alif: implement machine.PWM support

[dpgeorge]

Summary

This PR adds machine.PWM support to the alif port. It uses the existing common machine bindings and implements the standard set of functionality.

It uses the UTIMER peripheral and makes PWM available on all pins that have an alt function connection to a UTIMER, which is 54 pins (see below about UTIMER11).

Testing

Tested on ALIF_ENSEMBLE and OPENMV_AE3, using an oscilloscope, fading LEDs and the existing tests/extmod_hardware/machine_pwm.py test.

Sample test code that works on both alif boards:

import time, machine
p = machine.PWM("LED_RED", invert=True)
p.freq(1000)
for _ in range(10):
    for duty in range(101):
        p.duty_ns(duty * 10000)
        time.sleep_ms(10)

Trade-offs and Alternatives

This uses the UTIMER peripheral, but not UTIMER11 which is already in use by the HE core for its systick timer. So the following pins don't have PWM available because they need UTIMER11: P2_6, P2_7, P7_6, P7_7, P12_6, P12_7. For OPENMV_AE3, none of those pins are exposed to the user so they don't need PWM.

For the implementation I tried to use the Alif SDK driver, but it's quite limited so most of the code here uses direct register reads/writes.

[dpgeorge]

@iabdalkader @kwagyeman FYI

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.42%. Comparing base (bebb404) to head (95b3e72).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #18799   +/-   ##
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  Coverage   98.42%   98.42%           
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  Files         174      174           
  Lines       22331    22331           
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  Hits        21980    21980           
  Misses        351      351           

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[kwagyeman]

@dpgeorge - I have time to test this PR and #18776 tomorrow. Sorry about not getting on it immediately.

[dpgeorge]

No hurry!

[kwagyeman]

@dpgeorge - Works great! Tested on all pins.

Also, ever think about adding this to the standard lib? https://github.com/redoxcode/micropython-servo. It would make folks lives easier to be able to use this for servo control.

[dpgeorge]

Works great! Tested on all pins.

Great, thanks for testing.

Also, ever think about adding this to the standard lib? ...

No, I didn't see that servo driver before. It looks simple but useful.

We do have pyb.Servo() which allows driving a servo to a set position over a period of time (in the background updating the PWM gradually). I would like to generalise that driver to all the ports, but it's not really a priority at the moment.

In the meantime, people could easily install that servo Python driver.

[kwagyeman]

@dpgeorge - Okay, feel free to merge.