aboutsummaryrefslogtreecommitdiff
path: root/arch/frv/kernel/head.S
blob: e9a8cc63ac9413a0233f6f55ec0d91693ee3cf57 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
/* head.S: kernel entry point for FR-V kernel
 *
 * Copyright (C) 2003, 2004 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/init.h>
#include <linux/threads.h>
#include <linux/linkage.h>
#include <asm/thread_info.h>
#include <asm/ptrace.h>
#include <asm/page.h>
#include <asm/spr-regs.h>
#include <asm/mb86943a.h>
#include <asm/cache.h>
#include "head.inc"

###############################################################################
#
# void _boot(unsigned long magic, char *command_line) __attribute__((noreturn))
#
# - if magic is 0xdead1eaf, then command_line is assumed to point to the kernel
#   command line string
#
###############################################################################
	__HEAD
	.balign		4

	.globl		_boot, __head_reference
        .type		_boot,@function
_boot:
__head_reference:
	sethi.p		%hi(LED_ADDR),gr30
	setlo		%lo(LED_ADDR),gr30

	LEDS		0x0000

	# calculate reference address for PC-relative stuff
	call		0f
0:	movsg		lr,gr26
	addi		gr26,#__head_reference-0b,gr26

	# invalidate and disable both of the caches and turn off the memory access checking
	dcef		@(gr0,gr0),1
	bar

	sethi.p		%hi(~(HSR0_ICE|HSR0_DCE|HSR0_CBM|HSR0_EIMMU|HSR0_EDMMU)),gr4
	setlo		%lo(~(HSR0_ICE|HSR0_DCE|HSR0_CBM|HSR0_EIMMU|HSR0_EDMMU)),gr4
	movsg		hsr0,gr5
	and		gr4,gr5,gr5
	movgs		gr5,hsr0
	movsg		hsr0,gr5

	LEDS		0x0001

	icei		@(gr0,gr0),1
	dcei		@(gr0,gr0),1
	bar

	# turn the instruction cache back on
	sethi.p		%hi(HSR0_ICE),gr4
	setlo		%lo(HSR0_ICE),gr4
	movsg		hsr0,gr5
	or		gr4,gr5,gr5
	movgs		gr5,hsr0
	movsg		hsr0,gr5

	bar

	LEDS		0x0002

	# retrieve the parameters (including command line) before we overwrite them
	sethi.p		%hi(0xdead1eaf),gr7
	setlo		%lo(0xdead1eaf),gr7
	subcc		gr7,gr8,gr0,icc0
	bne		icc0,#0,__head_no_parameters

	sethi.p		%hi(redboot_command_line-1),gr6
	setlo		%lo(redboot_command_line-1),gr6
	sethi.p		%hi(__head_reference),gr4
	setlo		%lo(__head_reference),gr4
	sub		gr6,gr4,gr6
	add.p		gr6,gr26,gr6
	subi		gr9,#1,gr9
	setlos.p	#511,gr4
	setlos		#1,gr5

__head_copy_cmdline:
	ldubu.p		@(gr9,gr5),gr16
	subicc		gr4,#1,gr4,icc0
	stbu.p		gr16,@(gr6,gr5)
	subicc		gr16,#0,gr0,icc1
	bls		icc0,#0,__head_end_cmdline
	bne		icc1,#1,__head_copy_cmdline
__head_end_cmdline:
	stbu		gr0,@(gr6,gr5)
__head_no_parameters:

###############################################################################
#
# we need to relocate the SDRAM to 0x00000000 (linux) or 0xC0000000 (uClinux)
# - note that we're going to have to run entirely out of the icache whilst
#   fiddling with the SDRAM controller registers
#
###############################################################################
#ifdef CONFIG_MMU
	call		__head_fr451_describe_sdram

#else
	movsg		psr,gr5
	srli		gr5,#28,gr5
	subicc		gr5,#3,gr0,icc0
	beq		icc0,#0,__head_fr551_sdram

	call		__head_fr401_describe_sdram
	bra		__head_do_sdram

__head_fr551_sdram:
	call		__head_fr555_describe_sdram
	LEDS		0x000d

__head_do_sdram:
#endif

	# preload the registers with invalid values in case any DBR/DARS are marked not present
	sethi.p		%hi(0xfe000000),gr17		; unused SDRAM DBR value
	setlo		%lo(0xfe000000),gr17
	or.p		gr17,gr0,gr20
	or		gr17,gr0,gr21
	or.p		gr17,gr0,gr22
	or		gr17,gr0,gr23

