How are the PWM signals generated by an Arduino Uno?

Backflip · May 23, 2025, 1:55pm

I have noticed the video on this link:
https://docs.simplefoc.com/arduino_simplefoc_shield_showcase

As far as I understand this video, a simple form of FOC is utilized by the controls from an Arduino Uno. I know the inner hardware of the Atmega 328P chip quite well, but I cannot figure out how this MPU is able to provide the PWM-signals for three phases (three half bridges). I think that the driver board receives all three PWM signals from the MPU. Are timer1 and timer2 synchronized to do this? I think that timer1 can only provide two PWM signals (not three as in many other MPUs).

I tried to look a bit into the libraries, but I did not find the low-level code that sets the timers.

How are the timers of this MPU utilized here to provide the PWM-signals?

Are the PWM-frequency fixed to be above 31.25 kHz (=16.000 kHz/512)?

runger · May 23, 2025, 4:48pm

Hi @Backflip ,

The low level driver code for 328P is here: Arduino-FOC/src/drivers/hardware_specific/atmega/atmega328_mcu.cpp at master · simplefoc/Arduino-FOC · GitHub

Yes, it syncs the timers and yes it uses 32kHz…

dekutree64 · May 23, 2025, 4:51pm

Yep, it uses multiple timers. The frequency is clamped to either 32kHz or 4kHz due to limited prescaler options. The code is in the drivers/hardware_specific folder:

github.com/simplefoc/Arduino-FOC

src/drivers/hardware_specific/atmega/atmega328_mcu.cpp

master

#include "../../hardware_api.h"

#if defined(__AVR_ATmega328P__) || defined(__AVR_ATmega168__) || defined(__AVR_ATmega328PB__)

#pragma message("")
#pragma message("SimpleFOC: compiling for Arduino/ATmega328 ATmega168 ATmega328PB")
#pragma message("")

#define _PWM_FREQUENCY 32000
#define _PWM_FREQUENCY_MAX 32000
#define _PWM_FREQUENCY_MIN 4000

// set pwm frequency to 32KHz
void _pinHighFrequency(const int pin, const long frequency){
  bool high_fq = false;
  // set 32kHz frequency if requested freq is higher than the middle of the range (14kHz)
  // else set the 4kHz
  if(frequency >= 0.5*(_PWM_FREQUENCY_MAX-_PWM_FREQUENCY_MIN))  high_fq=true; 
  //  High PWM frequency
  //  https://www.arxterra.com/9-atmega328p-timers/

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Backflip · May 23, 2025, 6:45pm

Thank you for your replies. My guess about how the timers needed to be used was right then. There is not much flexibility in PWM-frequency with this MPU.

It is nice to know how to find the code used as well.