File: udelay.c

package info (click to toggle)
flashrom 0.9.2+r1141-2
  • links: PTS
  • area: main
  • in suites: squeeze
  • size: 1,536 kB
  • ctags: 1,827
  • sloc: ansic: 20,878; makefile: 322
file content (181 lines) | stat: -rw-r--r-- 5,174 bytes parent folder | download
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
/*
 * This file is part of the flashrom project.
 *
 * Copyright (C) 2000 Silicon Integrated System Corporation
 * Copyright (C) 2009,2010 Carl-Daniel Hailfinger
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#include <unistd.h>
#include <sys/time.h>
#include <stdlib.h>
#include <limits.h>
#include "flash.h"

/* loops per microsecond */
static unsigned long micro = 1;

__attribute__ ((noinline)) void myusec_delay(int usecs)
{
	unsigned long i;
	for (i = 0; i < usecs * micro; i++) {
		/* Make sure the compiler doesn't optimize the loop away. */
		asm volatile ("" : : "rm" (i) );
	}
}

static unsigned long measure_os_delay_resolution(void)
{
	unsigned long timeusec;
	struct timeval start, end;
	unsigned long counter = 0;
	
	gettimeofday(&start, 0);
	timeusec = 0;
	
	while (!timeusec && (++counter < 1000000000)) {
		gettimeofday(&end, 0);
		timeusec = 1000000 * (end.tv_sec - start.tv_sec) +
			   (end.tv_usec - start.tv_usec);
		/* Protect against time going forward too much. */
		if ((end.tv_sec > start.tv_sec) &&
		    ((end.tv_sec - start.tv_sec) >= LONG_MAX / 1000000 - 1))
			timeusec = 0;
		/* Protect against time going backwards during leap seconds. */
		if ((end.tv_sec < start.tv_sec) || (timeusec > LONG_MAX))
			timeusec = 0;
	}
	return timeusec;
}

static unsigned long measure_delay(int usecs)
{
	unsigned long timeusec;
	struct timeval start, end;
	
	gettimeofday(&start, 0);
	myusec_delay(usecs);
	gettimeofday(&end, 0);
	timeusec = 1000000 * (end.tv_sec - start.tv_sec) +
		   (end.tv_usec - start.tv_usec);
	/* Protect against time going forward too much. */
	if ((end.tv_sec > start.tv_sec) &&
	    ((end.tv_sec - start.tv_sec) >= LONG_MAX / 1000000 - 1))
		timeusec = LONG_MAX;
	/* Protect against time going backwards during leap seconds. */
	if ((end.tv_sec < start.tv_sec) || (timeusec > LONG_MAX))
		timeusec = 1;

	return timeusec;
}

void myusec_calibrate_delay(void)
{
	unsigned long count = 1000;
	unsigned long timeusec, resolution;
	int i, tries = 0;

	msg_pinfo("Calibrating delay loop... ");
	resolution = measure_os_delay_resolution();
	if (resolution) {
		msg_pdbg("OS timer resolution is %lu usecs, ", resolution);
	} else {
		msg_pinfo("OS timer resolution is unusable. ");
	}

recalibrate:
	count = 1000;
	while (1) {
		timeusec = measure_delay(count);
		if (timeusec > 1000000 / 4)
			break;
		if (count >= ULONG_MAX / 2) {
			msg_pinfo("timer loop overflow, reduced precision. ");
			break;
		}
		count *= 2;
	}
	tries ++;

	/* Avoid division by zero, but in that case the loop is shot anyway. */
	if (!timeusec)
		timeusec = 1;
	
	/* Compute rounded up number of loops per microsecond. */
	micro = (count * micro) / timeusec + 1;
	msg_pdbg("%luM loops per second, ", micro);

	/* Did we try to recalibrate less than 5 times? */
	if (tries < 5) {
		/* Recheck our timing to make sure we weren't just hitting
		 * a scheduler delay or something similar.
		 */
		for (i = 0; i < 4; i++) {
			if (resolution && (resolution < 10)) {
				timeusec = measure_delay(100);
			} else if (resolution && 
				   (resolution < ULONG_MAX / 200)) {
				timeusec = measure_delay(resolution * 10) *
					   100 / (resolution * 10);
			} else {
				/* This workaround should be active for broken
				 * OS and maybe libpayload. The criterion
				 * here is horrible or non-measurable OS timer
				 * resolution which will result in
				 * measure_delay(100)=0 whereas a longer delay
				 * (1000 ms) may be sufficient
				 * to get a nonzero time measurement.
				 */
				timeusec = measure_delay(1000000) / 10000;
			}
			if (timeusec < 90) {
				msg_pdbg("delay more than 10%% too short (got "
					 "%lu%% of expected delay), "
					 "recalculating... ", timeusec);
				goto recalibrate;
			}
		}
	} else {
		msg_perr("delay loop is unreliable, trying to continue ");
	}

	/* We're interested in the actual precision. */
	timeusec = measure_delay(10);
	msg_pdbg("10 myus = %ld us, ", timeusec);
	timeusec = measure_delay(100);
	msg_pdbg("100 myus = %ld us, ", timeusec);
	timeusec = measure_delay(1000);
	msg_pdbg("1000 myus = %ld us, ", timeusec);
	timeusec = measure_delay(10000);
	msg_pdbg("10000 myus = %ld us, ", timeusec);
	timeusec = measure_delay(resolution * 4);
	msg_pdbg("%ld myus = %ld us, ", resolution * 4, timeusec);

	msg_pinfo("OK.\n");
}

void internal_delay(int usecs)
{
	/* If the delay is >1 s, use usleep because timing does not need to
	 * be so precise.
	 */
	if (usecs > 1000000) {
		usleep(usecs);
	} else {
		myusec_delay(usecs);
	}
}