cpu/qn908x: Add timer driver based on CTIMER.

[iosabi]

Contribution description

The QN908x CPU has several timer modules: one RTC (Real-Time Clock) that
can count from the 32kHz internal clock or 32.768 kHz external clock,
four CTIMER that use the APB clock and have four channels each and one
SCT timer with up to 10 channels running on the AHB clock.

This patch implements a timer driver for the CTIMER blocks only, which
is enough to make the xtimer module work. Future patches should improve
on this module to support using the RTC CNT2 32-bit free-running
counter unit and/or the SCT timer.

Testing procedure

./dist/tools/compile_and_test_for_board/compile_and_test_for_board.py . qn9080dk --jobs=1 --with-test-only --applications 'tests/xtimer_*'

Issues/PRs references

This is part of issue #13852.

[benpicco]

looks good - does this need any board config?
Ah does't seems so - the timers are always sourced by the same clock - reminds me of lpx23xx 😉

[benpicco]

Ah this exposed some bugs/omissions in the watchdog & gpio driver since those tests were previously not build.

[iosabi]

Ah this exposed some bugs/omissions in the watchdog & gpio driver since those tests were previously not build.

That seems to be the issue.

GPIO_BOTH (both rising and falling edges) doesn't seem to be supported by the hardware. I can either set rising, falling, low or high. I could try to emulate this by setting one edge or the other one based on the current level, but I think it might not be all that robust. I'll try.

UART_DATA_BITS_5 and UART_DATA_BITS_6, the MCU supports 7, 8 and 9 bits. How can I signal that those are not supported?

[benpicco]

GPIO_BOTH (both rising and falling edges) doesn't seem to be supported by the hardware. I can either set rising, falling, low or high. I could try to emulate this by setting one edge or the other one based on the current level, but I think it might not be all that robust. I'll try.

you could also chose to not support it and return error when trying to configure it.

UART_DATA_BITS_5 and UART_DATA_BITS_6, the MCU supports 7, 8 and 9 bits. How can I signal that those are not supported?

stm32 just marks them as not supported and then fails uart_mode if those are set.

[iosabi]

I added a second commit (first in the stack) to this pull request that should address gpio, uart and wdt.

I see most CPUs treat NWDT_TIME_LOWER_LIMIT as non-inclusive (assert(NWDT_TIME_LOWER_LIMIT < max_time) or similar). This is a bit more restrictive than it should be. We could actually set 0 if we wanted the WDT to trigger immediately. Right now the lowest max_time is 2, because that constant can't be 0.