Stop PWM output after N steps

[harry_rostovtsev]

Posted on August 27, 2012 at 20:01

Is there a way to tell a TIMer on STM32 chips to do some number of steps and automatically stop after finished (and give an interrupt)?  I can do it now with a counter in the ISR but a few pulses slip out before I can shutdown the PWM output or the timer.

[harry_rostovtsev]

Posted on August 27, 2012 at 21:58

Here's my current code:

uint16_t number_of_steps;
int main(void) {
NVIC_InitTypeDef nvic_init;
NVIC_ClearPendingIRQ(TIM8_UP_TIM13_IRQn);
nvic_init.NVIC_IRQChannel = TIM8_UP_TIM13_IRQn;
nvic_init.NVIC_IRQChannelPreemptionPriority = 0;
nvic_init.NVIC_IRQChannelSubPriority = 0;
nvic_init.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&nvic_init);/* enables the device and sets interrupt priority */
NVIC_ClearPendingIRQ(TIM8_CC_IRQn);
nvic_init.NVIC_IRQChannel = TIM8_CC_IRQn;
nvic_init.NVIC_IRQChannelPreemptionPriority = 1;
nvic_init.NVIC_IRQChannelSubPriority = 1;
nvic_init.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&nvic_init);/* enables the device and sets interrupt priority */
/* set priorities of all interrupts in the system... */
NVIC_SetPriority(SysTick_IRQn, 1);
NVIC_SetPriority(TIM8_UP_TIM13_IRQn, 2);
NVIC_SetPriority(TIM8_CC_IRQn, 3);
GPIO_InitTypeDef GPIO_InitStructure;
/* ENABLE GPIOC clock enable */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE);
/* GPIOC Configuration:TIM8 Channel3 in Output */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_DOWN;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_Init(GPIOC, &GPIO_InitStructure);
/* Connect TIM8 pins to AF */
GPIO_PinAFConfig(GPIOC, GPIO_PinSource8, GPIO_AF_TIM8);
/* Compute the value to be set in ARR register to generate signal frequency at 57 Khz */
TimerPeriod = (SystemCoreClock / 2000 ) - 1;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
/* TIM8 clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM8, ENABLE);
/* how many steps are we going */
number_of_steps = 20;
/* Time base configuration */
uint16_t Period = 1000000 / 2000; // 2 KHz for 1MHz prescaled
TIM_TimeBaseStructure.TIM_Period = Period - 1; // 1 MHz down to 1 KHz (1 ms)
TIM_TimeBaseStructure.TIM_Prescaler = 120 - 1; // 120 MHz Clock down to 1 MHz (adjust per your clock)
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM8, &TIM_TimeBaseStructure);
/* PWM Mode configuration: Channel3 */
TIM_OCInitStructure.TIM_Pulse = Period / 2;
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
/* Output Compare PWM1 Mode configuration: Channelc Pc.08 */
TIM_OC3Init(TIM8, &TIM_OCInitStructure);
TIM_OC3PreloadConfig(TIM8, TIM_OCPreload_Enable);
/* TIM8 enable counter */
TIM_Cmd(TIM8, ENABLE);
TIM_ITConfig(TIM8,TIM_IT_Update, ENABLE);
TIM_CtrlPWMOutputs(TIM8, ENABLE);
while (1)
{
}
}
void TIM8_UP_TIM13_IRQHandler(void) {
if (number_of_steps == current_step) {
TIM8->CCR3 = 0;
TIM8->CR1 &= (uint16_t)~TIM_CR1_CEN; // this is same as TIM_Cmd(TIM8, DISABLE);
TIM_ITConfig(TIM8,TIM_IT_Update, DISABLE);
current_step = 1;
}
current_step++;
// If this is uncommented, I have a few extra pulses that sneak out
//printf(''TIM8 update int
''); 
// If this is commented out, I only get 1 or 2 pulses, as if my ISR goes by to quickly
if (TIM_GetITStatus(TIM8, TIM_IT_Update) != RESET) {
TIM_ClearITPendingBit(TIM8, TIM_IT_Update);
}
}

If you look in the interrupt handler, you can see my comment specify the problems. Basically, I don't think I'm using the right kind of interrupt (though I got similar behavior when I used the CCR interrupt).

[rod_gilchrist]

Posted on January 29, 2013 at 15:59

Yes. (I am reading your question as that you wish to emit a specified number of PWM pulses.)

The STM32 documentation implies that a timer is either  in Master mode (wherein it can output a signal on an internal trigger line) or Slave mode (wherein it can be triggered from things like an internal trigger line). The truth is that it can be both a Master and a Slave at the same time. 

