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earlephilhower / arduino-pico

Raspberry Pi Pico Arduino core, for all RP2040 and RP2350 boards
GNU Lesser General Public License v2.1
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Difference between the documentation and the code for analogWriteFreq #2334

Closed jlbirccyn closed 3 weeks ago

jlbirccyn commented 3 weeks ago

Hello.

The documentation gives a maximum frequency of 1MHz for PWMs, but in the analogWriteFreq function, the test is performed with a value of 10MHz.

Documentation : https://arduino-pico.readthedocs.io/en/latest/analog.html#void-analogwritefreq-uint32-t-freq

Code : https://github.com/earlephilhower/arduino-pico/blob/bd64b97a20dd5da484572788fd76f92cd6491768/cores/rp2040/wiring_analog.cpp#L48

Best regards

earlephilhower commented 3 weeks ago

PWM is basically a counter with a configurable reset value and a clock. Physically, yes, you can run 10MHz. But at that PWM period with a 133MHZ PWM clock you only can count to 133M/10M = ~13, or less than 4 bits (log2(13)) of resolution. Not too useful.

A much more useful PWM frequency would be 1M, as specified in the docs. Then you have slightly more than 7 bits of resolution to work with.

So, if you really want 10M, go for it, but the docs are specifying a much more reasonable config.