	# consult the SDRAM controller CS address registers
	cld		@(gr14,gr0 ),gr20,	cc0,#1	; DBR0 / DARS0
	cld		@(gr14,gr11),gr21,	cc1,#1	; DBR1 / DARS1
	cld		@(gr14,gr12),gr22,	cc2,#1	; DBR2 / DARS2
	cld.p		@(gr14,gr13),gr23,	cc3,#1	; DBR3 / DARS3

	sll		gr20,gr15,gr20			; shift values up for FR551
	sll		gr21,gr15,gr21
	sll		gr22,gr15,gr22
	sll		gr23,gr15,gr23

	LEDS		0x0003

	# assume the lowest valid CS line to be the SDRAM base and get its address
	subcc		gr20,gr17,gr0,icc0
	subcc.p		gr21,gr17,gr0,icc1
	subcc		gr22,gr17,gr0,icc2
	subcc.p		gr23,gr17,gr0,icc3
	ckne		icc0,cc4			; T if DBR0 != 0xfe000000
	ckne		icc1,cc5
	ckne		icc2,cc6
	ckne		icc3,cc7
	cor		gr23,gr0,gr24,		cc7,#1	; GR24 = SDRAM base
	cor		gr22,gr0,gr24,		cc6,#1
	cor		gr21,gr0,gr24,		cc5,#1
	cor		gr20,gr0,gr24,		cc4,#1

	# calculate the displacement required to get the SDRAM into the right place in memory
	sethi.p		%hi(__sdram_base),gr16
	setlo		%lo(__sdram_base),gr16
	sub		gr16,gr24,gr16			; delta = __sdram_base - DBRx

	# calculate the new values to go in the controller regs
	cadd.p		gr20,gr16,gr20,		cc4,#1	; DCS#0 (new) = DCS#0 (old) + delta
	cadd		gr21,gr16,gr21,		cc5,#1
	cadd.p		gr22,gr16,gr22,		cc6,#1
	cadd		gr23,gr16,gr23,		cc7,#1

	srl		gr20,gr15,gr20			; shift values down for FR551
	srl		gr21,gr15,gr21
	srl		gr22,gr15,gr22
	srl		gr23,gr15,gr23

	# work out the address at which the reg updater resides and lock it into icache
	# also work out the address the updater will jump to when finished
	sethi.p		%hi(__head_move_sdram-__head_reference),gr18
	setlo		%lo(__head_move_sdram-__head_reference),gr18
	sethi.p		%hi(__head_sdram_moved-__head_reference),gr19
	setlo		%lo(__head_sdram_moved-__head_reference),gr19
	add.p		gr18,gr26,gr18
	add		gr19,gr26,gr19
	add.p		gr19,gr16,gr19			; moved = addr + (__sdram_base - DBRx)
	add		gr18,gr5,gr4			; two cachelines probably required

	icpl		gr18,gr0,#1			; load and lock the cachelines
	icpl		gr4,gr0,#1
	LEDS		0x0004
	membar
	bar
	jmpl		@(gr18,gr0)

	.balign		L1_CACHE_BYTES
__head_move_sdram:
	cst		gr20,@(gr14,gr0 ),	cc4,#1
	cst		gr21,@(gr14,gr11),	cc5,#1
	cst		gr22,@(gr14,gr12),	cc6,#1
	cst		gr23,@(gr14,gr13),	cc7,#1
	cld		@(gr14,gr0 ),gr20,	cc4,#1
	cld		@(gr14,gr11),gr21,	cc5,#1
	cld		@(gr14,gr12),gr22,	cc4,#1
	cld		@(gr14,gr13),gr23,	cc7,#1
	bar
	membar
	jmpl		@(gr19,gr0)

	.balign		L1_CACHE_BYTES
__head_sdram_moved:
	icul		gr18
	add		gr18,gr5,gr4
	icul		gr4
	icei		@(gr0,gr0),1
	dcei		@(gr0,gr0),1

	LEDS		0x0005

	# recalculate reference address
	call		0f
0:	movsg		lr,gr26
	addi		gr26,#__head_reference-0b,gr26


###############################################################################
#
# move the kernel image down to the bottom of the SDRAM
#
###############################################################################
	sethi.p		%hi(__kernel_image_size_no_bss+15),gr4
	setlo		%lo(__kernel_image_size_no_bss+15),gr4
	srli.p		gr4,#4,gr4			; count
	or		gr26,gr26,gr16			; source

	sethi.p		%hi(__sdram_base),gr17		; destination
	setlo		%lo(__sdram_base),gr17

	setlos		#8,gr5
	sub.p		gr16,gr5,gr16			; adjust src for LDDU
	sub		gr17,gr5,gr17			; adjust dst for LDDU

	sethi.p		%hi(__head_move_kernel-__head_reference),gr18
	setlo		%lo(__head_move_kernel-__head_reference),gr18
	sethi.p		%hi(__head_kernel_moved-__head_reference+__sdram_base),gr19
	setlo		%lo(__head_kernel_moved-__head_reference+__sdram_base),gr19
	add		gr18,gr26,gr18
	icpl		gr18,gr0,#1
	jmpl		@(gr18,gr0)

