1 The Linux Watchdog driver API.
3 Copyright 2002 Christer Weingel <wingel@nano-system.com>
5 Some parts of this document are copied verbatim from the sbc60xxwdt
6 driver which is (c) Copyright 2000 Jakob Oestergaard <jakob@ostenfeld.dk>
8 This document describes the state of the Linux 2.4.18 kernel.
12 A Watchdog Timer (WDT) is a hardware circuit that can reset the
13 computer system in case of a software fault. You probably knew that
16 Usually a userspace daemon will notify the kernel watchdog driver via the
17 /dev/watchdog special device file that userspace is still alive, at
18 regular intervals. When such a notification occurs, the driver will
19 usually tell the hardware watchdog that everything is in order, and
20 that the watchdog should wait for yet another little while to reset
21 the system. If userspace fails (RAM error, kernel bug, whatever), the
22 notifications cease to occur, and the hardware watchdog will reset the
23 system (causing a reboot) after the timeout occurs.
25 The Linux watchdog API is a rather AD hoc construction and different
26 drivers implement different, and sometimes incompatible, parts of it.
27 This file is an attempt to document the existing usage and allow
28 future driver writers to use it as a reference.
32 All drivers support the basic mode of operation, where the watchdog
33 activates as soon as /dev/watchdog is opened and will reboot unless
34 the watchdog is pinged within a certain time, this time is called the
35 timeout or margin. The simplest way to ping the watchdog is to write
36 some data to the device. So a very simple watchdog daemon would look
42 int main(int argc, const char *argv[]) {
43 int fd=open("/dev/watchdog",O_WRONLY);
54 A more advanced driver could for example check that a HTTP server is
55 still responding before doing the write call to ping the watchdog.
57 When the device is closed, the watchdog is disabled. This is not
58 always such a good idea, since if there is a bug in the watchdog
59 daemon and it crashes the system will not reboot. Because of this,
60 some of the drivers support the configuration option "Disable watchdog
61 shutdown on close", CONFIG_WATCHDOG_NOWAYOUT. If it is set to Y when
62 compiling the kernel, there is no way of disabling the watchdog once
63 it has been started. So, if the watchdog dameon crashes, the system
64 will reboot after the timeout has passed.
66 Some other drivers will not disable the watchdog, unless a specific
67 magic character 'V' has been sent /dev/watchdog just before closing
68 the file. If the userspace daemon closes the file without sending
69 this special character, the driver will assume that the daemon (and
70 userspace in general) died, and will stop pinging the watchdog without
71 disabling it first. This will then cause a reboot.
75 All conforming drivers also support an ioctl API.
77 Pinging the watchdog using an ioctl:
79 All drivers that have an ioctl interface support at least one ioctl,
80 KEEPALIVE. This ioctl does exactly the same thing as a write to the
81 watchdog device, so the main loop in the above program could be
85 ioctl(fd, WDIOC_KEEPALIVE, 0);
89 the argument to the ioctl is ignored.
91 Setting and getting the timeout:
93 For some drivers it is possible to modify the watchdog timeout on the
94 fly with the SETTIMEOUT ioctl, those drivers have the WDIOF_SETTIMEOUT
95 flag set in their option field. The argument is an integer
96 representing the timeout in seconds. The driver returns the real
97 timeout used in the same variable, and this timeout might differ from
98 the requested one due to limitation of the hardware.
101 ioctl(fd, WDIOC_SETTIMEOUT, &timeout);
102 printf("The timeout was set to %d seconds\n", timeout);
104 This example might actually print "The timeout was set to 60 seconds"
105 if the device has a granularity of minutes for its timeout.
107 Starting with the Linux 2.4.18 kernel, it is possible to query the
108 current timeout using the GETTIMEOUT ioctl.
