Automotive Semiconductors and Functional Safety
Which correctly describes a feature of a window watchdog timer?
- AOnce kicked, it stops monitoring to reduce power consumption
- BIt detects as an anomaly not only kicks (timer clears) that come too late relative to a defined time window but also kicks that come too early
- CWhen a kick is late, it assumes the program is doing heavy processing and, without resetting, automatically extends the wait time to let processing continue
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Answer: B. It detects as an anomaly not only kicks (timer clears) that come too late relative to a defined time window but also kicks that come too early
An ordinary watchdog issues a reset if it is not kicked within a certain time. However, in anomalies where the program skips part of its processing and runs in a short loop, kicks arrive early and may go unnoticed. A window watchdog defines a time window in which kicking is allowed and treats kicks that are too early or too late as anomalies. In automotive systems, the watchdog is sometimes placed in an external monitoring IC running on a clock separate from the microcontroller, so that a common cause does not stop both.
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