PWM issue with TIMER2

[hathach]

Board: Adafruit WICED Feather https://www.adafruit.com/product/3056
Issue: PWM with PA15 (Timer2 CH1) only start to work after 3-5 minutes.
Solution:
I have spent a few days to follow all the registers and dive into ST manuals to troubleshoot the issue. It turns out to be a very easy fix. As far as I know the EGR_UG bit must be set after setting the Preload to have preload value taking effect immediately. Otherwise, we will need to wait for 2-3 minutes before it starts to work !!!!!!!

Code : Moving Line 161 regs->EGR = TIMER_EGR_UG to right above the timer resume L178.
https://github.com/rogerclarkmelbourne/Arduino_STM32/blob/master/STM32F4/cores/maple/boards.cpp#L161

static void timerDefaultConfig(timer_dev *dev) {
    timer_adv_reg_map *regs = (dev->regs).adv;
    const uint16 full_overflow = 0xFFFF;
    const uint16 half_duty = 0x8FFF;

    timer_init(dev);
    timer_pause(dev);

    regs->CR1 = TIMER_CR1_ARPE;
    regs->PSC = 1;
    regs->SR = 0;
    regs->DIER = 0;
//    regs->EGR = TIMER_EGR_UG; // MOVE FROM HERE

    switch (dev->type) {
    case TIMER_ADVANCED:
        regs->BDTR = TIMER_BDTR_MOE | TIMER_BDTR_LOCK_OFF;
        // fall-through
    case TIMER_GENERAL:
        timer_set_reload(dev, full_overflow);
        for (int channel = 1; channel <= 4; channel++) {
            timer_set_compare(dev, channel, half_duty);
            timer_oc_set_mode(dev, channel, TIMER_OC_MODE_PWM_1, TIMER_OC_PE);
        }
        // fall-through
    case TIMER_BASIC:
        break;
    }

    // UG must be placed after reload to take affect
    regs->EGR = TIMER_EGR_UG; // TO THIS LINE
    timer_resume(dev);
}

[rogerclarkmelbourne]

Thanks

I will see is @martinayotte has time to test for me on his F4 hardware

[ddrown]

I tried this on my STM32F4 discovery board and can confirm the fix.

Test code:

int led = PA15;
int signalpin = PC11;
int brightness = 0;

void setup() {
  pinMode(led, PWM);
  gpio_set_af_mode(GPIOA,  15, 1); // we should probably do this in the pinMode code
  pinMode(signalpin, OUTPUT);
}

void loop() {
  digitalWrite(signalpin, HIGH);
  analogWrite(led, brightness);
  if(brightness == 0) {
    brightness = 32768;
  } else {
    brightness = 0;
  }

  delay(1);
  digitalWrite(signalpin, LOW);
  delay(29);
}

Before CH1/Yellow = PA15, CH2/Blue = PC11:

After:

The PWM output does eventually show up without the change.

[rogerclarkmelbourne]

Thanks Dan

I'll do a merge straight on Github

Edit

Oops

I've realized this is not a PR.

Can you or the OP do this as a PR ?

[rogerclarkmelbourne]

Any chance of a PR for this ?

[martinayotte]

Hi Roger,
Since I've never tried any PWM on F4, if it is working for @ddrown, I will agree that your can merge almost blindly, I will give it a try later when the "famous time ingredient" is coming back in stock :-)