1 [cpu 286]
2 [bits 16]
3 
4 %include "macros.inc"
5 
6 struc TSS
7 .link:	resw 1	; +0x00
8 .sp0:	resw 1	; +0x02
9 .ss0:	resw 1	; +0x04
10 .sp1:	resw 1	; +0x06
11 .ss1:	resw 1 	; +0x08
12 .sp2:	resw 1 	; +0x0a
13 .ss2:	resw 1 	; +0x0c
14 .ip:	resw 1	; +0x0e
15 .flags:	resw 1	; +0x10
16 .ax:	resw 1	; +0x12
17 .cx:	resw 1	; +0x14
18 .dx:	resw 1	; +0x16
19 .bx:	resw 1	; +0x18
20 .sp:	resw 1	; +0x1a
21 .bp:	resw 1	; +0x1c
22 .si:	resw 1	; +0x1e
23 .di:	resw 1	; +0x20
24 .es:	resw 1	; +0x22
25 .cs:	resw 1	; +0x24
26 .ss:	resw 1	; +0x26
27 .ds:	resw 1	; +0x28
28 .ldtr:	resw 1	; +0x2a
29 .size:		; +0x2c
30 endstruc
31 
32 section .text
33 extern floppy_init
34 global _entry
35 global putchar
36 global puts
37 global puthexb
38 global puthexw
39 global panic
40 _entry:
41 	pop dx
42 	mov byte [bootdrv], dl
43 
44 	; copy user task into 0x2000:0
45 	mov ax, 0x2000
46 	mov es, ax
47 	xor di, di
48 	lea si, [user]
49 	lea cx, [user.end - user]
50 	rep movsb
51 
52 	; clear screen
53 	mov bx, 0xb800
54 	mov es, bx
55 	xor di, di
56 	mov ax, (' ' | (0x07 << 8))
57 	mov cx, (80 * 25 * 2)
58 	rep stosw
59 
60 	; get size of conventional memory (below 640K)
61 	int 0x12
62 	mov word [convmem], ax
63 
64 	; get size of extended memory (above 1M)
65 	mov ah, 0x88
66 	int 0x15
67 	jc .noxm
68 	mov word [highmem], ax
69 
70 .noxm:
71 	; NOTE: BIOS cannot be accessed from here
72 	cli
73 
74 	; disable keyboard
75 	call .wait
76 	mov al, 0xAD
77 	out 0x64, al
78 
79 	; read from input
80 	call .wait
81 	mov al, 0xD0
82 	out 0x64, al
83 	call .wait2
84 	in al, 0x60
85 	mov bl, al
86 
87 	; write to output
88 	call .wait
89 	mov al,0xD1
90 	out 0x64,al
91 	call .wait
92 	mov al, bl
93 	or al, 2	; enable A20 line
94 	out 0x60, al
95 
96 	; enable keyboard
97 	call .wait
98 	mov al, 0xAE
99 	out 0x64, al
100 	call .wait
101 	jmp .setup
102 
103 .wait:
104 	in al,0x64
105 	test al, 2
106 	jnz .wait
107 	ret
108 
109 
110 .wait2:
111 	in      al,0x64
112 	test    al,1
113 	jz      .wait2
114 	ret
115 
116 .setup:
117 	lidt [idtr]
118 	lgdt [gdtr]
119 	smsw ax
120 	or ax, 1
121 	lmsw ax
122 	jmp (gdt.text - gdt):.reloadcs
123 
124 .reloadcs:
125 	lea sp, [stack]
126 	lea ax, [gdt.data - gdt]
127 	mov ds, ax
128 	mov es, ax
129 	mov ss, ax
130 
131 	; initialize PIC
132 	outb_slow 0x20, 0x11	; Start the initialization routine (in cascae mode)
133 	outb_slow 0xA0, 0x11
134 	outb_slow 0x21, 0x20	; Master PIC IRQ offset
135 	outb_slow 0xA1, 0x28	; Slave PIC IRQ offset
136 	outb_slow 0x21, 4	; Tell the master PIC that there is a slave PIC at IRQ2
137 	outb_slow 0xA1, 2	; Tell the slave PIC it's cascade identity
138 	outb_slow 0x21, 1	; Use the 8086-mode (and not the 8088 mode)
139 	outb_slow 0xA1, 1
140 	outb_slow 0x21, 0xfe	; Set the IRQ masks
141 	outb_slow 0xA1, 0xff
142 
143 	; initialize IDT
144 	mov al, 0x20
145 	mov ah, 0x86
146 	lea dx, [i_timer]