	.balign		32
__head_move_kernel:
	lddu		@(gr16,gr5),gr10
	lddu		@(gr16,gr5),gr12
	stdu.p		gr10,@(gr17,gr5)
	subicc		gr4,#1,gr4,icc0
	stdu.p		gr12,@(gr17,gr5)
	bhi		icc0,#0,__head_move_kernel
	jmpl		@(gr19,gr0)

	.balign		32
__head_kernel_moved:
	icul		gr18
	icei		@(gr0,gr0),1
	dcei		@(gr0,gr0),1

	LEDS		0x0006

	# recalculate reference address
	call		0f
0:	movsg		lr,gr26
	addi		gr26,#__head_reference-0b,gr26


###############################################################################
#
# rearrange the iomem map and set the protection registers
#
###############################################################################

#ifdef CONFIG_MMU
	LEDS		0x3301
	call		__head_fr451_set_busctl
	LEDS		0x3303
	call		__head_fr451_survey_sdram
	LEDS		0x3305
	call		__head_fr451_set_protection

#else
	movsg		psr,gr5
	srli		gr5,#PSR_IMPLE_SHIFT,gr5
	subicc		gr5,#PSR_IMPLE_FR551,gr0,icc0
	beq		icc0,#0,__head_fr555_memmap
	subicc		gr5,#PSR_IMPLE_FR451,gr0,icc0
	beq		icc0,#0,__head_fr451_memmap

	LEDS		0x3101
	call		__head_fr401_set_busctl
	LEDS		0x3103
	call		__head_fr401_survey_sdram
	LEDS		0x3105
	call		__head_fr401_set_protection
	bra		__head_done_memmap

__head_fr451_memmap:
	LEDS		0x3301
	call		__head_fr401_set_busctl
	LEDS		0x3303
	call		__head_fr401_survey_sdram
	LEDS		0x3305
	call		__head_fr451_set_protection
	bra		__head_done_memmap

__head_fr555_memmap:
	LEDS		0x3501
	call		__head_fr555_set_busctl
	LEDS		0x3503
	call		__head_fr555_survey_sdram
	LEDS		0x3505
	call		__head_fr555_set_protection

__head_done_memmap:
#endif
	LEDS		0x0007

###############################################################################
#
# turn the data cache and MMU on
# - for the FR451 this'll mean that the window through which the kernel is
#   viewed will change
#
###############################################################################

#ifdef CONFIG_MMU
#define MMUMODE		HSR0_EIMMU|HSR0_EDMMU|HSR0_EXMMU|HSR0_EDAT|HSR0_XEDAT
#else
#define MMUMODE		HSR0_EIMMU|HSR0_EDMMU
#endif

	movsg		hsr0,gr5

	sethi.p		%hi(MMUMODE),gr4
	setlo		%lo(MMUMODE),gr4
	or		gr4,gr5,gr5

#if defined(CONFIG_FRV_DEFL_CACHE_WTHRU)
	sethi.p		%hi(HSR0_DCE|HSR0_CBM_WRITE_THRU),gr4
	setlo		%lo(HSR0_DCE|HSR0_CBM_WRITE_THRU),gr4
#elif defined(CONFIG_FRV_DEFL_CACHE_WBACK)
	sethi.p		%hi(HSR0_DCE|HSR0_CBM_COPY_BACK),gr4
	setlo		%lo(HSR0_DCE|HSR0_CBM_COPY_BACK),gr4
#elif defined(CONFIG_FRV_DEFL_CACHE_WBEHIND)
	sethi.p		%hi(HSR0_DCE|HSR0_CBM_COPY_BACK),gr4
	setlo		%lo(HSR0_DCE|HSR0_CBM_COPY_BACK),gr4

	movsg		psr,gr6
	srli		gr6,#24,gr6
	cmpi		gr6,#0x50,icc0		// FR451
	beq		icc0,#0,0f
	cmpi		gr6,#0x40,icc0		// FR405
	bne		icc0,#0,1f
0:
	# turn off write-allocate
	sethi.p		%hi(HSR0_NWA),gr6
	setlo		%lo(HSR0_NWA),gr6
	or		gr4,gr6,gr4
1:

