SLAU847D October 2022 – May 2024 MSPM0L1105 , MSPM0L1106 , MSPM0L1227 , MSPM0L1228 , MSPM0L1228-Q1 , MSPM0L1303 , MSPM0L1304 , MSPM0L1304-Q1 , MSPM0L1305 , MSPM0L1305-Q1 , MSPM0L1306 , MSPM0L1306-Q1 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346 , MSPM0L2227 , MSPM0L2228 , MSPM0L2228-Q1
The analog startup health test is run by application software when powering up the TRNG module. This test verifies that the analog block is functioning properly by capturing 4,096 consecutive analog samples and verifying that the samples pass a health test.
If the health test fails, the health fail (IRQ_HEALTH_FAIL) and command done (IRQ_CMD_DONE) interrupts are both asserted, and the TRNG state machine enters the ERROR state. The result of the analog start up self-test is also reported in the ANA_TEST bit in the TEST_RESULTS register. If the test passed, the ANA_TEST bit is set. If the test failed, the ANA_TEST bit is left cleared.
If the test does fail, this indicates that a severe loss of entropy in the analog block was detected during the test. This means that the entropy source can not be used in its current state. The probability of this test returning a false positive (probability that a failure was asserted but the analog block is operating correctly) is statistically very low, but not zero. This means that there is a small probability that a failure could be indicated in certain cases even if the TRNG analog block is operating correctly. To ensure that a test failure is legitimate and that there is not a loss of entropy, the analog startup health test can be repeated to validate the failure. In the event of a failure, the following procedure is recommended: