1 !
2 ! SYS_SIZE is the number of clicks (16 bytes) to be loaded.
3 ! 0x3000 is 0x30000 bytes = 196kB, more than enough for current
4 ! versions of linux
5 !
6 #include <linux/config.h>
7 SYSSIZE = DEF_SYSSIZE
8 !
9 ! bootsect.s (C) 1991 Linus Torvalds
10 ! modified by Drew Eckhardt
11 ! modified by Bruce Evans (bde)
12 !
13 ! bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves
14 ! itself out of the way to address 0x90000, and jumps there.
15 !
16 ! bde - should not jump blindly, there may be systems with only 512K low
17 ! memory. Use int 0x12 to get the top of memory, etc.
18 !
19 ! It then loads 'setup' directly after itself (0x90200), and the system
20 ! at 0x10000, using BIOS interrupts.
21 !
22 ! NOTE! currently system is at most 8*65536 bytes long. This should be no
23 ! problem, even in the future. I want to keep it simple. This 512 kB
24 ! kernel size should be enough, especially as this doesn't contain the
25 ! buffer cache as in minix
26 !
27 ! The loader has been made as simple as possible, and continuos
28 ! read errors will result in a unbreakable loop. Reboot by hand. It
29 ! loads pretty fast by getting whole tracks at a time whenever possible.
30
31 .text
32
33 SETUPSECS = 4 ! nr of setup-sectors
34 BOOTSEG = 0x07C0 ! original address of boot-sector
35 INITSEG = DEF_INITSEG ! we move boot here - out of the way
36 SETUPSEG = DEF_SETUPSEG ! setup starts here
37 SYSSEG = DEF_SYSSEG ! system loaded at 0x10000 (65536).
38 ENDSEG = SYSSEG + SYSSIZE ! where to stop loading
39
40 ! ROOT_DEV & SWAP_DEV are now written by "build".
41 ROOT_DEV = 0
42 SWAP_DEV = 0
43
44 ! ld86 requires an entry symbol. This may as well be the usual one.
45 .globl _main
46 _main:
47 #if 0 /* hook for debugger, harmless unless BIOS is fussy (old HP) */ 48 int 3
49 #endif 50 mov ax,#BOOTSEG
51 mov ds,ax
52 mov ax,#INITSEG
53 mov es,ax
54 mov cx,#256
55 sub si,si
56 sub di,di
57 cld
58 rep
59 movsw
60 jmpi go,INITSEG
61
62 go: mov ax,cs
63 mov dx,#0x4000-12 ! 0x4000 is arbitrary value >= length of
64 ! bootsect + length of setup + room for stack
65 ! 12 is disk parm size
66
67 ! bde - changed 0xff00 to 0x4000 to use debugger at 0x6400 up (bde). We
68 ! wouldn't have to worry about this if we checked the top of memory. Also
69 ! my BIOS can be configured to put the wini drive tables in high memory
70 ! instead of in the vector table. The old stack might have clobbered the
71 ! drive table.
72
73 mov ds,ax
74 mov es,ax
75 push ax
76
77 mov ss,ax ! put stack at INITSEG:0x4000-12.
78 mov sp,dx
79 /* 80 * Many BIOS's default disk parameter tables will not 81 * recognize multi-sector reads beyond the maximum sector number 82 * specified in the default diskette parameter tables - this may 83 * mean 7 sectors in some cases. 84 * 85 * Since single sector reads are slow and out of the question, 86 * we must take care of this by creating new parameter tables 87 * (for the first disk) in RAM. We will set the maximum sector 88 * count to 18 - the most we will encounter on an HD 1.44. 89 * 90 * High doesn't hurt. Low does. 91 * 92 * Segments are as follows: ds=es=ss=cs - INITSEG, 93 * fs = 0, gs = parameter table segment 94 */ 95
96 push #0
97 pop fs
98 mov bx,#0x78 ! fs:bx is parameter table address
99 seg fs
100 lgs si,(bx) ! gs:si is source
101
102 mov di,dx ! es:di is destination
103 mov cx,#6 ! copy 12 bytes
104 cld
105
106 rep
107 seg gs
108 movsw
109
110 mov di,dx
111 movb 4(di),*18 ! patch sector count
112
113 seg fs
114 mov (bx),di
115 seg fs
116 mov 2(bx),es
117
118 pop ax
119 mov fs,ax
120 mov gs,ax
121
122 xor ah,ah ! reset FDC
123 xor dl,dl
124 int 0x13
125
126 ! load the setup-sectors directly after the bootblock.
