TWDT0 is loaded with a new value and the counter restarts counting with
it by written RST bit in Timer Control register (T0CSR) to 1. Then, the
RST bit in T0CSR register is cleared automatically on the 2nd rising
edge of T0IN clock. Since TWCP is set to 1:32, the maximum time that RST
bit is unset is 32 * (1 / 32768) ~= 980us.
Polling this bit within a critical section in current npcx watchdog
driver isn't a good approach since it might block the other interrupts
need to service them in time. This CL introduces a timeout mechanism and
removes the critical section to improve this disadvantage. Consider the
clock tolerance, 2 ms is a suitable timeout value for RST bit. We also
remove polling for WD_RUN bit in T0CSR. Npcx watchdog needs serval LFCLK
(32k Hz) clocks to stop watchdog. 1 ms is long enough for the timeout
mechanism.
Signed-off-by: Mulin Chao <mlchao@nuvoton.com>
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