A watchdog timer is a computer hardware timing device that triggers a system reset if the main program, due to some fault condition, such as a hang, neglects to regularly service the watchdog (writing a “service pulse” to it, also referred to as “petting the dog”). The intention is to bring the system back from the hung state into normal operation. A BlueGene supercomputer cabinet. ... Look up reset in Wiktionary, the free dictionary. ... A computer program is a collection of instructions that describe a task, or set of tasks, to be carried out by a computer. ... This page is about the computer malfunction called hanging. ...

Watchdog timers may be more complex, attempting to save debug information onto a persistent medium; i.e. information useful for debugging the problem that caused the fault. In this case a second, simpler, watchdog timer ensures that if the first watchdog timer does not report completion of its information saving task within a certain amount of time, the system will reset with or without the information saved. The most common use of watchdog timers is in embedded systems, where this specialized timer is often a built-in unit of a microcontroller. Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware thus making it behave as expected. ... It has been suggested that Embedded System Design in an FPGA be merged into this article or section. ... It has been suggested that this article or section be merged with embedded microprocessor. ...

Watchdog timers may also trigger control systems to move into a safety state, such as turning off motors, high-voltage electrical outputs, and other potentially dangerous subsystems until the fault is cleared.

For example, a watchdog timer can be implemented with a x-bit counter in a system working with a clock signal of y MHz, therefore, the system will shut down if the timer is not reset in a period of seconds. In general, a counter is a device which stores (and sometimes displays) the number of times a particular event or process has occurred, often in relationship to a clock signal. ... In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ...

See also

• Immunity Aware Programming
• Power distribution unit
• System time

// For devices containing a microconroller the design of firmware impacts the EMC performance of the system. ... A Power distribution unit (Commonly abbreviated to PDU) is a device that distributes electric power. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ...

External links

• One design for a hardware watchdogPDF (6.62 KiB)