watchdogtimers

A watchdog timer is a hardware or software timer that ensures a computer system can recover from faults by triggering a predefined corrective action if the software fails to service or respond within a specified interval. The primary purpose is to detect malfunctions such as software hangs, deadlocks, or stalled hardware and to initiate a recovery, typically a system reset or a safe interrupt.

In operation, the watchdog is started with an initial timeout period. The running software must regularly reset, service, or “kick” the timer before it expires. If the timer expires, it asserts a reset signal, generates an interrupt, or raises a fault condition, depending on the design. Some implementations support windowed modes, where the reset must occur within a specific time window to avoid false alarms.

Watchdog timers come in hardware, software, or mixed forms. Hardware watchdogs are built into microcontrollers or external chips and are generally more independent of software state; software watchdogs run as part of an operating system or application layer and rely on normal software timing. Many systems offer configurable timeout values, action types (reset, interrupt, or both), and sometimes multiple stages or chained watchdogs.

Common applications are in embedded systems, automotive and industrial controllers, servers, and safety-critical equipment where unattended operation is expected. Design considerations include selecting appropriate timeout periods, ensuring watchdog servicing cannot be easily bypassed, testing under fault conditions, and handling reset states in a predictable manner. The goal is a reliable mechanism that enables automatic recovery with minimal data loss and downtime.