#else
#error No default cache configuration set
#endif

	or		gr4,gr5,gr5
	movgs		gr5,hsr0
	bar

	LEDS		0x0008

	sethi.p		%hi(__head_mmu_enabled),gr19
	setlo		%lo(__head_mmu_enabled),gr19
	jmpl		@(gr19,gr0)

__head_mmu_enabled:
	icei		@(gr0,gr0),#1
	dcei		@(gr0,gr0),#1

	LEDS		0x0009

#ifdef CONFIG_MMU
	call		__head_fr451_finalise_protection
#endif

	LEDS		0x000a

###############################################################################
#
# set up the runtime environment
#
###############################################################################

	# clear the BSS area
	sethi.p		%hi(__bss_start),gr4
	setlo		%lo(__bss_start),gr4
	sethi.p		%hi(_end),gr5
	setlo		%lo(_end),gr5
	or.p		gr0,gr0,gr18
	or		gr0,gr0,gr19

0:
	stdi		gr18,@(gr4,#0)
	stdi		gr18,@(gr4,#8)
	stdi		gr18,@(gr4,#16)
	stdi.p		gr18,@(gr4,#24)
	addi		gr4,#24,gr4
	subcc		gr5,gr4,gr0,icc0
	bhi		icc0,#2,0b

	LEDS		0x000b

	# save the SDRAM details
	sethi.p		%hi(__sdram_old_base),gr4
	setlo		%lo(__sdram_old_base),gr4
	st		gr24,@(gr4,gr0)

	sethi.p		%hi(__sdram_base),gr5
	setlo		%lo(__sdram_base),gr5
	sethi.p		%hi(memory_start),gr4
	setlo		%lo(memory_start),gr4
	st		gr5,@(gr4,gr0)

	add		gr25,gr5,gr25
	sethi.p		%hi(memory_end),gr4
	setlo		%lo(memory_end),gr4
	st		gr25,@(gr4,gr0)

	# point the TBR at the kernel trap table
	sethi.p		%hi(__entry_kerneltrap_table),gr4
	setlo		%lo(__entry_kerneltrap_table),gr4
	movgs		gr4,tbr

	# set up the exception frame for init
	sethi.p		%hi(__kernel_frame0_ptr),gr28
	setlo		%lo(__kernel_frame0_ptr),gr28
	sethi.p		%hi(_gp),gr16
	setlo		%lo(_gp),gr16
	sethi.p		%hi(__entry_usertrap_table),gr4
	setlo		%lo(__entry_usertrap_table),gr4

	lddi		@(gr28,#0),gr28		; load __frame & current
	ldi.p		@(gr29,#4),gr15		; set current_thread

	or		gr0,gr0,fp
	or		gr28,gr0,sp

	sti.p		gr4,@(gr28,REG_TBR)
	setlos		#ISR_EDE|ISR_DTT_DIVBYZERO|ISR_EMAM_EXCEPTION,gr5
	movgs		gr5,isr

	# turn on and off various CPU services
	movsg		psr,gr22
	sethi.p		%hi(#PSR_EM|PSR_EF|PSR_CM|PSR_NEM),gr4
	setlo		%lo(#PSR_EM|PSR_EF|PSR_CM|PSR_NEM),gr4
	or		gr22,gr4,gr22
	movgs		gr22,psr

	andi		gr22,#~(PSR_PIL|PSR_PS|PSR_S),gr22
	ori		gr22,#PSR_ET,gr22
	sti		gr22,@(gr28,REG_PSR)


###############################################################################
#
# set up the registers and jump into the kernel
#
###############################################################################

	LEDS		0x000c

	# initialise the processor and the peripherals
	#call		SYMBOL_NAME(processor_init)
	#call		SYMBOL_NAME(unit_init)
	#LEDS		0x0aff

	sethi.p		#0xe5e5,gr3
	setlo		#0xe5e5,gr3
	or.p		gr3,gr0,gr4
	or		gr3,gr0,gr5
	or.p		gr3,gr0,gr6
	or		gr3,gr0,gr7
	or.p		gr3,gr0,gr8
	or		gr3,gr0,gr9
	or.p		gr3,gr0,gr10
	or		gr3,gr0,gr11
	or.p		gr3,gr0,gr12
	or		gr3,gr0,gr13
	or.p		gr3,gr0,gr14
	or		gr3,gr0,gr17
	or.p		gr3,gr0,gr18
	or		gr3,gr0,gr19
	or.p		gr3,gr0,gr20
	or		gr3,gr0,gr21
	or.p		gr3,gr0,gr23
	or		gr3,gr0,gr24
	or.p		gr3,gr0,gr25
	or		gr3,gr0,gr26
	or.p		gr3,gr0,gr27
#	or		gr3,gr0,gr30
	or		gr3,gr0,gr31
	movgs		gr0,lr
	movgs		gr0,lcr
	movgs		gr0,ccr
	movgs		gr0,cccr