147 	call set_irq
148 	mov al, 0x80
149 	mov ah, 0xe6
150 	lea dx, [i_sys]
151 	call set_irq
152 
153 	lea bp, [convmsg]
154 	call puts
155 	mov ax, word [convmem]
156 	call puthexw
157 	lea bp, [kbmsg]
158 	call puts
159 
160 	lea bp, [xmmsg]
161 	call puts
162 	mov ax, word [highmem]
163 	call puthexw
164 	lea bp, [kbmsg]
165 	call puts
166 
167 	call floppy_init
168 
169 	; set up TSS
170 	mov word [tss + TSS.link], 0
171 	mov word [tss + TSS.sp0], stack
172 	mov word [tss + TSS.ss0], (gdt.data - gdt)
173 
174 	; load TSS into TR
175 	lea ax, [gdt.tss - gdt]
176 	ltr ax
177 
178 	; load LDT
179 	lea ax, [gdt.ldt - gdt]
180 	lldt ax
181 
182 	; enter userspace, TODO: enter ring 3
183 	mov ax, 0x0f		; LDT .data
184 	mov ds, ax
185 	mov es, ax
186 	push 0x17		; ss (LDT .stack)
187 	push 0xfffe		; sp
188 	push 0x202		; flags (EI | 0x02)
189 	push 0x07		; cs (LDT .text)
190 	push 0			; ip
191 	iret
192 
193 i_timer:
194 	pusha
195 	push ds
196 	push es
197 
198 	mov ax, (gdt.data - gdt)
199 	mov ds, ax
200 	mov es, ax
201 
202 	mov al, '.'
203 	call putchar
204 	
205 	outb 0x20, 0x20
206 	pop es
207 	pop ds
208 	popa
209 	iret
210 
211 ; ds:si - from
212 ; es:di - to
213 ; cx - count
214 copy_from_user:
215 	rep movsb
216 	ret
217 
218 i_sys:	; syscall interrupt (0x80)
219 	push ds
220 	push es
221 
222 	; load kernel .data into es
223 	push ax
224 	mov ax, (gdt.data - gdt)
225 	mov es, ax
226 	pop ax
227 
228 	test ax, ax
229 	jz .print
230 
231 	; invalid interrupt
232 	mov ax, -1
233 	jmp .ret
234 
235 
236 .print:
237 	push cx
238 	mov si, bx
239 	lea di, [ubuf]
240 	; TODO: check that cx < sizeof(ubuf)
241 	call copy_from_user
242 	pop bx
243 	mov byte [ubuf + bx], 0
244 
245 	; load kernel .data into ds & es
246 	lea ax, [gdt.data - gdt]
247 	mov ds, ax
248 	mov es, ax
249 
250 	lea bp, [ubuf]
251 	call puts
252 	xor ax, ax
253 	jmp .ret
254 
255 .ret:
256 	pop es
257 	pop ds
258 	iret
259 
260 ; al - num
261 ; ah - attr
262 ; dx - offset
263 set_irq:
264 	xor bh, bh
265 	mov bl, al
266 	shl bx, 3
267 	lea bx, [idt + bx]
268 	mov word [bx + 0], dx
269 	mov word [bx + 2], (gdt.text - gdt)
270 	mov byte [bx + 4], 0x00
271 	mov byte [bx + 5], ah
272 	mov word [bx + 6], 0
273 	ret
274 
275 error:
276 	cli
277 	lea bp, [errstr]
278 	call puts
279 	hlt
280 	jmp $
281 
282 ; ax - value
283 puthexw:
284 	push ax
285 	mov al, ah
286 	call puthexb
287 	pop ax
288 	jmp puthexb
289 
290 ; al - value
291 puthexb:
292 	push ax
293 	shr al, 4
294 	call puthexch
295 	pop ax
296 	and al, 0xf
297 	jmp puthexch
298 
299 ; al - hex digit
300 puthexch:
301 	cmp al, 10
302 	jae .hex
303 	add al, '0'
304 	jmp putchar
305 
306 .hex:
307 	add al, 'a' - 10
308 	jmp putchar
309 
310 ; al - char
311 writech:
312 	lea bx, [gdt.vid - gdt]
313 	mov es, bx
314 
315 	xor ch, ch
316 	xor dh, dh
317 	mov cl, byte [posx]
318 	mov dl, byte [posy]
319 
