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Improve comments about the time_delay test.

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Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
This commit is contained in:
Jerry Yu 2023-04-19 14:07:59 +08:00
parent ed9b9a7579
commit d3c7d538f1
1 changed files with 12 additions and 11 deletions
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23
tests/suites/test_suite_platform.function
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@ -91,20 +91,21 @@ void time_delay_seconds(int delay_secs)
elapsed_secs = mbedtls_time(NULL) - current;
/*
* `mbedtls_time` was defined as c99 function `time`, it uses
* CLOCK_REALTIME and returns the number of seconds since the Epoch. And
* `nanosleep` uses CLOCK_MONOTONIC. The time sources are out of sync.
* `mbedtls_time()` was defined as c99 function `time()`, returns the number
* of seconds since the Epoch. And it is affected by discontinuous changes
* from automatic drift adjustment or time setting system call. The POSIX.1
* specification for clock_settime says that discontinuous changes in
* CLOCK_REALTIME should not affect `nanosleep()`.
*
* If CLOCK_MONOTONIC is faster than CLOCK_REALTIME and `nanosleep` exits at
* the end of a second, `elapsed_secs` will be less than `delay_secs`.
* If discontinuous changes occur during `nanosleep()`, we will get
* `elapsed_secs < delay_secs` for backward and `elapsed_secs > delay_secs`
* for forward.
*
* Workaround it with 1 second tolerance.
* The following tolerance windows cannot be guaranteed.
* PLEASE DO NOT ENABLE IT IN CI TEST.
*/
TEST_ASSERT(elapsed_secs >= delay_secs - 1);
/* If CLOCK_MONOTONIC is slower than CLOCK_REALTIME or nanosleep does not
* exit on time.
*/
TEST_ASSERT(elapsed_secs < 4 + delay_secs);
TEST_ASSERT(elapsed_secs - delay_secs >= -1 &&
elapsed_secs - delay_secs < 4);
/* This goto is added to avoid warnings from the generated code. */
goto exit;
}