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
|
<!--startcut ==============================================-->
<!-- *** BEGIN HTML header *** -->
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML><HEAD>
<title>Programming the SA1110 Watchdog timer on the Simputer LG #88</title>
</HEAD>
<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#0000AF"
ALINK="#FF0000">
<!-- *** END HTML header *** -->
<!-- *** BEGIN navbar *** -->
<IMG ALT="" SRC="../gx/navbar/left.jpg" WIDTH="14" HEIGHT="45" BORDER="0" ALIGN="bottom"><A HREF="piszcz.html"><IMG ALT="[ Prev ]" SRC="../gx/navbar/prev.jpg" WIDTH="16" HEIGHT="45" BORDER="0" ALIGN="bottom"></A><A HREF="index.html"><IMG ALT="[ Table of Contents ]" SRC="../gx/navbar/toc.jpg" WIDTH="220" HEIGHT="45" BORDER="0" ALIGN="bottom" ></A><A HREF="../index.html"><IMG ALT="[ Front Page ]" SRC="../gx/navbar/frontpage.jpg" WIDTH="137" HEIGHT="45" BORDER="0" ALIGN="bottom"></A><A HREF="http://www.linuxgazette.com/cgi-bin/talkback/all.py?site=LG&article=http://www.linuxgazette.com/issue88/pramode.html"><IMG ALT="[ Talkback ]" SRC="../gx/navbar/talkback.jpg" WIDTH="121" HEIGHT="45" BORDER="0" ALIGN="bottom" ></A><A HREF="../lg_faq.html"><IMG ALT="[ FAQ ]" SRC="./../gx/navbar/faq.jpg"WIDTH="62" HEIGHT="45" BORDER="0" ALIGN="bottom"></A><A HREF="puryear.html"><IMG ALT="[ Next ]" SRC="../gx/navbar/next.jpg" WIDTH="15" HEIGHT="45" BORDER="0" ALIGN="bottom" ></A><IMG ALT="" SRC="../gx/navbar/right.jpg" WIDTH="15" HEIGHT="45" ALIGN="bottom">
<!-- *** END navbar *** -->
<!--endcut ============================================================-->
<TABLE BORDER><TR><TD WIDTH="200">
<A HREF="http://www.linuxgazette.com/">
<IMG ALT="LINUX GAZETTE" SRC="../gx/2002/lglogo_200x41.png"
WIDTH="200" HEIGHT="41" border="0"></A>
<BR CLEAR="all">
<SMALL>...<I>making Linux just a little more fun!</I></SMALL>
</TD><TD WIDTH="380">
<CENTER>
<BIG><BIG><STRONG><FONT COLOR="maroon">Programming the SA1110 Watchdog timer on the Simputer </FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/pramode.html">Pramode C.E</A></STRONG>
</CENTER>
</TD></TR>
</TABLE>
<P>
<!-- END header -->
<p>
In last month's article (Fun with Simputer and Embedded Linux),
I had described the process of developing programs for the
Simputer, a StrongArm based handheld device. The Simputer
can be used as a platform for learning microprocessor and
embedded systems programming. This article describes my
attempts at programming the watchdog timer unit attached
to the SA1110 CPU which powers the Simputer. The experiments
should work on any Linux based handheld which uses the same
CPU.
<h2> The Watchdog timer </h2>
<p>
Due to obscure bugs, your computer system is going to lock
up once in a while - the only way out would be to reset
the unit. But what if you are not there to press the switch?
You need to have some form of `automatic reset'.
The watchdog timer presents such a solution.
<p>
Imagine that your microprocessor contains two registers -
one which gets incremented every time there is a low to
high (or high to low) transition of a clock signal (generated
internal to the microprocessor or coming from some external
source) and another one which simply stores a number. Let's
assume that the first register starts out at zero and is
incremented at a rate of 4,000,000 per second. Lets assume
that the second register contains the number 4,000,000,0.
The microprocessor hardware compares these two registers
every time the first register is incremented and issues
a reset signal (which has the result of rebooting the system)
when the value of these registers match. Now, if we do not
modify the value in the second register, our system is sure
to reboot in 10 seconds - the time required for the values
in both registers to become equal.
<p>
The trick is this - we do not allow the values in these registers
to become equal. We run a program (either as part of the
OS kernel or in user space) which keeps on moving the value
in the second register forward before the values of both
become equal. If this program does not execute (because
of a system freeze), then the unit would be automatically
rebooted the moment the value of the two registers match.
Hopefully, the system will start functioning normally after
the reboot.
<h2> Resetting the SA1110 </h2>
<p>
The Intel StrongArm manual specifies that a software reset
is invoked when the Software Reset (SWR) bit of a register
called RSRR (Reset Controller Software Register) is set.
The SWR bit is bit D0 of this 32 bit register. My first
experiment was to try resetting the Simputer by setting
this bit. I was able to do so by compiling a simple module
whose `init_module' contained only one line:
<p>
RSRR = RSRR | 0x1
</p>
<h2> The Operating System Timer </h2>
<p>
The StrongArm CPU contains a 32 bit timer that is clocked
by a 3.6864MHz oscillator. The timer contains an OSCR (operating
system count register) which is an up counter and four 32
bit match registers (OSMR0 to OSMR3). Of special interest
to us is the OSMR3.
