1 Watchdog Timer Interfaces For The Linux Operating System
2
3 Alan Cox <alan@lxorguk.ukuu.org.uk>
4
5 Custom Linux Driver And Program Development
6
7
8 The following watchdog drivers are currently implemented:
9
10 ICS WDT501-P
11 ICS WDT501-P (no fan tachometer)
12 ICS WDT500-P
13 Software Only
14 Berkshire Products PC Watchdog Revision A & C (by Ken Hollis)
15
16
17 All six interfaces provide /dev/watchdog, which when open must be written
18 to within a timeout or the machine will reboot. Each write delays the reboot
19 time another timeout. In the case of the software watchdog the ability to
20 reboot will depend on the state of the machines and interrupts. The hardware
21 boards physically pull the machine down off their own onboard timers and
22 will reboot from almost anything.
23
24 A second temperature monitoring interface is available on the WDT501P cards
25 and some Berkshire cards. This provides /dev/temperature. This is the machine
26 internal temperature in degrees Fahrenheit. Each read returns a single byte
27 giving the temperature.
28
29 The third interface logs kernel messages on additional alert events.
30
31 Both software and hardware watchdog drivers are available in the standard
32 kernel. If you are using the software watchdog, you probably also want
33 to use "panic=60" as a boot argument as well.
34
35 The wdt card cannot be safely probed for. Instead you need to pass
36 wdt=ioaddr,irq as a boot parameter - eg "wdt=0x240,11".
37
38 The i810 TCO watchdog modules can be configured with the "i810_margin"
39 commandline argument which specifies the counter initial value. The counter
40 is decremented every 0.6 seconds and default to 50 (30 seconds). Values can
41 range between 3 and 63.
42
43 The i810 TCO watchdog driver also implements the WDIOC_GETSTATUS and
44 WDIOC_GETBOOTSTATUS ioctl()s. WDIOC_GETSTATUS returns the actual counter value
45 and WDIOC_GETBOOTSTATUS returns the value of TCO2 Status Register (see Intel's
46 documentation for the 82801AA and 82801AB datasheet).
47
48 Features
49 --------
50 WDT501P WDT500P Software Berkshire i810 TCO
51 Reboot Timer X X X X X
52 External Reboot X X o o o
53 I/O Port Monitor o o o X o
54 Temperature X o o X o
55 Fan Speed X o o o o
56 Power Under X o o o o
57 Power Over X o o o o
58 Overheat X o o o o
59
60 The external event interfaces on the WDT boards are not currently supported.
61 Minor numbers are however allocated for it.
62
63
64 Example Watchdog Driver
65 -----------------------
66
67 #include <stdio.h>
68 #include <unistd.h>
69 #include <fcntl.h>
70
71 int main(int argc, const char *argv[])
72 {
73 int fd=open("/dev/watchdog",O_WRONLY);
74 if(fd==-1)
75 {
76 perror("watchdog");
77 exit(1);
78 }
79 while(1)
80 {
81 write(fd,"\0",1);
82 fsync(fd);
83 sleep(10);
84 }
85 }
86
87
88 Contact Information
89
90 People keep asking about the WDT watchdog timer hardware: The phone contacts
91 for Industrial Computer Source are:
92
93 Industrial Computer Source
94 http://www.indcompsrc.com
95 ICS Advent, San Diego
96 6260 Sequence Dr.
97 San Diego, CA 92121-4371
98 Phone (858) 677-0877
99 FAX: (858) 677-0895
100 >
101 ICS Advent Europe, UK
102 Oving Road
103 Chichester,
104 West Sussex,
105 PO19 4ET, UK
106 Phone: 00.44.1243.533900
107
108
109 and please mention Linux when enquiring.
110
111 For full information about the PCWD cards see the pcwd-watchdog.txt document.
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