lp_ticker test is not compatible with unified sleep implementation

[stevew817]

The lp_ticker test in TESTS/mbed-hal is fundamentally incompatible with the unified sleep API in use by Silicon Labs targets.

At

mbed-os/TESTS/mbed_hal/lp_ticker/main.cpp

Line 97 in 3a16ca9

sleep();

there is a call to sleep(), which will turn off us_ticker on Silicon Labs platforms, since there is no object initialized that is using the high-power, high-resolution ticker. Therefore, the us_ticker_read function is not suitable for tracking time across sleep calls.

Please change this test to rely on the RTC as an always-on clock, or use us_ticker properly and set it to timeout after the lp_ticker is expected to return.

[bridadan]

cc @bulislaw

[bulislaw]

@stevew817 could you provide a patch, that uses the us_ticker properly on Silicon Labs platforms?

[ghost]

GitHib issue review: Closed due to inactivity. Please re-file if critical issues found.