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Testing the watchdog
23.4 Testing the watchdog
For IEC 60730 and other safety standards, the expectation is that anything that monitors a
safety function must be tested, and this test is required to be fault tolerant. To test the
watchdog, its main timer and its associated compare and reset logic must be tested. To
this end, two tests are implemented for the watchdog, as described in
Byte
Test. A control bit is provided to put the watchdog into functional test mode. There
is also an overriding test-disable control bit which allows the functional test mode to be
disabled permanently. After it is set, this test-disable bit can only be cleared by a reset.
These two tests achieve the overall aim of testing the counter functioning and the
compare and reset logic.
Do not enable the watchdog interrupt during these tests. If
required, you must ensure that the effective time-out value is
greater than WCT time. See
more details.
To run a particular test:
1. Select either quick test or byte test..
2. Set a certain test mode bit to put the watchdog in the functional test mode. Setting
this bit automatically switches the watchdog timer to a fast clock source. The
switching of the clock source is done to achieve a faster time-out and hence a faster
test.
In a successful test, the timer times out after reaching the programmed time-out value and
generates a system reset.
After emerging from a reset due to a watchdog test, unlock and
configure the watchdog. The refresh and unlock operations and
interrupt are not automatically disabled in the test mode.
470
Note
Generated Resets and Interrupts
Note
K30 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Quick Test
and
for
Freescale Semiconductor, Inc.
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