<p>
If bit D0 of the OS Timer Watchdog Match Enable Register
(OWER) is set, a reset is issued by the hardware when the
value in OSMR3 becomes equal to the value in OSCR. It seems
that bit D3 of the OS Timer Interrupt Enable Register (OIER)
should also be set for the reset to occur.
<p>
Using these ideas, it is easy to write a simple character
driver with only one method - `write'. A write will delay
the reset by a period defined by the constant `TIMEOUT'.
<p>
[<A HREF="misc/pramode/watchdog.c.txt">Text version of this listing</A>]
<p>
<pre>
/*
* A watchdog timer.
*/
#include <linux/module.h>
#include <linux/ioport.h>
#include <linux/sched.h>
#include <asm-arm/irq.h>
#include <asm/io.h>
#define WME 1
#define OSCLK 3686400 /* The OS counter gets incremented
* at this rate
* every second
*/
#define TIMEOUT 20 /* 20 seconds timeout */
static int major;
static char *name = "watchdog";
void
enable_watchdog(void)
{
OWER = OWER | WME;
}
void
enable_interrupt(void)
{
OIER = OIER | 0x8;
}
ssize_t
watchdog_write(struct file *filp, const char *buf, size_t
count, loff_t *offp)
{
OSMR3 = OSCR + TIMEOUT*OSCLK;
printk("OSMR3 updated...\n");
return count;
}
static struct file_operations fops = {write:watchdog_write};
int
init_module(void)
{
major = register_chrdev(0, name, &fops);
if(major < 0) {
printk("error in init_module...\n");
return major;
}
printk("Major = %d\n", major);
OSMR3 = OSCR + TIMEOUT*OSCLK;
enable_watchdog();
enable_interrupt();
return 0;
}
void
cleanup_module()
{
unregister_chrdev(major, name);
}
</pre>
</p>
<p>
It would be nice to add an `ioctl' method which can be used
at least for getting and setting the timeout period.
<p>
Once the module is loaded, we can think of running the following
program in the background (of course, we have to first create
a device file called `watchdog' with the major number which
`init_module' had printed). As long as this program keeps
running, the system will not reboot.
<p>
[<A HREF="misc/pramode/shutter_upper.c.txt">Text version of this listing</A>]
<p>
<pre>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#define TIMEOUT 20
main()
{
int fd, buf;
fd = open("watchdog", O_WRONLY);
if(fd < 0) {
perror("Error in open");
exit(1);
}
while(1) {
if(write(fd, &buf, sizeof(buf)) < 0) {
perror("Error in write, System may reboot any moment...\n");
exit(1);
}
sleep(TIMEOUT/2);
}
}
</pre>
</p>
<h2> Conclusion </h2>
<p>
If you are not bored to death reading this, you may
be interested in knowing more about Linux on handheld
devices (and in general, embedded applications). So,
till next time, Bye!
<!-- *** BEGIN author bio *** -->
<P>
<P>
<!-- *** BEGIN bio *** -->
<P>
<img ALIGN="LEFT" ALT="[BIO]" SRC="../gx/2002/note.png">
<em>
I am an instructor working for IC Software in Kerala, India. I would have loved
becoming an organic chemist, but I do the second best thing possible, which is
play with Linux and teach programming!
</em>
<br CLEAR="all">
<!-- *** END bio *** -->
<!-- *** END author bio *** -->
<!-- *** BEGIN copyright *** -->
<hr>
<CENTER><SMALL><STRONG>
Copyright © 2003, Pramode C.E.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 88 of <i>Linux Gazette</i>, March 2003
</STRONG></SMALL></CENTER>
<!-- *** END copyright *** -->
<HR>
<!--startcut ==========================================================-->
<CENTER>
<!-- *** BEGIN navbar *** -->
<IMG ALT="" SRC="../gx/navbar/left.jpg" WIDTH="14" HEIGHT="45" BORDER="0" ALIGN="bottom"><A HREF="piszcz.html"><IMG ALT="[ Prev ]" SRC="../gx/navbar/prev.jpg" WIDTH="16" HEIGHT="45" BORDER="0" ALIGN="bottom"></A><A HREF="index.html"><IMG ALT="[ Table of Contents ]" SRC="../gx/navbar/toc.jpg" WIDTH="220" HEIGHT="45" BORDER="0" ALIGN="bottom" ></A><A HREF="../index.html"><IMG ALT="[ Front Page ]" SRC="../gx/navbar/frontpage.jpg" WIDTH="137" HEIGHT="45" BORDER="0" ALIGN="bottom"></A><A HREF="http://www.linuxgazette.com/cgi-bin/talkback/all.py?site=LG&article=http://www.linuxgazette.com/issue88/pramode.html"><IMG ALT="[ Talkback ]" SRC="../gx/navbar/talkback.jpg" WIDTH="121" HEIGHT="45" BORDER="0" ALIGN="bottom" ></A><A HREF="../lg_faq.html"><IMG ALT="[ FAQ ]" SRC="./../gx/navbar/faq.jpg"WIDTH="62" HEIGHT="45" BORDER="0" ALIGN="bottom"></A><A HREF="puryear.html"><IMG ALT="[ Next ]" SRC="../gx/navbar/next.jpg" WIDTH="15" HEIGHT="45" BORDER="0" ALIGN="bottom" ></A><IMG ALT="" SRC="../gx/navbar/right.jpg" WIDTH="15" HEIGHT="45" ALIGN="bottom">
<!-- *** END navbar *** -->
</CENTER>
</BODY></HTML>
<!--endcut ============================================================-->
|
