Can't produce 20 ms PWM for servo

[nyanlynnhtet07]

Posted on October 25, 2016 at 15:54

Hi. I am quite new to STM32. 

I would like to produce 20ms square PWM with adjustable duty cycle for controlling 2 servo position. MCU = stm32f103ret6  Using GNU ARM toolchain on Eclipse cdt. Use Timer5 Ch1,2 (PA0, PA1 for servo signal). Here is the code I write so far. // For GPIO Initializationvoid GPIO_Init_Mode_50MHz(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin, GPIOMode_TypeDef mode) { GPIO_InitTypeDef GPIO_InitStructure; GPIO_InitStructure.GPIO_Pin = GPIO_Pin; GPIO_InitStructure.GPIO_Mode = mode; GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz; GPIO_Init(GPIOx, &GPIO_InitStructure);}void InitTimer5_servoPWM(bool bCH1, bool bCH2){    TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;    TIM_OCInitTypeDef  TIM_OCInitStructure;ss /* TIM5 clock enable */    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM5, ENABLE);     /* Time base configuration */    TIM_TimeBaseStructure.TIM_Prescaler = 63;    TIM_TimeBaseStructure.TIM_ClockDivision = 0;    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;    TIM_TimeBaseStructure.TIM_Period = 20000; // period in usec    TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;    TIM_TimeBaseInit(TIM5, &TIM_TimeBaseStructure);    /* Output Compare Active Mode configuration: Channel1 */    TIM_OCStructInit(&TIM_OCInitStructure);    TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;    TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;    TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;    RCC_AHBPeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE); //Timer5_CH1(PA0) Timer5_CH2(PA1)    if (bCH1) {    GPIO_Init_Mode_50MHz(GPIOA, GPIO_Pin_0, GPIO_Mode_AF_PP);    /* Output Compare Timing Mode configuration: Channel1 */    TIM_OC1Init(TIM5, &TIM_OCInitStructure);    TIM_OC1PreloadConfig(TIM5, TIM_OCPreload_Enable);    TIM5->CCR1 = 0;    }    if (bCH2) {    GPIO_Init_Mode_50MHz(GPIOA, GPIO_Pin_1, GPIO_Mode_AF_PP);        /* Output Compare Timing Mode configuration: Channel1 */    TIM_OC2Init(TIM5, &TIM_OCInitStructure);    TIM_OC2PreloadConfig(TIM5, TIM_OCPreload_Enable);    TIM5->CCR2 = 0;    }    TIM_ARRPreloadConfig(TIM5, ENABLE);    // output enable for TIM5 only    TIM_CtrlPWMOutputs(TIM5, ENABLE);    TIM_Cmd(TIM5, ENABLE); }  // For changing dutycycle void SetTimer5PWM(int16_t ch, int16_t pwm) { switch(ch) { case 1 : TIM5->CCR1 = pwm; break; case 2 : TIM5->CCR2 = pwm; break; }} #stm32f103-pwm #stm32f103-pwm #!adxl345

[waclawek.jan]

Posted on October 25, 2016 at 16:27

Timer runs? (verify e.g. looking at TIM_CNT in debugger)

JW

[Tesla DeLorean]

Posted on October 25, 2016 at 16:30

If you are not getting 20ms period what are you getting? What aspect of this is ''not working'' ?

I'd recommend not using the 50MHz slew-rate setting on a signal below 1MHz

[michaelc.barton9]

Posted on October 25, 2016 at 16:48

you'll need these lines where you're configuring the GPIO:

GPIO_PinAFConfig(GPIOA, GPIO_PinSource0, GPIO_AF_??); GPIO_PinAFConfig(GPIOA, GPIO_PinSource1, GPIO_AF_??); I'm not sure exactly which GPIO_AF_* number you'll need to use as the help docs are a little obtuse for the STM32F1* series :(

[Tesla DeLorean]

Posted on October 25, 2016 at 16:55

The F1 series doesn't support GPIO_PinAFConfig as the AF options are peripheral rather than pin mapped.

[michaelc.barton9]

Posted on October 25, 2016 at 17:12

oops - yes, was somehow looking at F0 :(

[nyanlynnhtet07]

Posted on October 26, 2016 at 03:36

CNT is 0. It doesn't increase. 

When I check with scope, it shows a funny wave that changes between 40k-250kHz and sometimes 1MHz. Is there a need to do something like pin map for Timer5 and PA0, PA1? The address of TIM5 is not available in my GPIO firmware library for mapping. 

[waclawek.jan]

Posted on October 26, 2016 at 09:20

Then you need to enable it by setting CEN bit in TIMx_CR1. I don't use any of the ''libraries'' but there must be a function or macro for this, refer to your ''library'''s manual.

JW

[Tesla DeLorean]

Posted on October 26, 2016 at 15:15

The TIM5_CH1/2 are default mappings for PA0/PA1 but there are several other peripherals sharing this, and they might need to be remapped if they conflict.

You'd need to check the data-sheet for the specific F1 part to see which TIMx it supports. Generally if the TIM is not present all TIMx->registers will be zero, and the clock enable bit for the APB will be stuck-at-zero. I've posted numerous servo examples, review older forum posts. Consider also what else on the board is connected to or using these pins.