127 ! Note that 'es' is already set up.
128
129 load_setup:
130 xor dx, dx ! drive 0, head 0
131 mov cx,#0x0002 ! sector 2, track 0
132 mov bx,#0x0200 ! address = 512, in INITSEG
133 mov ax,#0x0200+SETUPSECS ! service 2, nr of sectors
134 ! (assume all on head 0, track 0)
135 int 0x13 ! read it
136 jnc ok_load_setup ! ok - continue
137
138 push ax ! dump error code
139 call print_nl
140 mov bp, sp
141 call print_hex
142 pop ax
143
144 xor dl, dl ! reset FDC
145 xor ah, ah
146 int 0x13
147 jmp load_setup
148
149 ok_load_setup:
150
151 ! Get disk drive parameters, specifically nr of sectors/track
152
153 #if 0
154
155 ! bde - the Phoenix BIOS manual says function 0x08 only works for fixed
156 ! disks. It doesn't work for one of my BIOS's (1987 Award). It was
157 ! fatal not to check the error code.
158
159 xor dl,dl
160 mov ah,#0x08 ! AH=8 is get drive parameters
161 int 0x13
162 xor ch,ch
163 #else 164
165 ! It seems that there is no BIOS call to get the number of sectors. Guess
166 ! 18 sectors if sector 18 can be read, 15 if sector 15 can be read.
167 ! Otherwise guess 9.
168
169 xor dx, dx ! drive 0, head 0
170 mov cx,#0x0012 ! sector 18, track 0
171 mov bx,#0x0200+SETUPSECS*0x200 ! address after setup (es = cs)
172 mov ax,#0x0201 ! service 2, 1 sector
173 int 0x13
174 jnc got_sectors
175 mov cl,#0x0f ! sector 15
176 mov ax,#0x0201 ! service 2, 1 sector
177 int 0x13
178 jnc got_sectors
179 mov cl,#0x09
180
181 #endif 182
183 got_sectors:
184 seg cs
185 mov sectors,cx
186 mov ax,#INITSEG
187 mov es,ax
188
189 ! Print some inane message
190
191 mov ah,#0x03 ! read cursor pos
192 xor bh,bh
193 int 0x10
194
195 mov cx,#9
196 mov bx,#0x0007 ! page 0, attribute 7 (normal)
197 mov bp,#msg1
198 mov ax,#0x1301 ! write string, move cursor
199 int 0x10
200
201 ! ok, we've written the message, now
202 ! we want to load the system (at 0x10000)
203
204 mov ax,#SYSSEG
205 mov es,ax ! segment of 0x010000
206 call read_it
207 call kill_motor
208 call print_nl
209
210 ! After that we check which root-device to use. If the device is
211 ! defined (!= 0), nothing is done and the given device is used.
212 ! Otherwise, either /dev/PS0 (2,28) or /dev/at0 (2,8), depending
213 ! on the number of sectors that the BIOS reports currently.
214
215 seg cs
216 mov ax,root_dev
217 or ax,ax
218 jne root_defined
219 seg cs
220 mov bx,sectors
221 mov ax,#0x0208 ! /dev/ps0 - 1.2Mb
222 cmp bx,#15
223 je root_defined
224 mov ax,#0x021c ! /dev/PS0 - 1.44Mb
225 cmp bx,#18
226 je root_defined
227 undef_root:
228 jmp undef_root
229 root_defined:
230 seg cs
231 mov root_dev,ax
232
233 ! after that (everyting loaded), we jump to
234 ! the setup-routine loaded directly after
235 ! the bootblock:
236
237 jmpi 0,SETUPSEG
238
239 ! This routine loads the system at address 0x10000, making sure
240 ! no 64kB boundaries are crossed. We try to load it as fast as
241 ! possible, loading whole tracks whenever we can.
242 !
243 ! in: es - starting address segment (normally 0x1000)
244 !