110 ioctl(fd, WDIOC_GETTIMEOUT, &timeout);
111 printf("The timeout was is %d seconds\n", timeout);
115 Some watchdog timers can be set to have a trigger go off before the
116 actual time they will reset the system. This can be done with an NMI,
117 interrupt, or other mechanism. This allows Linux to record useful
118 information (like panic information and kernel coredumps) before it
122 ioctl(fd, WDIOC_SETPRETIMEOUT, &pretimeout);
124 Note that the pretimeout is the number of seconds before the time
125 when the timeout will go off. It is not the number of seconds until
126 the pretimeout. So, for instance, if you set the timeout to 60 seconds
127 and the pretimeout to 10 seconds, the pretimout will go of in 50
128 seconds. Setting a pretimeout to zero disables it.
130 There is also a get function for getting the pretimeout:
132 ioctl(fd, WDIOC_GETPRETIMEOUT, &timeout);
133 printf("The pretimeout was is %d seconds\n", timeout);
135 Not all watchdog drivers will support a pretimeout.
137 Environmental monitoring:
139 All watchdog drivers are required return more information about the system,
140 some do temperature, fan and power level monitoring, some can tell you
141 the reason for the last reboot of the system. The GETSUPPORT ioctl is
142 available to ask what the device can do:
144 struct watchdog_info ident;
145 ioctl(fd, WDIOC_GETSUPPORT, &ident);
147 the fields returned in the ident struct are:
149 identity a string identifying the watchdog driver
150 firmware_version the firmware version of the card if available
151 options a flags describing what the device supports
153 the options field can have the following bits set, and describes what
154 kind of information that the GET_STATUS and GET_BOOT_STATUS ioctls can
155 return. [FIXME -- Is this correct?]
157 WDIOF_OVERHEAT Reset due to CPU overheat
159 The machine was last rebooted by the watchdog because the thermal limit was
162 WDIOF_FANFAULT Fan failed
164 A system fan monitored by the watchdog card has failed
166 WDIOF_EXTERN1 External relay 1
168 External monitoring relay/source 1 was triggered. Controllers intended for
169 real world applications include external monitoring pins that will trigger
172 WDIOF_EXTERN2 External relay 2
174 External monitoring relay/source 2 was triggered
176 WDIOF_POWERUNDER Power bad/power fault
178 The machine is showing an undervoltage status
180 WDIOF_CARDRESET Card previously reset the CPU
182 The last reboot was caused by the watchdog card
184 WDIOF_POWEROVER Power over voltage
186 The machine is showing an overvoltage status. Note that if one level is
187 under and one over both bits will be set - this may seem odd but makes
190 WDIOF_KEEPALIVEPING Keep alive ping reply
192 The watchdog saw a keepalive ping since it was last queried.
194 WDIOF_SETTIMEOUT Can set/get the timeout
196 The watchdog can do pretimeouts.
198 WDIOF_PRETIMEOUT Pretimeout (in seconds), get/set
201 For those drivers that return any bits set in the option field, the
202 GETSTATUS and GETBOOTSTATUS ioctls can be used to ask for the current
203 status, and the status at the last reboot, respectively.
206 ioctl(fd, WDIOC_GETSTATUS, &flags);
210 ioctl(fd, WDIOC_GETBOOTSTATUS, &flags);
212 Note that not all devices support these two calls, and some only
213 support the GETBOOTSTATUS call.
215 Some drivers can measure the temperature using the GETTEMP ioctl. The
216 returned value is the temperature in degrees farenheit.
219 ioctl(fd, WDIOC_GETTEMP, &temperature);
221 Finally the SETOPTIONS ioctl can be used to control some aspects of
222 the cards operation; right now the pcwd driver is the only one
223 supporting thiss ioctl.
226 ioctl(fd, WDIOC_SETOPTIONS, options);
228 The following options are available:
230 WDIOS_DISABLECARD Turn off the watchdog timer
231 WDIOS_ENABLECARD Turn on the watchdog timer
232 WDIOS_TEMPPANIC Kernel panic on temperature trip
234 [FIXME -- better explanations]
236 Implementations in the current drivers in the kernel tree:
238 Here I have tried to summarize what the different drivers support and
239 where they do strange things compared to the other drivers.
