PCIe-WDG-CSM

Details

Two Models

• The PCIe-WDG-CSM card contains a watchdog timer and on-card RGB LED and speaker alarm to signal watchdog timeout. A DPDT relay, two LVTTL inputs and two outputs, and fused 3.3V general purpose outputs and ground are accessed via the DB25 female I/O connector on the card mounting bracket.
• An advanced model, the PCIe-WDG-CSMA, is also available which includes sensors to monitor the PCI Express Bus power supply, internal temperature and humidity, and ambient light, and comes with a remote temperature sensor on a 19” cable. A pair of opto-isolated digital outputs and four opto-isolated digital inputs are available for general purpose use, and are great for eliminating troublesome ground loops and transients in electrically noisy environments.

Both of these models allow various “Actions” to be taken in response to “Events”, which are changes in the status of the various sensors. An example Action, such as de-energizing the relay, can be tied to a particular Event, such as an input bit that isn’t pulsing fast enough. All of this is configurable through an easy-to-use Windows Graphical Settings program, or under application control via the rich API provided in both Windows DLL and Linux Shared Object forms — with full source code provided, of course.

What is a Watchdog?

Watchdog Timers provide a last line of defense against system lockups that can cause real damage — physical damage, as when a closed-loop control system stops receiving or sending updates causing bearings to melt or boilers to explode — but also damage to a brand or to customer relationship, such as when a retail Kiosk application experiences intermittent BSoDs preventing the Kiosk from being used, and causing maintenance nightmares for the retail establishment. These kinds of problems are eliminated when a Watchdog is on duty. The Watchdog monitors signals produced by the application or its environment. The ongoing recurrence of these signals, called a “Pet” or “Petting” of the Watchdog, keeps the Watchdog satisfied that all is well, and there’s no need to raise an alarm. However, if the Watchdog is not Pet often enough it Growls, warning everyone present that something may be amiss. If the Growl doesn’t successfully cause the Petting to resume, the Watchdog Barks. In the case of the PCIe-WDG-CSMA the most common result of a Bark is to reset the host PC, rebooting it as if the Reset button had been tapped — but a wide variety of other Actions can be taken, either when the Watchdog Growls or Barks, but also in response to other Events.

Guard Dogs vs Patrol Dogs

The most robust Watchdogs are trained to respond to only your commands. You accomplish this by adding “Watchdog Pet” instructions (part of our API, see Chapter 5) to your application code, explicitly informing the PCIe-WDG-CSM(A) that your critical code hasn’t locked up by Petting the Watchdog before it Growls. This can be likened to setting a Watchdog to Guard a specific valuable: if someone opens this safe, sound the alarm! :: If my application doesn’t issue a Watchdog Pet instruction at least once a second, Growl! Sometimes it isn’t practical to modify a critical application, whether it be legacy code long lost, it was written by a 3^rd party and not open-source, or it being simply too expensive to contemplate! In these cases the Watchdog can monitor the environment rather than waiting to be explicitly pet by code added to the application. For example, an external signal can be monitored: the Watchdog would Growl if a closed-loop control application stops sending digital output data, perhaps. In these cases, the Watchdog is “Pet” by the changing digital outputs, rather than explicitly by changes to the application code. This use of a Watchdog is akin to putting a Watchdog on patrol in the parking lot: it will not notice when the safe is opened, but would react to the breaking of a window…something that may not actually be related to protecting the safe at all (perhaps neighborhood kids hit a home-run ball through the window). Thus the “Patrol Watchdog” technique can lead to false-positives, and in the worst-cases some false-negative reports as well (maybe the safe cracking bad-guys came in through a basement tunnel, which the Patrol Watchdog didn’t know existed!) On the other hand, when the critical application source code is not modifiable, putting a Watchdog on Patrol can cover most scenarios — and our PCIe-WDG-CSM(A) can monitor multiple sensors simultaneously, providing potentially overlapping zones of coverage. The Watchdog’s patience — that is, how many seconds or minutes the Watchdog will wait between Pets before Growling, and eventually Barking — is configurable through API calls or as part of the Windows Settings program, and is stored with all other Event / Action configuration data in non-volatile memory on the device.

Downloads