esp32/machine_timer: Add find free timer id.

[IhorNehrutsa]

atimer = Timer(-2)
The constructor id of -2 selects the id of a free timer.
Check the timer id range.
Check if the timer is already in use.

This allows you to write separated library modules without worrying about the timer id. For example:

class DoSomethingByTymer():
    def init(self):
        self.timer = Timer(-2, mode=Timer.PERIODIC, period=5000, callback=self.cb)
    def cb(self):
        print('DoSomethingByTymer()')
        # etc

EDITED: Maybe id value None is a better arg?
atimer = Timer(None)

[IhorNehrutsa]

Check if the timer is already in use:

from machine import Timer

t0 = Timer(0)
t1 = Timer(0)

Traceback (most recent call last):
File "", line 4, in
RuntimeError: already used

Check the timer id range:

from machine import Timer

t = Timer(10)

Traceback (most recent call last):
File "", line 3, in
ValueError: id must be from 0 to 4

Timer() constructor id of -2 selects the id of a free timer:

from machine import Timer

t0 = Timer(-2)
print(t0)

t1 = Timer(-2)
print(t1)

t2 = Timer(-2)
print(t2)

t3 = Timer(-2)
print(t3)

t4 = Timer(-2)

Timer(3, mode=ONE_SHOT, period=0)
Timer(2, mode=ONE_SHOT, period=0)
Timer(1, mode=ONE_SHOT, period=0)
Timer(0, mode=ONE_SHOT, period=0)
Traceback (most recent call last):
File "", line 15, in
RuntimeError: out of Timers:4

[projectgus]

This is an automated heads-up that we've just merged a Pull Request
that removes the STATIC macro from MicroPython's C API.

See #13763

A search suggests this PR might apply the STATIC macro to some C code. If it
does, then next time you rebase the PR (or merge from master) then you should
please replace all the STATIC keywords with static.

Although this is an automated message, feel free to @-reply to me directly if
you have any questions about this.

[cnadler86]

Is this still ongoing? I think it might ve a very helpful feature, since sw timers are not supported on esp32 Boards

[projectgus]

Is this still ongoing? I think it might ve a very helpful feature, since sw timers are not supported on esp32 Boards

Sorry @IhorNehrutsa that no one has gotten back to you about this, and thanks @cnadler86 for the heads up.

In general, it's better if MicroPython APIs behave the same across ports. If I understand correctly, the main reason for adding this special -2 value on esp32 port is precisely because software timers aren't supported on esp32. There's probably not really a need for it on the ports with software timers.

So the way forward for machine.Timer on the esp32 port is probably to implement software timers, so it works the same as other ports with software timer support. I don't think there's any technical barrier to doing this, the ESP-IDF framework has the esp_timer API which can create a microsecond precision timer callback, and the shared/runtime/softtimer.[ch] code has all the code to implement Python soft timers on top of a lower level primitive like that. Someone just needs to do that work and submit the PR (AFAIK there is not any open PR for this, yet).

[projectgus]

I'm going to close this out, but please refer to comment above - a PR that implements softtimers on esp32 port would be very welcome (I think probably using esp_timer API).