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.

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).

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.

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.

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.

#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;
}
#endif 

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.

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);
    #else
    PWM_CHANNEL = (&PWM_TIMER->CCR1 + _pwm.channel - 1); 
    #endif
    
    // 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
    PWM_TIMER->CR1 |= TIM_CR1_ARPE;
}

Hope you can get it working too. Regards Ian

That's ok now,thank you!