	# initialise the virtual interrupt handling
	subcc		gr0,gr0,gr0,icc2		/* set Z, clear C */

#ifdef CONFIG_MMU
	movgs		gr3,scr2
	movgs		gr3,scr3
#endif

	LEDS		0x0fff

	# invoke the debugging stub if present
	# - arch/frv/kernel/debug-stub.c will shift control directly to init/main.c
	#   (it will not return here)
	break
	.globl		__debug_stub_init_break
__debug_stub_init_break:

	# however, if you need to use an ICE, and don't care about using any userspace
	# debugging tools (such as the ptrace syscall), you can just step over the break
	# above and get to the kernel this way
	# look at arch/frv/kernel/debug-stub.c: debug_stub_init() to see what you've missed
	call		start_kernel

	.globl		__head_end
__head_end:
	.size		_boot, .-_boot

	# provide a point for GDB to place a break
	.section	.text..start,"ax"
	.globl		_start
	.balign		4
_start:
	call		_boot

	.previous
###############################################################################
#
# split a tile off of the region defined by GR8-GR9
#
#	ENTRY:			EXIT:
# GR4	-			IAMPR value representing tile
# GR5	-			DAMPR value representing tile
# GR6	-			IAMLR value representing tile
# GR7	-			DAMLR value representing tile
# GR8	region base pointer	[saved]
# GR9	region top pointer	updated to exclude new tile
# GR11	xAMLR mask		[saved]
# GR25	SDRAM size		[saved]
# GR30	LED address		[saved]
#
# - GR8 and GR9 should be rounded up/down to the nearest megabyte before calling
#
###############################################################################
	.globl		__head_split_region
	.type		__head_split_region,@function
__head_split_region:
	subcc.p		gr9,gr8,gr4,icc0
	setlos		#31,gr5
	scan.p		gr4,gr0,gr6
	beq		icc0,#0,__head_region_empty
	sub.p		gr5,gr6,gr6			; bit number of highest set bit (1MB=>20)
	setlos		#1,gr4
	sll.p		gr4,gr6,gr4			; size of region (1 << bitno)
	subi		gr6,#17,gr6			; 1MB => 0x03
	slli.p		gr6,#4,gr6			; 1MB => 0x30
	sub		gr9,gr4,gr9			; move uncovered top down

	or		gr9,gr6,gr4
	ori		gr4,#xAMPRx_S_USER|xAMPRx_C_CACHED|xAMPRx_V,gr4
	or.p		gr4,gr0,gr5

	and		gr4,gr11,gr6
	and.p		gr5,gr11,gr7
	bralr

__head_region_empty:
	or.p		gr0,gr0,gr4
	or		gr0,gr0,gr5
	or.p		gr0,gr0,gr6
	or		gr0,gr0,gr7
	bralr
	.size		__head_split_region, .-__head_split_region

###############################################################################
#
# write the 32-bit hex number in GR8 to ttyS0
#
###############################################################################
#if 0
	.globl		__head_write_to_ttyS0
	.type		__head_write_to_ttyS0,@function
__head_write_to_ttyS0:
	sethi.p		%hi(0xfeff9c00),gr31
	setlo		%lo(0xfeff9c00),gr31
	setlos		#8,gr20

0:	ldubi		@(gr31,#5*8),gr21
	andi		gr21,#0x60,gr21
	subicc		gr21,#0x60,gr21,icc0
	bne		icc0,#0,0b

1:	srli		gr8,#28,gr21
	slli		gr8,#4,gr8

	addi		gr21,#'0',gr21
	subicc		gr21,#'9',gr0,icc0
	bls		icc0,#2,2f
	addi		gr21,#'A'-'0'-10,gr21
2:
	stbi		gr21,@(gr31,#0*8)
	subicc		gr20,#1,gr20,icc0
	bhi		icc0,#2,1b

	setlos		#'\r',gr21
	stbi		gr21,@(gr31,#0*8)

	setlos		#'\n',gr21
	stbi		gr21,@(gr31,#0*8)

3:	ldubi		@(gr31,#5*8),gr21
	andi		gr21,#0x60,gr21
	subicc		gr21,#0x60,gr21,icc0
	bne		icc0,#0,3b
	bralr

	.size		__head_write_to_ttyS0, .-__head_write_to_ttyS0
#endif