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/*
2 
 *  Partition Boot Sector. Loaded at 0x7C00:
3 
 *	8a pbsraw.s; 8l -o pbsraw -l -H3 -T0x7C00 pbsraw.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 is uses Enhanced BIOS Services for Disc Drives and
11 
 * can be used with discs up to 137GB in capacity.
12 
 *
13 
 * It relies on the _startlba,  _filesz and _sectsz containing the start lba of
14 
 * the loader and filesz to contain the size of the file and the sector size.
15 
 * The sector size can be probably detected by the bios.
16 
 */
17 
#include "x16.h"
18 
 
19 
#define LOADSEG		(0x10000/16)	/* where to load code (64KB) */
20 
#define LOADOFF		0
21 
 
22 
/*
23 
 * Data is kept on the stack, indexed by rBP.
24 
 */
25 
#define Xdap		0x00		/* disc address packet */
26 
#define Xrootsz		0x10		/* file data area */
27 
#define Xdrive		0x12		/* boot drive, passed by BIOS or MBR */
28 
#define Xtotal		0x14		/* sum of allocated data above */
29 
 
30 
TEXT _magic(SB), $0
31 
	BYTE $0xEB; BYTE $0x3C;		/* jmp .+ 0x3C  (_start0x3E) */
32 
	BYTE $0x90			/* nop */
33 
TEXT _startlba(SB), $0
34 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
35 
TEXT _filesz(SB), $0
36 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
37 
TEXT _sectsz(SB), $0
38 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
39 
TEXT _pad(SB), $0
40 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
41 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
42 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
43 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
44 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
45 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
46 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
47 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
48 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
49 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
50 
	BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
51 
	BYTE $0x00; BYTE $0x00; BYTE $0x00
52 
 
53 
_start0x3E:
54 
	CLI
55 
	CLR(rAX)
56 
	MTSR(rAX, rSS)			/* 0000 -> rSS */
57 
	MTSR(rAX, rDS)			/* 0000 -> rDS, source segment */
58 
	MTSR(rAX, rES)
59 
	LWI(_magic-Xtotal(SB), rSP)
60 
	MW(rSP, rBP)			/* set the indexed-data pointer */
61 
 
62 
	SBPB(rDL, Xdrive)		/* save the boot drive */
63 
 
64 
	/* booting from a CD starts us at 7C0:0.  Move to 0:7C00 */
65 
	PUSHR(rAX)
66 
	LWI(_nxt(SB), rAX)
67 
	PUSHR(rAX)
68 
	BYTE $0xCB			/* FAR RET */
69 
 
70 
TEXT _nxt(SB), $0
71 
	STI
72 
 
73 
	LWI(confidence(SB), rSI)	/* for that warm, fuzzy feeling */
74 
	CALL16(BIOSputs(SB))
75 
 
76 
	LBI(0x41, rAH)			/* check extensions present */
77 
	LWI(0x55AA, rBX)
78 
	LXB(Xdrive, xBP, rDL)		/* drive */
79 
	BIOSCALL(0x13)			/* CF set on failure */
80 
	JCS _jmp00
81 
	CMPI(0xAA55, rBX)
82 
	JNE _jmp00
83 
	ANDI(0x0001, rCX)
84 
	JNE _jmp01
85 
 
86 
_jmp00:
87 
	CALL16(buggery(SB))
88 
 
89 
_jmp01:
90 
	SBPWI(0x0010, Xdap+0)		/* reserved + packet size */
91 
	SBPW(rCX, Xdap+2)		/* reserved + # of blocks to transfer */
92 
 
93 
	DEC(rCX)
94 
	SBPW(rCX, Xdap+12)
95 
	SBPW(rCX, Xdap+14)
96 
 
97 
	CALL16(dreset(SB))
98 
 
99 
_jmp02:
100 
	CLR(rBX)			/* a handy value */
101 
 
102 
	LW(_startlba(SB), rAX)
103 
	LW(_startlba+2(SB), rDX)
104 
	CALL16(printDXAX(SB))
105 
	PUSHR(rAX)
106 
	PUSHR(rDX)
107 
	LW(_filesz(SB), rAX)
108 
	LW(_filesz+2(SB), rDX)
109 
	CALL16(printDXAX(SB))
110 
 
