| Computers and programs that need to run | | | | There are unlimited application areas that would |
| continuously will eventually malfunction and lock up. | | | | benefit by having a watchdog timer installed in a |
| When a computer or program malfunctions it | | | | computer. Some examples of them are: |
| could cause unintended results or damage. Even if | | | | - Medical systems: Non-critical medical monitoring |
| it just locks up, an unattended or remote | | | | systems that collect patient data continuously. |
| computer could be down for days potentially | | | | - Telecom systems: IVR or voice mail systems |
| resulting in loss of sales for a device like a kiosk. | | | | for example. |
| An OS watchdog timer provides a hardware | | | | - Video surveillance: Security and loss prevention |
| means to do an automatic reboot on the | | | | systems. |
| computer. | | | | - Kiosks: Such as those in airports, malls and other |
| Some of the more common reasons a computer | | | | locations that provide information or sell products |
| will malfunction: | | | | and services. |
| - The hardware freezes: Typically you will see this | | | | - Remote or inhospitable areas: Computers used |
| when there is a power glitch or if the computer | | | | for data collection in systems like remote weather |
| overheats because of a fan failure. | | | | stations or factory process monitoring. |
| - The OS crashes: On a Windows machine this is | | | | Watchdog timers are available to interface with |
| the classic Blue Screen of Death or BSOD. | | | | most buses or I/O ports on a computer. The |
| - A device driver malfunctions: There are so | | | | most common are those for PCI, PCIe (Express), |
| many drivers running on a typical computer | | | | USB, Serial RS-232. The watchdog timer is |
| interacting with each other that there is a | | | | "tickled" by simply accessing an I/O port on the |
| possibility of failure. | | | | device or via a communications packet. The |
| - The application program stops or crashes: The | | | | "tickling can be done with a stand-alone program |
| OS might detect something in your application | | | | supplied by the OS watchdog vendor or it can be |
| program under certain conditions that causes it to | | | | done by simply adding a few lines of code to |
| be stopped. | | | | your existing application and then linking with a |
| An OS hardware watchdog works by setting a | | | | vendor-supplied library. |
| count down timer to run. This time could | | | | Some watchdog timers are available with |
| anywhere from several seconds up to several | | | | additional reporting capability such as the number |
| hours. It is then the responsibility of the application | | | | of times a computer has been restarted which |
| program or a utility program on the computer to | | | | could very helpful to diagnose and identify |
| go out and "tickle" the watchdog timer on a | | | | computers that lock up too frequently. OS |
| regular basis. Each time the watchdog gets | | | | watchdogs are also available with non-volatile |
| "tickled" it reloads the count down timer and | | | | memory options that allow a user to fine-tune the |
| starts over. When the application program or | | | | operating parameters of the device. Many |
| computer malfunctions the "tickles" stop and the | | | | versions are available with additional relays, |
| watchdog eventually counts down to zero and | | | | temperature monitoring, digital I/O, and even |
| does an automatic reboot of the computer. | | | | external digital inputs to "tickle" the timer. |