245 sread: .word 1+SETUPSECS ! sectors read of current track
246 head: .word 0 ! current head
247 track: .word 0 ! current track
248
249 read_it:
250 mov ax,es
251 test ax,#0x0fff
252 die: jne die ! es must be at 64kB boundary
253 xor bx,bx ! bx is starting address within segment
254 rp_read:
255 mov ax,es
256 cmp ax,#ENDSEG ! have we loaded all yet?
257 jb ok1_read
258 ret
259 ok1_read:
260 seg cs
261 mov ax,sectors
262 sub ax,sread
263 mov cx,ax
264 shl cx,#9
265 add cx,bx
266 jnc ok2_read
267 je ok2_read
268 xor ax,ax
269 sub ax,bx
270 shr ax,#9
271 ok2_read:
272 call read_track
273 mov cx,ax
274 add ax,sread
275 seg cs
276 cmp ax,sectors
277 jne ok3_read
278 mov ax,#1
279 sub ax,head
280 jne ok4_read
281 inc track
282 ok4_read:
283 mov head,ax
284 xor ax,ax
285 ok3_read:
286 mov sread,ax
287 shl cx,#9
288 add bx,cx
289 jnc rp_read
290 mov ax,es
291 add ah,#0x10
292 mov es,ax
293 xor bx,bx
294 jmp rp_read
295
296 read_track:
297 pusha
298 pusha
299 mov ax, #0xe2e ! loading... message 2e = .
300 mov bx, #7
301 int 0x10
302 popa
303
304 mov dx,track
305 mov cx,sread
306 inc cx
307 mov ch,dl
308 mov dx,head
309 mov dh,dl
310 and dx,#0x0100
311 mov ah,#2
312
313 push dx ! save for error dump
314 push cx
315 push bx
316 push ax
317
318 int 0x13
319 jc bad_rt
320 add sp, #8
321 popa
322 ret
323
324 bad_rt: push ax ! save error code
325 call print_all ! ah = error, al = read
326
327
328 xor ah,ah
329 xor dl,dl
330 int 0x13
331
332
333 add sp, #10
334 popa
335 jmp read_track
336
337 /* 338 * print_all is for debugging purposes. 339 * It will print out all of the registers. The assumption is that this is 340 * called from a routine, with a stack frame like 341 * dx 342 * cx 343 * bx 344 * ax 345 * error 346 * ret <- sp 347 * 348 */ 349
350 print_all:
351 mov cx, #5 ! error code + 4 registers
352 mov bp, sp
353
354 print_loop:
355 push cx ! save count left
356 call print_nl ! nl for readability
357
358 cmp cl, 5
359 jae no_reg ! see if register name is needed
360
361 mov ax, #0xe05 + 'A - 1
362 sub al, cl
363 int 0x10
364
365 mov al, #'X
366 int 0x10
367
368 mov al, #':
369 int 0x10
370
371 no_reg:
372 add bp, #2 ! next register
373 call print_hex ! print it
374 pop cx
375 loop print_loop
376 ret
377
378 print_nl:
379 mov ax, #0xe0d ! CR
380 int 0x10
381 mov al, #0xa ! LF
382 int 0x10
383 ret
384
385 /* 386 * print_hex is for debugging purposes, and prints the word 387 * pointed to by ss:bp in hexadecmial. 388 */ 389
390 print_hex:
391 mov cx, #4 ! 4 hex digits
392 mov dx, (bp) ! load word into dx
393 print_digit:
394 rol dx, #4 ! rotate so that lowest 4 bits are used
395 mov ah, #0xe
396 mov al, dl ! mask off so we have only next nibble
397 and al, #0xf
398 add al, #'0 ! convert to 0-based digit
399 cmp al, #'9 ! check for overflow
400 jbe good_digit
401 add al, #'A - '0 - 10
402
403 good_digit:
404 int 0x10
405 loop print_digit
406 ret
407
408
409 /* 410 * This procedure turns off the floppy drive motor, so 411 * that we enter the kernel in a known state, and 412 * don't have to worry about it later. 413 */ 414 kill_motor:
415 push dx
416 mov dx,#0x3f2
417 xor al, al
418 outb
419 pop dx
420 ret
421
422 sectors:
423 .word 0
424
425 msg1:
426 .byte 13,10
427 .ascii "Loading"
428
429 .org 506
430 swap_dev:
431 .word SWAP_DEV
432 root_dev:
433 .word ROOT_DEV
434 boot_flag:
435 .word 0xAA55