NXP Kinetis KV5x Watchdog Clocking

Published by Tim Allen on 1st Nov 2021

The NXP MKV56F1M0Vxx24 is a 240 MHz Cortex-M7 based MCU for real-time, high performance connected control. We have incorporated this microcontroller into a new high-performance camera motion control product for the film industry. During development, we ran into an issue where the watchdog would almost always time-out. The watchdog was being refreshed frequently, and under certain situations (where we were doing a lot of I/O) the watchdog was perfectly happy.

By default, the watchdog is clocked by a 1 kHz Low Power Oscillator, which is independent of the processor clock. The issue turned out to be that if the watchdog is refreshed at a rate of 1 kHz or more when clocked from the LPO, the refreshes are completely ignored. The solution was to clock the watchdog from the bus clock. The MKV56F1M0Vxx24 reference manual, although devoting a whole section to “Restrictions on Watchdog Operation”, does not mention this particular one.

Categories: Development