $0
55 
	BYTE $0x00; BYTE $0x00
56 
TEXT _nfats(SB), $0
57 
	BYTE $0x00
58 
TEXT _rootsize(SB), $0
59 
	BYTE $0x00; BYTE $0x00
60 
TEXT _volsize(SB), $0
61 
	BYTE $0x00; BYTE $0x00
62 
TEXT _mediadesc(SB), $0
63 
	BYTE $0x00
64 
TEXT _fatsize(SB), $0
65 
	BYTE $0x00; BYTE $0x00
66 
TEXT _trksize(SB), $0
67 
	BYTE $0x00; BYTE $0x00
68 
TEXT _nheads(SB), $0
69 
	BYTE $0x00; BYTE $0x00
70 
TEXT _nhiddenlo(SB), $0
71 
	BYTE $0x00; BYTE $0x00
72 
TEXT _nhiddenhi(SB), $0
73 
	BYTE $0x00; BYTE $0x00;
74 
TEXT _bigvolsize(SB), $0
75 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
76 
TEXT _driveno(SB), $0
77 
	BYTE $0x00
78 
TEXT _reserved0(SB), $0
79 
	BYTE $0x00
80 
TEXT _bootsig(SB), $0
81 
	BYTE $0x00
82 
TEXT _volid(SB), $0
83 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
84 
TEXT _label(SB), $0
85 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
86 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
87 
	BYTE $0x00; BYTE $0x00; BYTE $0x00
88 
TEXT _type(SB), $0
89 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
90 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
91 
 
92 
_start0x3E:
93 
	CLI
94 
	CLR(rAX)
95 
	MTSR(rAX, rSS)			/* 0000 -> rSS */
96 
	MTSR(rAX, rDS)			/* 0000 -> rDS, source segment */
97 
	MTSR(rAX, rES)
98 
	LWI(_magic-Xtotal(SB), rSP)
99 
	MW(rSP, rBP)			/* set the indexed-data pointer */
100 
 
101 
	SBPB(rDL, Xdrive)		/* save the boot drive */
102 
 
103 
	/* booting from a CD starts us at 7C0:0.  Move to 0:7C00 */
104 
	PUSHR(rAX)
105 
	LWI(_nxt(SB), rAX)
106 
	PUSHR(rAX)
107 
	BYTE $0xCB	/* FAR RET */
108 
 
109 
TEXT _nxt(SB), $0
110 
	STI
111 
 
112 
	LWI(confidence(SB), rSI)	/* for that warm, fuzzy feeling */
113 
	CALL16(BIOSputs(SB))
114 
 
115 
	CALL16(dreset(SB))
116 
 
117 
_jmp00:
118 
	LW(_volid(SB), rAX)		/* Xrootlo */
119 
	LW(_volid+2(SB), rDX)		/* Xroothi */
120 
 
121 
	LWI(_magic+DIROFF(SB), rBX)
122 
	CALL16(BIOSread(SB))		/* read the root directory */
123 
 
124 
	LWI((512/Dirsz), rBX)
125 
 
126 
	LWI(_magic+DIROFF(SB), rDI)	/* compare first directory entry */
127 
 
128 
_cmp00:
129 
	PUSHR(rDI)			/* save for later if it matches */
130 
	LWI(bootfile(SB), rSI)
131 
	LWI(Dattr, rCX)
132 
	REP
133 
	CMPSB
134 
	POPR(rDI)
135 
	JEQ _jmp02
136 
 
137 
	DEC(rBX)
138 
	JEQ _jmp01
139 
 
140 
	ADDI(Dirsz, rDI)
141 
	JMP _cmp00
142 
_jmp01:
143 
	CALL16(buggery(SB))
144 
 
145 
_jmp02:
146 
	CLR(rBX)			/* a handy value */
147 
	LW(_rootsize(SB), rAX)		/* calculate and save Xrootsz */
148 
	LWI(Dirsz, rCX)
149 
	MUL(rCX)
150 
	LW(_sectsize(SB), rCX)
151 
	PUSHR(rCX)
152 
	DEC(rCX)
153 
	ADD(rCX, rAX)
154 
	ADC(rBX, rDX)
155 
	POPR(rCX)			/* _sectsize(SB) */
156 
	DIV(rCX)
157 
	PUSHR(rAX)			/* Xrootsz */
158 
 