320 	cmp al, 10	; '\n'
321 	je .nl
322 
323 	imul bx, dx, 80
324 	add bx, cx
325 	shl bx, 1
326 	mov byte [es:bx], al
327 	
328 	inc cl
329 	cmp cl, 80
330 	je .nl
331 	mov byte [posx], cl
332 	ret
333 
334 .nl:
335 	mov byte [posx], 0
336 	inc dl
337 
338 	cmp dl, 25
339 	je .scroll
340 	mov byte [posy], dl
341 	ret
342 
343 .scroll:
344 	push ds
345 	mov ax, 0x18
346 	mov ds, ax
347 
348 	cld
349 	xor di, di
350 	mov si, 160
351 	mov cx, 80 * 24
352 	rep movsw
353 
354 	pop ds
355 
356 	mov di, 80 * 24 * 2
357 	mov cx, 80
358 	mov ax, (' ' | (0x07 << 8))
359 	rep stosw
360 	mov byte [posy], 24
361 	ret
362 
363 ; al - ch
364 putchar:
365 	call writech
366 	jmp update_cursor
367 
368 ; bp - str
369 puts:
370 	mov al, byte [ds:bp]
371 	inc bp
372 	test al, al
373 	jz update_cursor
374 
375 	call writech
376 	jmp puts
377 
378 update_cursor:
379 	mov dx, 0x3D4
380 	mov al, 0x0f
381 	out dx, al
382 
383 	mov bx, word [posy]
384 	imul bx, 80
385 	add bx, word [posx]
386 
387 	inc dx		; 0x3D5
388 	mov al, bl
389 	out dx, al
390 
391 	dec dx		; 0x3D4
392 	mov al, 0x0E
393 	out dx, al
394 
395 	inc dx		; 0x3D5
396 	mov al, bh
397 	out dx, al
398 	ret
399 
400 ; bp - str
401 panic:
402 	call puts
403 
404 .halt:
405 	cli
406 	hlt
407 	jmp .halt
408 
409 section .rodata
410 user:
411 	incbin "user.bin"
412 .end:
413 hello:
414 	db "Hello World", 10, 0
415 errstr:
416 	db "Error", 10, 0
417 convmsg:
418 	db "Conventional memory: 0x", 0
419 xmmsg:
420 	db "Extended memory: 0x", 0
421 kbmsg:
422 	db " KB", 10, 0
423 
424 align 2
425 idtr:
426 	dw idt.end - idt - 1
427 	dd idt + 0x10000
428 
429 align 2
430 gdtr:
431 	dw gdt.end - gdt - 1
432 	dd gdt + 0x10000
433 
434 
435 section .data
436 gdt:
437 	dq 0
438 
439 .text:	; 0x08 - kernel code
440 	dw 0xffff
441 	dw 0x0000
442 	db 0x01
443 	db 0x9A
444 	dw 0x0000
445 
446 .data:	; 0x10 - kernel data
447 	dw 0xffff
448 	dw 0x0000
449 	db 0x01
450 	db 0x92
451 	dw 0x0000
452 
453 .vid:	; 0x18 - video memory
454 	dw 4000
455 	dw 0x8000
456 	db 0x0b
457 	db 0x92
458 	dw 0x0000
459 	
460 .tss:	; 0x20 - TSS
461 	dw TSS.size
462 	dw tss
463 	db 0x01
464 	db 0x81
465 	dw 0x0000
466 
467 .ldt:	; 0x28 - LDT
468 	dw (ldt.end - ldt)
469 	dw ldt
470 	db 0x01
471 	db 0x82
472 	dw 0x0000
473 .end:
474 
475 ldt:
476 .text:	; 0x07 - user code
477 	dw 0xffff
478 	dw 0x0000
479 	db 0x02
480 	db 0xfa
481 	dw 0x0000
482 
483 .data:	; 0x0f - user data
484 	dw 0xffff
485 	dw 0x0000
486 	db 0x02
487 	db 0xf2
488 	dw 0x0000
489 
490 .stack:	; 0x17 - user stack
491 	dw 0xffff
492 	dw 0x0000
493 	db 0x03
494 	db 0xf2
495 	dw 0x0000
496 .end:
497 
498 section .bss
499 ubuf:
500 	resb 256
501 posx:
502 	resw 1
503 posy:
504 	resw 1
505 bootdrv:
506 	resb 1
507 convmem:
508 	resw 1	; in kilobytes
509 highmem:
510 	resw 1	; in kilobytes
511 idt:
512 	resq 256
513 .end:
514 	resb 512
515 stack:
516 tss:
517 	resb TSS.size