STM32 timer --- master-slave mode triggers PWM phase shift

In this article, the trigger mode is used instead of the gate mode.

code show as below:

void TIM3_PWMShiftInit(void)  

{  

    TIM_TimeBaseInitTypeDef  TIM_TimeBaseInitStruct;  

    GPIO_InitTypeDef  GPIO_InitStruct;  

    TIM_OCInitTypeDef TIM_OCInitStruct;  

    /**********************TIM3 GPIO configuration****************************/  

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB|RCC_APB2Periph_GPIOA, ENABLE);  

    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF_PP;  

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_0|GPIO_Pin_1|GPIO_Pin_13;  

    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;  

    GPIO_Init(GPIOB,&GPIO_InitStruct);  

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_8; 

    GPIO_Init(GPIOA,&GPIO_InitStruct);  

    /**********************Initialize TimBase structure****************************/  

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE); //Turn on TIM clock

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1,ENABLE);

    TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1; //Timer does not divide frequency

    TIM_TimeBaseInitStruct.TIM_CounterMode   = TIM_CounterMode_Up;  

    TIM_TimeBaseInitStruct.TIM_Period = 1799; //Frequency = 72000000/PSC/(ARR+1) = 40KHz 

    TIM_TimeBaseInitStruct.TIM_Prescaler = 0;       

    TIM_TimeBaseInit(TIM3, &TIM_TimeBaseInitStruct);  

    TIM_TimeBaseInit(TIM1, &TIM_TimeBaseInitStruct);  

    /**********************Initialize TIM3 OC structure****************************/  

    TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM2;  

    TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_Low;  

    TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;  

    TIM_OCInitStruct.TIM_Pulse = 600; //TIM3 CH3 duty cycle: 600/(ARR+1)=33.3%

    TIM_OC3Init(TIM3,&TIM_OCInitStruct);  

    //TIM1 CH1pwm output configuration         

    TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM2;  

    TIM_OCInitStruct.TIM_Pulse=600; //TIM1 CH1 duty cycle: 600/(ARR+1)=33.3%

    TIM_OCInitStruct.TIM_OCPolarity=TIM_OCPolarity_Low; //Set output polarity              

    TIM_OCInitStruct.TIM_OutputNState=TIM_OutputNState_Disable; //Disable complementary terminal output. Output polarity cannot be adjusted without this statement.                         

    TIM_OC1Init(TIM1,&TIM_OCInitStruct);            

    /**************************Configure phase shift trigger**************************/

    TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM2; //PWM2 and Toggle modes can trigger phase shift, other modes cannot

    TIM_OCInitStruct.TIM_Pulse = 600-2; //It takes about 2 timer cycles to trigger, phase shift: 360*600/(ARR+2)= 120 degrees

    TIM_OC2Init(TIM1,&TIM_OCInitStruct); //Need CH2 rising edge trigger. If the phase shift cannot be triggered, please change the output polarity of CH2.

    /**************************Configure master-slave mode****************************/

    TIM_SelectOutputTrigger(TIM1, TIM_TRGOSource_OC2Ref); //TIM1 OC2 triggers slave timer

    TIM_SelectMasterSlaveMode(TIM1, TIM_MasterSlaveMode_Enable); 

    TIM_SelectInputTrigger(TIM3, TIM_TS_ITR0); //ITRO trigger

    TIM_SelectSlaveMode(TIM3, TIM_SlaveMode_Trigger);   

    TIM_Cmd(TIM1, ENABLE);

    TIM_CtrlPWMOutputs(TIM1, ENABLE); //Advanced timer pwm output enable, be sure to turn it on

The oscilloscope displays the following waveform:

CH1: TIM1 CH1

CH2: TIM3 CH3

Figure 1 shows that the frequency and duty cycle are correct, and combined with Figure 2, it can be seen that the phase shift degree is correct.

After observing the output of the two timers at different frequencies and duty cycles, it was found that the phase shift had an error of about 25ns, so two timer cycle corrections were performed during initialization.

The oscilloscope is zoomed in to 25ns, and it can be seen that after correction by 600-2,2 timer cycles (the timer does not divide the frequency), the phase shift has basically no offset.