111 
	MW(rAX, rCX)
112 
	POPR(rDX)
113 
	POPR(rAX)
114 
 
115 
	LWI(LOADSEG, rBX)		/* address to load into (seg+offset) */
116 
	MTSR(rBX, rES)			/*  seg */
117 
	LWI(LOADOFF, rBX)		/*  offset */
118 
 
119 
_readboot:
120 
	CALL16(BIOSread(SB))		/* read the sector */
121 
 
122 
	LW(_sectsz(SB), rDI)		/* bump addresses/counts */
123 
	ADD(rDI, rBX)
124 
	JCC _incsecno
125 
 
126 
	MFSR(rES, rDI)			/* next 64KB segment */
127 
	ADDI(0x1000, rDI)
128 
	MTSR(rDI, rES)
129 
 
130 
_incsecno:
131 
	CLR(rDI)
132 
	INC(rAX)
133 
	ADC(rDI, rDX)
134 
	LOOP _readboot
135 
 
136 
	LWI(LOADSEG, rDI)		/* set rDS for loaded code */
137 
	MTSR(rDI, rDS)
138 
	FARJUMP16(LOADSEG, LOADOFF)	/* no deposit, no return */
139 
 
140 
TEXT buggery(SB), $0
141 
	LWI(error(SB), rSI)
142 
	CALL16(BIOSputs(SB))
143 
 
144 
_wait:
145 
	CLR(rAX)			/* wait for almost any key */
146 
	BIOSCALL(0x16)
147 
 
148 
_reset:
149 
	CLR(rBX)			/* set ES segment for BIOS area */
150 
	MTSR(rBX, rES)
151 
 
152 
	LWI(0x0472, rBX)		/* warm-start code address */
153 
	LWI(0x1234, rAX)		/* warm-start code */
154 
	POKEW				/* MOVW	AX, ES:[BX] */
155 
 
156 
	FARJUMP16(0xFFFF, 0x0000)	/* reset */
157 
 
158 
/*
159 
 * Read a sector from a disc. On entry:
160 
 *   rDX:rAX	sector number
161 
 *   rES:rBX	buffer address
162 
 */
163 
TEXT BIOSread(SB), $0
164 
	LWI(5, rDI)			/* retry count (ATAPI ZIPs suck) */
165 
_retry:
166 
	PUSHA				/* may be trashed by BIOSCALL */
167 
 
168 
	SBPW(rBX, Xdap+4)		/* transfer buffer :offset */
169 
	MFSR(rES, rDI)			/* transfer buffer seg: */
170 
	SBPW(rDI, Xdap+6)
171 
	SBPW(rAX, Xdap+8)		/* LBA (64-bits) */
172 
	SBPW(rDX, Xdap+10)
173 
 
174 
	MW(rBP, rSI)			/* disk address packet */
175 
	LBI(0x42, rAH)			/* extended read */
176 
	LBPB(Xdrive, rDL)		/* form drive */
177 
	BIOSCALL(0x13)			/* CF set on failure */
178 
	JCC _BIOSreadret
179 
 
180 
	POPA
181 
	DEC(rDI)			/* too many retries? */
182 
	JEQ _ioerror
183 
 
184 
	CALL16(dreset(SB))
185 
	JMP _retry
186 
 
187 
_ioerror:
188 
	LWI(ioerror(SB), rSI)
189 
	CALL16(BIOSputs(SB))
190 
	JMP _wait
191 
 
192 
_BIOSreadret:
193 
	POPA
194 
	RET
195 
 
196 
TEXT dreset(SB), $0
197 
	PUSHA
198 
	CLR(rAX)			/* rAH == 0 == reset disc system */
199 
	LBPB(Xdrive, rDL)
200 
	BIOSCALL(0x13)
201 
	ORB(rAH, rAH)			/* status (0 == success) */
202 
	POPA
203 
	JNE _ioerror
204 
	RET
205 
 