159 
	/*
160 
	 * rDI points to the matching directory entry.
161 
	 */
162 
	LXW(Dstart, xDI, rAX)		/* starting sector address */
163 
	DEC(rAX)			/* that's just the way it is */
164 
	DEC(rAX)
165 
	LB(_clustsize(SB), rCL)
166 
	CLRB(rCH)
167 
	MUL(rCX)
168 
	LW(_volid(SB), rCX)		/* Xrootlo */
169 
	ADD(rCX, rAX)
170 
	LW(_volid+2(SB), rCX)		/* Xroothi */
171 
	ADC(rCX, rDX)
172 
	POPR(rCX)			/* Xrootsz */
173 
	ADD(rCX, rAX)
174 
	ADC(rBX, rDX)
175 
 
176 
	PUSHR(rAX)			/* calculate how many sectors to read */
177 
	PUSHR(rDX)
178 
	LXW(Dlengthlo, xDI, rAX)
179 
	LXW(Dlengthhi, xDI, rDX)
180 
	LW(_sectsize(SB), rCX)
181 
	PUSHR(rCX)
182 
	DEC(rCX)
183 
	ADD(rCX, rAX)
184 
	ADC(rBX, rDX)
185 
	POPR(rCX)			/* _sectsize(SB) */
186 
	DIV(rCX)
187 
	MW(rAX, rCX)
188 
	POPR(rDX)
189 
	POPR(rAX)
190 
 
191 
	LWI(LOADSEG, rBX)		/* address to load into (seg+offset) */
192 
	MTSR(rBX, rES)			/*  seg */
193 
	LWI(LOADOFF, rBX)		/*  offset */
194 
 
195 
_readboot:
196 
	CALL16(BIOSread(SB))		/* read the sector */
197 
 
198 
	LW(_sectsize(SB), rDI)		/* bump addresses/counts */
199 
	ADD(rDI, rBX)
200 
	JCC _incsecno
201 
 
202 
	MFSR(rES, rDI)			/* next 64KB segment */
203 
	ADDI(0x1000, rDI)
204 
	MTSR(rDI, rES)
205 
 
206 
_incsecno:
207 
	CLR(rDI)
208 
	INC(rAX)
209 
	ADC(rDI, rDX)
210 
	LOOP _readboot
211 
 
212 
	LWI(LOADSEG, rDI)		/* set rDS for loaded code */
213 
	MTSR(rDI, rDS)
214 
	FARJUMP16(LOADSEG, LOADOFF)	/* no deposit, no return */
215 
 
216 
TEXT buggery(SB), $0
217 
	LWI(error(SB), rSI)
218 
	CALL16(BIOSputs(SB))
219 
 
220 
_wait:
221 
	CLR(rAX)			/* wait for almost any key */
222 
	BIOSCALL(0x16)
223 
 
224 
_reset:
225 
	CLR(rBX)			/* set ES segment for BIOS area */
226 
	MTSR(rBX, rES)
227 
 
228 
	LWI(0x0472, rBX)		/* warm-start code address */
229 
	LWI(0x1234, rAX)		/* warm-start code */
230 
	POKEW				/* MOVW	AX, ES:[BX] */
231 
 
232 
	FARJUMP16(0xFFFF, 0x0000)	/* reset */
233 
 
234 
/*
235 
 * Read a sector from a disc. On entry:
236 
 *   rDX:rAX	sector number
237 
 *   rES:rBX	buffer address
238 
 * For BIOSCALL(0x13):
239 
 *   rAH	0x02
240 
 *   rAL	number of sectors to read (1)
241 
 *   rCH	low 8 bits of cylinder
242 
 *   rCL	high 2 bits of cylinder (7-6), sector (5-0)
243 
 *   rDH	head
244 
 *   rDL	drive
245 
 *   rES:rBX	buffer address
246 
 */
247 
TEXT BIOSread(SB), $0
248 
	LWI(5, rDI)			/* retry count (ATAPI ZIPs suck) */
249 
_retry:
250 
	PUSHA				/* may be trashed by BIOSCALL */
251 
	PUSHR(rBX)
252 
 
253 
	LW(_trksize(SB), rBX)
254 
	LW(_nheads(SB), rDI)
255 
	IMUL(rDI, rBX)
256 
	OR(rBX, rBX)
257 
	JZ _ioerror
258 
 
259 
_okay:
260 
	DIV(rBX)			/* cylinder -> rAX, track,sector -> rDX */
261 
 
262 
	MW(rAX, rCX)			/* save cylinder */
263 
	ROLI(0x08, rCX)			/* swap rC[HL] */
264 
	SHLBI(0x06, rCL)		/* move high bits up */
265 
 
266 
	MW(rDX, rAX)
267 
	CLR(rDX)
268 
	LW(_trksize(SB), rBX)
269 
 
270 
	DIV(rBX)			/* head -> rAX, sector -> rDX */
271 
 
272 
	INC(rDX)			/* sector numbers are 1-based */
273 
	ANDI(0x003F, rDX)		/* should not be necessary */
274 
	OR(rDX, rCX)
275 
 
