SAML21 ticker only fires when set to 1ms. or higher

[janjongboom]

Description

I'm trying to update the SAML21 target to use Mbed OS 5 but I'm running into a weird issue (thanks unit tests!)... When setting a Timeout/Ticker object to tick with a timeout below 1 ms. the ticker does not fire. I assume it has something to do with the timer setup, but I don't know where to look. If I set the prescaler to 4 in us_ticker.c it works (at 500 us), but then everything runs at half speed, so not sure...

Issue request type

[X] Question
[ ] Enhancement
[ ] Bug

[janjongboom]

Potentially related: #2598

[ciarmcom]

Internal Jira reference: https://jira.arm.com/browse/MBOCUSTRIA-215

[cmonr]

@ARMmbed/mbed-os-core @ARMmbed/mbed-os-hal Thoughts?

[mprse]

Hi @janjongboom! I checked the PR and I think that you need to adapt us ticker driver to the new standards first. The requirements can be found here:

mbed-os/hal/us_ticker_api.h

Lines 30 to 104 in 51b8d6e

	/**
	* \defgroup hal_us_ticker Microsecond Ticker
	* Low level interface to the microsecond ticker of a target
	*
	* # Defined behavior
	* * Has a reported frequency between 250KHz and 8MHz - Verified by test ::us_ticker_info_test
	* * Has a counter that is at least 16 bits wide - Verified by test ::us_ticker_info_test
	* * All behavior defined by the @ref hal_ticker_shared "ticker specification"
	*
	* # Undefined behavior
	* * See the @ref hal_ticker_shared "ticker specification"
	*
	* @see hal_us_ticker_tests
	*
	* @{
	*/
	/**
	* \defgroup hal_us_ticker_tests Microsecond Ticker tests
	* Tests to validate the proper implementation of the microsecond ticker
	*
	* To run the microsecond ticker hal tests use the command:
	*
	* mbed test -t <toolchain> -m <target> -n tests-mbed_hal-common_ticker*,tests-mbed_hal-us_ticker*
	*
	* @see hal_ticker_tests
	*
	*/
	/**
	* \defgroup hal_ticker_shared Ticker Hal
	* Low level interface to the ticker of a target
	*
	* # Defined behavior
	* * The function ticker_init is safe to call repeatedly - Verified by test ::ticker_init_test
	* * The function ticker_init allows the ticker to keep counting and disables the ticker interrupt - Verified by test ::ticker_init_test
	* * Ticker frequency is non-zero and counter is at least 8 bits - Verified by ::ticker_info_test
	* * The ticker rolls over at (1 << bits) and continues counting starting from 0 - Verified by ::ticker_overflow_test
	* * The ticker counts at the specified frequency +- 10% - Verified by ::ticker_frequency_test
	* * The ticker increments by 1 each tick - Verified by ::ticker_increment_test
	* * The ticker interrupt fires only when the ticker times increments to or past the value set by ticker_set_interrupt.
	* Verified by ::ticker_interrupt_test and ::ticker_past_test
	* * It is safe to call ticker_set_interrupt repeatedly before the handler is called - Verified by ::ticker_repeat_reschedule_test
	* * The function ticker_fire_interrupt causes ticker_irq_handler to be called immediately from interrupt context -
	* Verified by ::ticker_fire_now_test
	* * The ticker operations ticker_read, ticker_clear_interrupt, ticker_set_interrupt and ticker_fire_interrupt
	* take less than 20us to complete - Verified by ::ticker_speed_test
	*
	* # Undefined behavior
	* * Calling any function other than ticker_init before the initialization of the ticker
	* * Whether ticker_irq_handler is called a second time if the time wraps and matches the value set by ticker_set_interrupt again
	* * Calling ticker_set_interrupt with a value that has more than the supported number of bits
	* * Calling any function other than us_ticker_init after calling us_ticker_free
	*
	* # Potential bugs
	* * Drift due to reschedule - Verified by ::ticker_repeat_reschedule_test
	* * Incorrect overflow handling of timers - Verified by ::ticker_overflow_test
	* * Interrupting at a time of 0 - Verified by ::ticker_overflow_test
	* * Interrupt triggered more than once - Verified by ::ticker_interrupt_test
	*
	* @ingroup hal_us_ticker
	* @ingroup hal_lp_ticker
	*/
	/**
	* \defgroup hal_ticker_tests Ticker Tests
	* Tests to validate the proper implementation of a ticker
	*
	* To run the ticker hal tests use the command:
	*
	* mbed test -t <toolchain> -m <target> -n tests-mbed_hal-common_ticker*
	*
	* @ingroup hal_us_ticker
	* @ingroup hal_lp_ticker
	*/

You can run the following tests to check the us ticker driver:

• tests-mbed_hal-common_tickers
• tests-mbed_hal-common_tickers_freq
• tests-mbed_hal-us_ticker

Generally I suggest to start with specifying the counter frequency and size used to handle the us ticker. This is required by the higher layer. If not specified, then default values are used (1MHz/32bits). Example can be found below. You can also use this file as pattern.

mbed-os/targets/TARGET_NORDIC/TARGET_NRF5x/us_ticker.c

Lines 49 to 57 in 51b8d6e

	/* us ticker is driven by 1MHz clock and counter length is 16 bits. */
	const ticker_info_t* us_ticker_get_info()
	{
	static const ticker_info_t info = {
	US_TICKER_FREQ,
	US_TICKER_COUNTER_BITS
	};
	return &info;
	}

[janjongboom]

@mprse, Thanks! Will take a look. Hope this will get me a bit further, although there seems to be an underlying issue with the IRQ firing on the Atmel.