analogWrite - PWM frequency and resolution

[ThomasManz]

Hello,

I wanted to create a PWM signal with 20 ms period / 50 Hz for an average servo motor. I´m aware that only frequencies above 100 Hz are officially supported, so I´ve expected that calling analogWriteFreq(50); would just create a 100 Hz signal.
But this was not the case, actually a 50 Hz signal was created but with a wrong duty period. I think the root cause is the function __analogWriteFreq():

Arduino/cores/esp8266/core_esp8266_wiring_pwm.cpp

Lines 35 to 44 in 32323e5

	extern void __analogWriteFreq(uint32_t freq) {
	if (freq < 100) {
	analogFreq = 100;
	} else if (freq > 60000) {
	analogFreq = 60000;
	} else {
	analogFreq = freq;
	}
	_setPWMFreq(freq);
	}

I would suggest the final call should be _setPWMFreq(analogFreq); otherwise the module keeps calculating with the corrected frequency analogFreq but the actual frequency is the maybe illegal requested one.
Side question: why does this module limit the frequency to > 100 Hz when e. g. 50 Hz seems to work??

Additionally I had problems with increasing the resolution - it works fine up to 13 bits with analogWriteResolution(13);, as soon as I set it to 14, 15, or 16 (even with a "legal" frequency) then the duty period is not correct any more. I did not analyze this issue - did anyone else have the same problem or even knows the root cause?

Final question: I realized that when using PWM then loop() is executed with the frequency of the PWM signal - is this the expected behavior? Is there a way to avoid that and get loop() executed as often as possible?

Best regards,
Thomas

[songyx]

the function __analogWriteFreq seems not set the limit to the input seq.
I hava the same question:why not support the 50hz or lower ?it will not cause any problem.

[summer1433]

I think you the lower frequency that you want to create, can write a task do it by yourself

…

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[songyx]

yes I can.I just want to know why there is a limit of >100hz.