241 acquirewdt.c -- Acquire Single Board Computer
243 This driver has a hardcoded timeout of 1 minute
245 Supports CONFIG_WATCHDOG_NOWAYOUT
247 GETSUPPORT returns KEEPALIVEPING. GETSTATUS will return 1 if
248 the device is open, 0 if not. [FIXME -- isn't this rather
249 silly? To be able to use the ioctl, the device must be open
250 and so GETSTATUS will always return 1].
252 advantechwdt.c -- Advantech Single Board Computer
254 Timeout that defaults to 60 seconds, supports SETTIMEOUT.
256 Supports CONFIG_WATCHDOG_NOWAYOUT
258 GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
259 The GETSTATUS call returns if the device is open or not.
260 [FIXME -- silliness again?]
262 booke_wdt.c -- PowerPC BookE Watchdog Timer
264 Timeout default varies according to frequency, supports
267 Watchdog can not be turned off, CONFIG_WATCHDOG_NOWAYOUT
270 GETSUPPORT returns the watchdog_info struct, and
271 GETSTATUS returns the supported options. GETBOOTSTATUS
272 returns a 1 if the last reset was caused by the
273 watchdog and a 0 otherwise. This watchdog can not be
274 disabled once it has been started. The wdt_period kernel
275 parameter selects which bit of the time base changing
276 from 0->1 will trigger the watchdog exception. Changing
277 the timeout from the ioctl calls will change the
278 wdt_period as defined above. Finally if you would like to
279 replace the default Watchdog Handler you can implement the
280 WatchdogHandler() function in your own code.
282 eurotechwdt.c -- Eurotech CPU-1220/1410
284 The timeout can be set using the SETTIMEOUT ioctl and defaults
287 Also has a module parameter "ev", event type which controls
288 what should happen on a timeout, the string "int" or anything
289 else that causes a reboot. [FIXME -- better description]
291 Supports CONFIG_WATCHDOG_NOWAYOUT
293 GETSUPPORT returns CARDRESET and WDIOF_SETTIMEOUT but
294 GETSTATUS is not supported and GETBOOTSTATUS just returns 0.
296 i810-tco.c -- Intel 810 chipset
298 Also has support for a lot of other i8x0 stuff, but the
299 watchdog is one of the things.
301 The timeout is set using the module parameter "i810_margin",
302 which is in steps of 0.6 seconds where 2<i810_margin<64. The
303 driver supports the SETTIMEOUT ioctl.
305 Supports CONFIG_WATCHDOG_NOWAYOUT.
307 GETSUPPORT returns WDIOF_SETTIMEOUT. The GETSTATUS call
308 returns some kind of timer value which ist not compatible with
309 the other drivers. GETBOOT status returns some kind of
310 hardware specific boot status. [FIXME -- describe this]
312 ib700wdt.c -- IB700 Single Board Computer
314 Default timeout of 30 seconds and the timeout is settable
315 using the SETTIMEOUT ioctl. Note that only a few timeout
316 values are supported.
318 Supports CONFIG_WATCHDOG_NOWAYOUT
320 GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
321 The GETSTATUS call returns if the device is open or not.
322 [FIXME -- silliness again?]
324 machzwd.c -- MachZ ZF-Logic
326 Hardcoded timeout of 10 seconds
328 Has a module parameter "action" that controls what happens
329 when the timeout runs out which can be 0 = RESET (default),
330 1 = SMI, 2 = NMI, 3 = SCI.
