3 years, 3 months ago.

Does mbed compiler can program these?

Hi, I have two problems about mbed compiler here. 1. Can I use compiler toset up the CCxIF(image 1, basic on PWM mode of stm32f334xx reference manual)? I want to use for invert my PWM. 2. I use PwmOut function to output PWM as you see as image 2. But the peak time only has 2us as you see as image 2. I also set up other peak time and find that all peak time are only become digit before the decimal point (3.5us to be 3us, 4.3us to be 4us). How can I output the peak time include the digit after decimal point? Please give me answers, thank you. /media/uploads/zeroex123/ask222.jpg

Hi so k, I don't have the answer but if you check the documentation for pwmout https://developer.mbed.org/handbook/PwmOut you see that pulsewidth_us takes an int value. This explains picture 2 I think. Perhaps someone else can help with the rest of the question.

posted by Ian Kilburn 22 Feb 2017

I am sorry that I forget to write that I also use 'int' for pulsewidth_us function and 'float' for pulsewidth function,but they also same as image 2 (to be a value that digit before the decimal point).

posted by so k 23 Feb 2017

Hi so k, the pwmout function has that limitation. The function is limited to int values so your float is truncated. Have you looked at the library FastPWM? https://developer.mbed.org/users/Sissors/code/FastPWM/ You might need to make your own version to support your board. You could also make a change in your new library to set the polarity of the PWM. I think you should be able to use the STM HAL functions for that. I hope this helps.

posted by Ian Kilburn 23 Feb 2017

ok, let go back to question1, I see that there is a 'FastPWM_STM_TIM_PinOut.cpp' in the Device of FastPWM, and I see that there is some code for set PWM to channels. Can I change the codes here to make a invert PWM (like make a invert '!'function here)? Since I only need one channel for PWM inverting. If it is possible, can you tell me that how to change? Thank you.

posted by so k 23 Feb 2017

Hi so k,

To modify the pinout file look at the alternative function of the GPIO pins in the data sheet in table 13. http://www.st.com/content/ccc/resource/technical/document/datasheet/d1/cd/3d/18/a2/2c/4e/d0/DM00097745.pdf/files/DM00097745.pdf/jcr:content/translations/en.DM00097745.pdf

They have the form TIM1_CH1. I have the F030R8 which already works with the library so I can't test this.

Add this to the FastPWM_STM_TIM_PinOut.cpp file

#if defined (TARGET_NUCLEO_F334R8)
__IO uint32_t* getChannel(TIM_TypeDef* pwm, PinName pin) {
    switch (pin) {
        // Channels 1
        case PA_4: case PA_6:  case PB_4: case PB_8: case PB_9: case PB_14: case PC_6: case PB_6: case PB_7:
            return &pwm->CCR1;
        // Channels 2
        case PA_7: case PB_5: case PC_7:
            return &pwm->CCR2;
        // Channels 3
        case PB_0: case PC_8:
            return &pwm->CCR3;
        // Channels 4
        case PC_9:
            return &pwm->CCR4;
    return NULL;

Or something like that. You'll have to check yourself if that works with your board.

As for the polarity I think you need to set the correct bits in the TIMx_CCER register?

I tried this and it seems to be working on my board with PA_6 and PA_7.

Replace this part in the FastPWM_STM_TIM.cpp file

void FastPWM::initFastPWM(void) {
    fast_obj = new fastpwm_struct;
    #if defined(TARGET_STM32F0) || defined (TARGET_STM32F1) || defined (TARGET_STM32L1)
    PWM_CHANNEL = getChannel(PWM_TIMER, _pwm.pin);
    PWM_CHANNEL = (&PWM_TIMER->CCR1 + _pwm.channel - 1); 
    // Depending on the timer and the internal bus it is connected to, each STM timer
    // can have a fixed prescaler from the clock, especially the faster devices.
    // In order not to have to hardcode this in, we use knowledge that mbed lib sets
    // default period to 20ms to reverse engineer the prescaler from this. 
    uint32_t current_hz = SystemCoreClock / (PWM_TIMER->PSC + 1) / (PWM_TIMER->ARR+1);
    PWM_CLK_PRESCALER = (current_hz + 1) / 50;  //50Hz is magic number it should be, +1 is to handle possible rounding errors in mbed setup
    //Sanity check in case a target does something different
    if ( (PWM_CLK_PRESCALER == 0 ) || (PWM_CLK_PRESCALER > 16)) {
        PWM_CLK_PRESCALER = 1;
    PWM_TIMER->CCER =TIM_CCER_CC1P; // invert polarity on channel 1
    PWM_TIMER->CCER |= TIM_CCER_CC1E; //enable channel 1
    PWM_TIMER->CCER |= TIM_CCER_CC2E; //enable channel 2
    bits = 16;
    //Enable PWM period syncing for glitch free result

Hope you can get it working too. Regards Ian

posted by Ian Kilburn 23 Feb 2017

That's ok now,thank you!

posted by so k 24 Feb 2017

1 Answer

3 years, 3 months ago.


You can use the FastPWM https://developer.mbed.org/users/Sissors/code/FastPWM/ library to get non-integer microsecond pulses. If you are only using channel 1 and 2 on STM32 you can directly modify the registers to change the polarity.

add this to the initFastPWM definition

PWM_TIMER->CCER =TIM_CCER_CC1P; // invert polarity on channel 1
    PWM_TIMER->CCER |= TIM_CCER_CC1E; //enable channel 1
    PWM_TIMER->CCER |= TIM_CCER_CC2E; //enable channel 2

Accepted Answer

That's ok now, thank you!

posted by so k 24 Feb 2017