206 
TEXT printsharp(SB), $0
207 
	LWI(sharp(SB), rSI)
208 
_doprint:
209 
	CALL16(BIOSputs(SB))
210 
	RET
211 
 
212 
TEXT printspace(SB), $0
213 
	LWI(space(SB), rSI)
214 
	JMP _doprint
215 
 
216 
TEXT printnl(SB), $0
217 
	LWI(nl(SB), rSI)
218 
	JMP _doprint
219 
 
220 
/*
221 
 * Output a string to the display.
222 
 * String argument is in rSI.
223 
 */
224 
TEXT BIOSputs(SB), $0
225 
	PUSHA
226 
	CLR(rBX)
227 
_BIOSputs:
228 
	LODSB
229 
	ORB(rAL, rAL)
230 
	JEQ _BIOSputsret
231 
 
232 
	LBI(0x0E, rAH)
233 
	BIOSCALL(0x10)
234 
	JMP _BIOSputs
235 
 
236 
_BIOSputsret:
237 
	POPA
238 
	RET
239 
 
240 
/*
241 
 * Output a register to the display.
242 
 */
243 
TEXT printAX(SB), $0
244 
	PUSHR(rAX)
245 
	PUSHR(rBX)
246 
	PUSHR(rCX)
247 
	PUSHR(rDI)
248 
 
249 
	LWI(4, rCX)
250 
	LWI(numbuf+4(SB), rSI)
251 
 
252 
_nextchar:
253 
	DEC(rSI)
254 
	MW(rAX, rBX)
255 
	ANDI(0x000F, rBX)
256 
	ADDI(0x30, rBX)	/* 0x30 = '0' */
257 
	CMPI(0x39, rBX)	/* 0x39 = '9' */
258 
	JLE _dowrite
259 
	ADDI(0x07, rBX)	/* 0x07 = 'A'-(1+'9')*/
260 
 
261 
_dowrite:
262 
	SXB(rBL, 0, xSI)
263 
	SHRI(4, rAX)
264 
 
265 
	DEC(rCX)
266 
	JNE _nextchar
267 
 
268 
	LWI(numbuf(SB), rSI)
269 
	CALL16(BIOSputs(SB))
270 
 
271 
	POPR(rDI)
272 
	POPR(rCX)
273 
	POPR(rBX)
274 
	POPR(rAX)
275 
 
276 
	CALL16(printspace(SB))
277 
	RET
278 
 
279 
TEXT printDXAX(SB), $0
280 
	PUSHR(rAX)
281 
	MW(rDX, rAX)
282 
	CALL16(printAX(SB))
283 
	POPR(rAX)
284 
	CALL16(printAX(SB))
285 
	RET
286 
 
287 
TEXT printBX(SB), $0
288 
	PUSHR(rAX)
289 
	MW(rBX, rAX)
290 
	CALL16(printAX(SB))
291 
	POPR(rAX)
292 
	RET
293 
 
294 
TEXT error(SB), $0
295 
	BYTE $'E';
296 
 
297 
TEXT ioerror(SB), $0
298 
	BYTE $'I';
299 
 
300 
TEXT nl(SB), $0
301 
	BYTE $'\r';
302 
	BYTE $'\n';
303 
	BYTE $'\z';
304 
 
305 
TEXT numbuf(SB), $0
306 
	BYTE $'X'; BYTE $'X'; BYTE $'X'; BYTE $'X';
307 
	BYTE $'\z';
308 
 
309 
TEXT space(SB), $0
310 
	BYTE $' ';
311 
	BYTE $'\z';
312 
 
313 
TEXT sharp(SB), $0
314 
	BYTE $'#'; BYTE $'\z';
315 
 
316 
/* "PBSR..." */
317 
TEXT confidence(SB), $0
318 
	BYTE $'P'; BYTE $'B'; BYTE $'S'; BYTE $'R';
319 
	BYTE $'.'; BYTE $'.'; BYTE $'.';
320 
	BYTE $'\z';