332 Supports CONFIG_WATCHDOG_NOWAYOUT and the magic character
335 GETSUPPORT returns WDIOF_KEEPALIVEPING, and the GETSTATUS call
336 returns if the device is open or not. [FIXME -- silliness
339 mixcomwd.c -- MixCom Watchdog
341 [FIXME -- I'm unable to tell what the timeout is]
343 Supports CONFIG_WATCHDOG_NOWAYOUT
345 GETSUPPORT returns WDIOF_KEEPALIVEPING, GETSTATUS returns if
346 the device is opened or not [FIXME -- I'm not really sure how
347 this works, there seems to be some magic connected to
348 CONFIG_WATCHDOG_NOWAYOUT]
350 pcwd.c -- Berkshire PC Watchdog
352 Hardcoded timeout of 1.5 seconds
354 Supports CONFIG_WATCHDOG_NOWAYOUT
356 GETSUPPORT returns WDIOF_OVERHEAT|WDIOF_CARDRESET and both
357 GETSTATUS and GETBOOTSTATUS return something useful.
359 The SETOPTIONS call can be used to enable and disable the card
360 and to ask the driver to call panic if the system overheats.
362 sbc60xxwdt.c -- 60xx Single Board Computer
364 Hardcoded timeout of 10 seconds
366 Does not support CONFIG_WATCHDOG_NOWAYOUT, but has the magic
367 character 'V' close handling.
369 No bits set in GETSUPPORT
371 scx200.c -- National SCx200 CPUs
373 Not in the kernel yet.
375 The timeout is set using a module parameter "margin" which
376 defaults to 60 seconds. The timeout can also be set using
377 SETTIMEOUT and read using GETTIMEOUT.
379 Supports a module parameter "nowayout" that is initialized
380 with the value of CONFIG_WATCHDOG_NOWAYOUT. Also supports the
381 magic character 'V' handling.
383 shwdt.c -- SuperH 3/4 processors
385 [FIXME -- I'm unable to tell what the timeout is]
387 Supports CONFIG_WATCHDOG_NOWAYOUT
389 GETSUPPORT returns WDIOF_KEEPALIVEPING, and the GETSTATUS call
390 returns if the device is open or not. [FIXME -- silliness
393 softdog.c -- Software watchdog
395 The timeout is set with the module parameter "soft_margin"
396 which defaults to 60 seconds, the timeout is also settable
397 using the SETTIMEOUT ioctl.
399 Supports CONFIG_WATCHDOG_NOWAYOUT
401 WDIOF_SETTIMEOUT bit set in GETSUPPORT
403 w83877f_wdt.c -- W83877F Computer
405 Hardcoded timeout of 30 seconds
407 Does not support CONFIG_WATCHDOG_NOWAYOUT, but has the magic
408 character 'V' close handling.
410 No bits set in GETSUPPORT
412 w83627hf_wdt.c -- w83627hf watchdog
414 Timeout that defaults to 60 seconds, supports SETTIMEOUT.
416 Supports CONFIG_WATCHDOG_NOWAYOUT
418 GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
419 The GETSTATUS call returns if the device is open or not.
421 wdt.c -- ICS WDT500/501 ISA and
422 wdt_pci.c -- ICS WDT500/501 PCI
424 Default timeout of 60 seconds. The timeout is also settable
425 using the SETTIMEOUT ioctl.
427 Supports CONFIG_WATCHDOG_NOWAYOUT
429 GETSUPPORT returns with bits set depending on the actual
430 card. The WDT501 supports a lot of external monitoring, the
433 wdt285.c -- Footbridge watchdog
435 The timeout is set with the module parameter "soft_margin"
436 which defaults to 60 seconds. The timeout is also settable
437 using the SETTIMEOUT ioctl.
439 Does not support CONFIG_WATCHDOG_NOWAYOUT
441 WDIOF_SETTIMEOUT bit set in GETSUPPORT
443 wdt977.c -- Netwinder W83977AF chip
445 Hardcoded timeout of 3 minutes
447 Supports CONFIG_WATCHDOG_NOWAYOUT
449 Does not support any ioctls at all.