276 
	MW(rAX, rDX)
277 
	SHLI(0x08, rDX)			/* form head */
278 
	LBPB(Xdrive, rDL)		/* form drive */
279 
 
280 
	POPR(rBX)
281 
	LWI(0x0201, rAX)		/* form command and sectors */
282 
	BIOSCALL(0x13)			/* CF set on failure */
283 
	JCC _BIOSreadret
284 
 
285 
	POPA
286 
	DEC(rDI)			/* too many retries? */
287 
	JEQ _ioerror
288 
 
289 
	CALL16(dreset(SB))
290 
	JMP _retry
291 
 
292 
_ioerror:
293 
	LWI(ioerror(SB), rSI)
294 
	CALL16(BIOSputs(SB))
295 
	JMP _wait
296 
 
297 
_BIOSreadret:
298 
	POPA
299 
	RET
300 
 
301 
TEXT dreset(SB), $0
302 
	PUSHA
303 
	CLR(rAX)			/* rAH == 0 == reset disc system */
304 
	LBPB(Xdrive, rDL)
305 
	BIOSCALL(0x13)
306 
	ORB(rAH, rAH)			/* status (0 == success) */
307 
	POPA
308 
	JNE _ioerror
309 
	RET
310 
 
311 
/*
312 
 * Output a string to the display.
313 
 * String argument is in rSI.
314 
 */
315 
TEXT BIOSputs(SB), $0
316 
	PUSHA
317 
	CLR(rBX)
318 
_BIOSputs:
319 
	LODSB
320 
	ORB(rAL, rAL)
321 
	JEQ _BIOSputsret
322 
 
323 
	LBI(0x0E, rAH)
324 
	BIOSCALL(0x10)
325 
	JMP _BIOSputs
326 
 
327 
_BIOSputsret:
328 
	POPA
329 
	RET
330 
 
331 
/* "Bad format or I/O error\r\nPress almost any key to reboot..."*/
332 
TEXT error(SB), $0
333 
	BYTE $'B'; BYTE $'a'; BYTE $'d'; BYTE $' ';
334 
	BYTE $'f'; BYTE $'o'; BYTE $'r'; BYTE $'m';
335 
	BYTE $'a'; BYTE $'t'; BYTE $' '; BYTE $'o';
336 
	BYTE $'r'; BYTE $' ';
337 
/* "I/O error\r\nPress almost any key to reboot..." */
338 
TEXT ioerror(SB), $0
339 
	BYTE $'I'; BYTE $'/'; BYTE $'O'; BYTE $' ';
340 
	BYTE $'e'; BYTE $'r'; BYTE $'r'; BYTE $'o';
341 
	BYTE $'r'; BYTE $'\r';BYTE $'\n';
342 
	BYTE $'P'; BYTE $'r'; BYTE $'e'; BYTE $'s';
343 
	BYTE $'s'; BYTE $' '; BYTE $'a'; BYTE $' ';
344 
	BYTE $'k'; BYTE $'e'; BYTE $'y';
345 
	BYTE $' '; BYTE $'t'; BYTE $'o'; BYTE $' ';
346 
	BYTE $'r'; BYTE $'e'; BYTE $'b'; BYTE $'o';
347 
	BYTE $'o'; BYTE $'t';
348 
	BYTE $'.'; BYTE $'.'; BYTE $'.';
349 
	BYTE $'\z';
350 
 
351 
#ifdef USEBCOM
352 
/* "B       COM" */
353 
TEXT bootfile(SB), $0
354 
	BYTE $'B'; BYTE $' '; BYTE $' '; BYTE $' ';
355 
	BYTE $' '; BYTE $' '; BYTE $' '; BYTE $' ';
356 
	BYTE $'C'; BYTE $'O'; BYTE $'M';
357 
	BYTE $'\z';
358 
#else
359 
/* "9LOAD      " */
360 
TEXT bootfile(SB), $0
361 
	BYTE $'9'; BYTE $'L'; BYTE $'O'; BYTE $'A';
362 
	BYTE $'D'; BYTE $' '; BYTE $' '; BYTE $' ';
363 
	BYTE $' '; BYTE $' '; BYTE $' ';
364 
	BYTE $'\z';
365 
#endif /* USEBCOM */
366 
 
367 
/* "PBS..." */
368 
TEXT confidence(SB), $0
369 
	BYTE $'P'; BYTE $'B'; BYTE $'S'; BYTE $'1';
370 
	BYTE $'.'; BYTE $'.'; BYTE $'.';
371 
	BYTE $'\z';