$home/manuals/plan9_4th/3/wd

WD(3)                      Library Functions Manual                      WD(3)



NAME
       wd - hardware watchdog timer

SYNOPSIS
       bind -a #w /dev
       /dev/wdctl

DESCRIPTION
       This device presents textual information about hardware watchdog timers
       on PCs and some other machines, and allows user-level control of  them.
       When  enabled,  a  watchdog timer counts to zero in a few seconds; upon
       reaching zero, it resets the machine with an NMI or  equivalent.   Some
       process  must  periodically  restart  the watchdog to avoid the NMI and
       keep the system alive; watchdog(8) is one such program.

       Reads from wdctl yield data of this form:

              enabled 3 restarts

       or

              disabled 3 restarts

       Control messages may be written to wdctl and include and

       The watchdog is disabled at system shutdown, and  when  the  last  open
       file descriptor for wdctl is closed.

SOURCE
       /sys/src/9/port/devwd.c
       /sys/src/9/*/*watchdog.c

SEE ALSO
       proc(3), watchdog(8)

BUGS
       On  PCs, to ensure consistent use of one CPU's timers, an message wires
       the issuing process (see proc(3)) to a CPU, and any subsequent  control
       messages will wire the issuing processes to that same CPU.



                                                                         WD(3)