Changing PWM (analogWrite) resolution

[mcer12]

Is there any way to change the PWM resolution / range for analogWrite? The STM32s are capable of 16bit PWM but I didn't find any information of how to change that in Arduino IDE.
If there is an example of this that I missed, please post a link, I will close the issue asap.

[fpistm]

Hi @mcer12
See https://www.arduino.cc/reference/en/language/functions/zero-due-mkr-family/analogwriteresolution/
by default it is 8 bits.
So the range of the value used as argument of analogWrite is 0-1023 but it is converted to 12 bits internally thanks:

Arduino_Core_STM32/cores/arduino/wiring_analog.c

Line 118 in f2ef8f2

ulValue = mapResolution(ulValue, _writeResolution, PWM_RESOLUTION);

Where:

Arduino_Core_STM32/cores/arduino/pins_arduino.h

Lines 307 to 309 in f2ef8f2

	#ifndef PWM_FREQUENCY
	#define PWM_FREQUENCY 1000
	#endif

The internal PWM_RESOLUTION can also be redefined using the build_opt.h:
https://github.com/stm32duino/wiki/wiki/Customize-build-options-using-build_opt.h

You can also change the PWM freq (note that it will be more accurate in the 1.7.0 as it will use HardwareTimer library):
https://github.com/stm32duino/wiki/wiki/API#frequency

[mcer12]

Great thank you for this! It didn't even cross my mind to try the Due page.

[mcer12]

So I found out that the PWM_RESOLUTION is in fact 8bit and not 12bit by default. I used analogWriteResolution(12);
which allowed me to use 12bit values but those were converted back to 8bit. I got around that by setting
PWM_RESOLUTION 12
PWM_MAX_DUTY_CYCLE 4095
in pins_arduino.h

[fpistm]

In the next release this will be 12 per defaut. In tbe 1.6.1 it is 8 bits.

[fpistm]

avoid to edit core files, and as said:

The internal PWM_RESOLUTION can also be redefined using the build_opt.h:
https://github.com/stm32duino/wiki/wiki/Customize-build-options-using-build_opt.h

This allow to change core behavior at sketch level.