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RTC

Implementing RTC enables Mbed OS to keep track of the current time. The standard library time keeping functions, such as time, use it.

Assumptions

Defined behavior

The function rtc_init is safe to call repeatedly.
RTC accuracy is at least 10%.
Init/free doesn't stop RTC from counting.
Software reset doesn't stop RTC from counting.
Sleep modes don't stop RTC from counting.
Shutdown mode doesn't stop RTC from counting.

Undefined behavior

Calling any function other than rtc_init before the initialization of the RTC.

Notes

Watch out for these common trouble areas when implementing this API:

Incorrect overflow handling.
Glitches due to ripple counter.

Dependencies

Hardware RTC capabilities.

Implementing the RTC API

You can find the API and specification for the RTC API in the following header file:

RTC hal

To enable RTC support in Mbed OS, add the RTC label in the device_has option of the target's section in the targets.json file.

Testing

The Mbed OS HAL provides a set of conformance tests for RTC. You can use these tests to validate the correctness of your implementation. To run the RTC HAL tests, use the following command:

mbed test -t <toolchain> -m <target> -n "tests-mbed_hal-rtc*"

You can read more about the test cases:

RTC hal tests

RTC