Watchdog Timer Card FAQ
What's a Watchdog Timer?
A watchdog timer is a mechanism that is used to determine whether
another mechanism is functioning properly. In terms of the ET/WDT
card, it is an ISA bus compatible card with a built-in hardware
timer that is capable of issuing a hardware reset and rebooting
a PC.
Why Would I Want to Hard Reboot My PC?
If you're a service provider, or you have system that runs when
there is no operator physically on-site, there are times when
a PC running UNIX may hang, or when some process that is necessary
stops working. The watchdog timer can detect this in a matter
of seconds or minutes (before your customers start complaining)
and reboot the PC.
The ET/WDT also has a "demand boot" feature, which allows
a remote operator to hard reboot the PC via a dial-up or TELNET
session. Some PCs or adapter cards will not reset properly (or
may hang) when a soft reboot is issued, but with the watchdog
timer card the PC will be hard booted, just as if you pushed the
physical reset button.
How Does it Work?
The ET/WDT is an ISA card with a hardware timer that wires directly
into the reset switch on the PC. Think of the watchdog timer as
a time bomb with a reset button. Once you set the timer, it counts
down until a timeout occurs. If a timeout occurs, the bomb explodes
(BOOM!). Of course the watchdog timer doesn't explode..it pulls
the reset pins on your motherboard and reboots the PC. A simple
utility is provided which sets the watchdog timer to reboot the
PC after X seconds (where X is 0 to 2500) if not notified before
the timer expires.
Of course the goal is to NOT reset the PC unless something is
wrong. The basic driver supplied with the board uses an on-board
interrupt which notifies the watchdog timer once per second that
the system is alive. With each notification, the timer is reset,
so unless there is no notification for X seconds the system runs
as usual. The theory behind this is that as long as the system
is processing interrupts, it is not hanging. If you wish you
can remove the interrupt jumper on the board and write your own
daemon or script that resets the watchdog timer yourself. Your
script can check the sanity of the system and reset the timer if
all is well. This way you can also shut down your system gracefully.
Additionally, running the utility with a timeout value of 0 physically
boots the PC on demand. If you have a machine that needs to be
physically reset whenever it is rebooted you can modify your shutdown
procedure to have the watchdog reboot the machine.
What Drivers Are Available?
Drivers for the stand-alone watchdog timer card (ET/WDT) are available
for BSD/OS and FreeBSD. Our ET/5021 and ET/5025 card has a watchdog
timer on-board and is available for BSD/OS, FreeBSD and Linux.
How Can I Use the Watchdog Timer in My Application
A 'C' language development disk is available with a sample program
and source code that illustrates how to use the watchdog timer.
You can add the watchdog timer code to any existing application
with just a few lines of 'C' code!
How Much Does it Cost?
ET/WDT Stand-alone Watchdog Timer. Quantity 1 - $195....2+ 169....5+
$149.
ET/5021 V.35 Com Board with on-board WDT Quantity 1 - $595.
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