Calling analogWrite multiple times causes glitches in PWM signal

[ktand]

Describe the bug
Calling analogWrite multiple times causes glitches in PWM signal

To Reproduce
#include <Arduino.h>

void setup() {
pinMode(PC_6, OUTPUT);
}

void loop() {
analogWrite(PC_6, 128);
delayMicroseconds(50);
}

Expected behavior
The PWM signal should be glitch-free if analogWrite is called repeatedly with the same value. When PWM has been set up for the selected pin the next call to analogWrite should just update the PWM duty cycle. Now it appears that it restarts the PWM signal.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Windows 10
• PlatformIO: ST STM32 6.0.0
• STM32 core version: 1.7.0

Board (please complete the following information):

• Name: armed_v1

Additional context
I'm using STM32 core version 1.7.0 as a part of PlatformIO-ststm32 6.0.0. I have checked the code and the behaviour should be the same in 1.8.0.

[ABOSTM]

Hi @ktand ,

First thee are some issues in your sketch:

1. pinMode(PC_6, OUTPUT);
   this function call is useless because analogWrite() will do the GPIO configuration
2. pinMode() and analogWrite() API accept pin number (PC6) but not pin name (PC_6)

Then, let's discuss the glitch:
with analogWrite() there is a complete reconfiguration of GPIO and HardwareTimer, thus there are intermediate steps where output is deactivated (corresponding to the glitch) and so, with this API, glitch is inevitable.

It is still possible to get ride of glitch by controlling directly HardwareTimer (see below).
For details about Hardware timer:

• See wiki: https://github.com/stm32duino/wiki/wiki/HardwareTimer-library
• See examples of HardwareTimer usage:
  https://github.com/stm32duino/STM32Examples/tree/master/examples/Peripherals/HardwareTimer

#include <Arduino.h>

#define pin PC6

uint32_t channel;
HardwareTimer *MyTim;

void setup() {
  TIM_TypeDef *Instance = (TIM_TypeDef *)pinmap_peripheral(digitalPinToPinName(pin), PinMap_PWM);
  channel = STM_PIN_CHANNEL(pinmap_function(digitalPinToPinName(pin), PinMap_PWM));

  MyTim = new HardwareTimer(Instance);
  MyTim->setPWM(channel, pin, 10000, 50); // 10k Hz 50% dutycycle
}

void loop() {
  MyTim->setCaptureCompare(channel, 50, PERCENT_COMPARE_FORMAT);
  delayMicroseconds(50);
}

[ktand]

Regarding PC_6 vs PC6, my mistake when I created the sample, sorry.

Regarding the glitch. If PWM is already started on the pin, why can't the core just reconfigure the duty cycle? I'm sure the workaround will be fine (thanks for the example) but in this case the analogWrite is called by code supporting many platforms (Marlin 3D printer F/W).

[ABOSTM]

Hi @ktand,
I understand your point and I propose a PR to provide a new API and use it in case of analogWrite.
See: #941