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1b2f6e3d1f
Currently the mimxrt port has a resolution of only 1 second for `machine.RTC().datetime()` and `time.time_ns()`. This means (among other things) that it fails the `tests/extmod/time_time_ns.py` test, which requires requires at least 5ms of resolution. The underlying RTC hardware is just a 64-bit counter, and the HAL functions `SNVS_LP_SRTC_GetDatetime()` and `SNVS_LP_SRTC_SetDatetime()` do conversions between y/m/d/h/m/s and this 64-bit value, which counts at a rate of 32kHz. This commit changes the RTC code to access the 64-bit counter directly and therefore improve resolution of all RTC functions to 1/32768 seconds. That makes things much simpler because it a lot of places the code wants to know the number of seconds since the Epoch. Currently it uses a combination of `SNVS_LP_SRTC_GetDatetime()` and `timeutils_seconds_since_epoch()` which converts the 64-bit counter to date-time and then back to seconds. Those operations are computationally expensive. With this commit, getting the number of seconds since the Epoch is as simple as reading the 64-bit counter and dividing by 32768. We can leverage a lot of the timeutils functions to simplify everything, and make it similar to other ports like rp2. Benefits of this change: - simpler, more efficient code to get/set RTC - `machine.RTC().datetime()` now has a non-zero value in the last slot, being the number of microseconds, and has a resolution of 1/32768 seconds - `time.time_ns()` now has a resolution of 1/32768 seconds - the `test/extmod/time_time_ns.py` test now passes Signed-off-by: Damien George <damien@micropython.org>