I use this  understanding to emit a specified number of pulses by connecting two timers 'back to back' and I use the repetition counter on an advanced counter to specify the number of pulses.

Specifically, I put Timer 1 (which has a repetition counter) in PWM mode configured to generate pulses with the timing I want. I then configure its slave controller to be gated by Timer 4 on internal trigger 3 (any of timers 2, 3 or 4 would work, but timer 5 won't due to internal trigger connectivity). I also set Timer 1's master controller to emit an update event on its trigger output.

I then configure Timer 4 in one pulse mode with a wide pulse (longer than 256 Timer 1 pulses) with its master controller outputting a compare output channel on 'trigger out' to gate Timer 1 and its slave controller set to reset Timer 4 based on the signal on internal trigger 0 (i.e. the update event from Timer 1, which only occurs after 'n' PWM pulses, depending on the value set in the Timer 1 repetition counter (which can be 1 to 256)).

I haven't tried it, but I imagine the Timer 1 update would generate an interrupt in the normal way if desired, but with this configuration the pulse count is not dependent on interrupt speed. 

Hope this helps.

[rod_gilchrist]

Posted on January 30, 2013 at 15:52

Stop PWM output after N steps

Is there a way to tell a TIMer on STM32 chips to do some number of steps and automatically stop after finished (and give an interrupt)?  I can do it now with a counter in the ISR but a few pulses slip out before I can shutdown the PWM output or the timer.

My previous post describes how to do this.

One point that I didn't make is that you do have to trigger an update event (i.e. set the update event bit in the Timer 1 EGR register) after you set the pulse count in the repetition register. The update event is required to load the repetition count into the actual down counter.

I do this just before setting the enable bits on the two timers.

[Amel NASRI]

Posted on January 31, 2013 at 14:18

I guess the break input feature will be helpfull in your case. Did you tried it?

ST.MCU

[barry]

Posted on January 27, 2015 at 16:26

Rod,

Have you actually gotten the code to work?

If so, could you post the code.  Is timer 8 completely identical to timer 1.

Thanks

Barry

[Tesla DeLorean]

Posted on January 27, 2015 at 16:57

Is timer 8 completely identical to timer 1.

They are both ''advanced'' timers, so you'd need to initialize the repetition count in the timebase, the N output settings in the channels, and enable the PWM output(input)

[barry]

Posted on January 28, 2015 at 19:51

Thanks Clive,

Another question 

I am currently using timer 3(to generate aninterrupt once every  4 seconds)  to control timer 4 (I have hardwareconnected to PE12), but without a master slave connection.  This is not workingvery well to to generate an exact number  (200) of pulses.  It isclose but over a long time frame the stepper motor will drift off the correctstarting point.

Do you think I can use timer 8 and its repetitioncounter as the master to control timer 4 PWM pulses so I get an exact number ofpulses for a stepper motor?

The example in this thread seems to use theadvanced timer to generate the PWM pulses.

Are there any examples in the various STdistributions?

If this can't work, can I use timer 4 in a onepulse mode (and handle 200 interrupts)? The exact timing of the stepper motorpulses is not critical.

Thanks

Barry

[Tesla DeLorean]

