drivers/include/periph: add FREQM peripheral driver

[gompper]

Contribution description

This PR adds a peripheral driver for frequency meter (FREQM). Tested with SAM E54 XPLAINED PRO EVALUATION KIT (ATSAME54P20A microcontroller).

I think I have access to some other boards to test the driver in the near future.

Testing procedure

As the FREQM needs a reference clock to measure the frequency of another clock this test uses two internal clocks. The slower internal clock is used as reference to measure the faster internal clock.

The test can be invoked with:

make -C tests/periph/freqm flash

Expected result (via serial):

main(): This is RIOT! (Version: <INSERT VERSION HERE>)
FREQM peripheral driver test
Measured Clock Frequency: <MEASURED CLOCK FREQUENCY> Hz

[dylad]

Give it a quick try and it works nice !

[benpicco]

This is looking good!
Some nits and a suggestion to simplify the API:

[benpicco]

Suggested change

	#ifndef SAM0_GCLK_MAIN
	#define SAM0_GCLK_MAIN 0 /**< 120 MHz main clock */
	#endif
	#define SAM0_GCLK_MAIN 0 /**< 120 MHz main clock */

Main Clock is fixed to GCLK0

[gompper]

Is it possible that SAM0_GCLK_32KHZ is also fixed? When trying to overwrite it I didn't get any text on the terminal.

[benpicco]

It shoudln't be, unless it's hard-coded somewhere.
But maybe we should add some static_assert() to ensure no two GCLKs are configured to the same ID.

[benpicco]

Looks pretty good now!

[benpicco]

Looks good!
Only some minor nitpicks.

[riot-ci]

Murdock results

✔️ PASSED

b36e8e9 kconfigs/Kconfig.features: define periph_freqm

Success	Failures	Total	Runtime
7957	0	7957	10m:05s

Artifacts

• Documentation preview

[benpicco]

Looks good, thank you for your contribution!

[dylad]

Looks like something is missing with Kconfig.