Posted on January 28, 2015 at 21:58

// STM32 FIVE 20 KHz PULSES at 50 Hz (20ms Intervals) (TIM1 CH1 PA.08) STM32F4 Discovery - [e-mail]
#include ''stm32f4_discovery.h''
/**************************************************************************************/
void RCC_Configuration(void)
{
/* --------------------------- System Clocks Configuration -----------------*/
/* TIM1 clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE);
/* TIM3 clock enable */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
/* GPIOA clock enable */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
}
/**************************************************************************************/
void GPIO_Configuration(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
/*-------------------------- GPIO Configuration ----------------------------*/
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* Connect TIM1 pins to AF */
GPIO_PinAFConfig(GPIOA, GPIO_PinSource8, GPIO_AF_TIM1);
}
/**************************************************************************************/
void TIM1_Configuration(void)
{
TIM_OCInitTypeDef TIM_OCInitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
uint16_t Period;
Period = 1000000 / 20000; // 20 KHz from 1MHz prescaled
/* Time base configuration */
TIM_TimeBaseStructure.TIM_Prescaler = (SystemCoreClock / 1000000) - 1; // Get clock to 1 MHz on STM32F2/F4
TIM_TimeBaseStructure.TIM_Period = Period - 1;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_RepetitionCounter = 5 - 1; // Five Pulses per trigger
TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
/* Enable TIM1 Preload register on ARR */
TIM_ARRPreloadConfig(TIM1, ENABLE);
/* TIM PWM1 Mode configuration */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = Period / 2; // 50%
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
/* Output Compare PWM1 Mode configuration: Channel1 PA.08 */
TIM_OC1Init(TIM1, &TIM_OCInitStructure);
TIM_OC1PreloadConfig(TIM1, TIM_OCPreload_Enable);
/* One Pulse Mode selection */
TIM_SelectOnePulseMode(TIM1, TIM_OPMode_Single);
/* Input Trigger selection */
TIM_SelectInputTrigger(TIM1, TIM_TS_ITR2); // Slave TIM1, Trigger TIM3 (TS=2)
/* Slave Mode selection: Trigger Mode */
TIM_SelectSlaveMode(TIM1, TIM_SlaveMode_Trigger);
/* TIM1 Main Output Enable */
TIM_CtrlPWMOutputs(TIM1, ENABLE);
/* TIM1 enable counter */
TIM_Cmd(TIM1, ENABLE);
}
/**************************************************************************************/
void TIM3_Configuration(void)
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
uint16_t Period;
Period = 1000000 / 50; // 50 Hz from 1MHz prescaled
/* Time base configuration */
TIM_TimeBaseStructure.TIM_Prescaler = ((SystemCoreClock / 2) / 1000000) - 1; // Get clock to 1 MHz on STM32F2/F4
TIM_TimeBaseStructure.TIM_Period = Period - 1;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
/* Trigger of TIM3 Update into TIM1 Slave */
TIM_SelectOutputTrigger(TIM3, TIM_TRGOSource_Update);
/* TIM3 enable counter */
TIM_Cmd(TIM3, ENABLE);
}
/**************************************************************************************/
int main(void)
{
RCC_Configuration();
GPIO_Configuration();
TIM1_Configuration();
TIM3_Configuration();
while(1); // Don't want to exit
}
/**************************************************************************************/
#ifdef USE_FULL_ASSERT
/**
* @brief Reports the name of the source file and the source line number
* where the assert_param error has occurred.
* @param file: pointer to the source file name
* @param line: assert_param error line source number
* @retval None
*/
void assert_failed(uint8_t* file, uint32_t line)
{
/* User can add his own implementation to report the file name and line number,
ex: printf(''Wrong parameters value: file %s on line %d

'', file, line) */
/* Infinite loop */
while (1)
{
}
}
#endif

[barry]

Posted on January 28, 2015 at 23:22

Clive,

I'll give it a try.

Thanks

Barry

[barry]

Posted on February 08, 2015 at 17:46

Thanks again Clive.

One question,  I can't figure out what one instruction will start the pulse sequence.

I don't want to start the pulses immediately at initialization  time and I want to repeat the sequence over and over.

The code shown below works, but I think I could clean it up if I understood the timers as well as you.

I am using the update interrupt to get additional cycles of 200 pulses

 /* Enable the TIM8 gloabal Interrupt */

  NVIC_InitStructure.NVIC_IRQChannel = TIM8_UP_TIM13_IRQn;

  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;

  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;

  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

  NVIC_Init(&NVIC_InitStructure);

 /* TIM Interrupts enable */

  TIM_ITConfig(TIM8, TIM_IT_Update , ENABLE);

  

................

//Interrupt Handler

void   TIM8_UP_TIM13_IRQHandler(void)

{

  if (TIM_GetITStatus(TIM8, TIM_IT_Update) != RESET)

  {

    TIM_ClearITPendingBit(TIM8, TIM_IT_Update);

    tim8_counter--;

    if ( tim8_counter != 0)

    {

         TIM8_Restart();

    }

  }

}

 

  

 

void TIM8_Restart(void)  // This seems to work

{

  /* TIM8 Main Output Enable */

  TIM_CtrlPWMOutputs(TIM8, ENABLE);

   /* TIM8 enable counter */

  TIM_Cmd(TIM8, ENABLE);

}

 

//This is what I do the first time and when I want to send another series of 200 pulses

// Some of these instructions were removed from the init code you posted

     tim8_counter = TIM8_INTERRUPTS;

    TIM_CtrlPWMOutputs(TIM8, ENABLE);

    TIM_Cmd(TIM8, ENABLE);

    TIM_Cmd(TIM3, ENABLE);

    TIM8_Restart();

Any ideas on what is actually turn the pulses off and on?

Thanks

Barry