STM32F4 configure TIMER2 for 1microsec interrupt

[hariprasad]

Posted on November 10, 2014 at 15:14

Hi

I want to generate a timer interrupt after every 1micoseconds. I am using TIMER2 for this purpose.So I took a code from one site and modified for my purpose. But the issue is I cant get an interrupt of 1microsecond.To ensure this I toggled a gpio in the ISR and verified the frequency on DSO and it was found to be 806Khz. Is there anything that I'm doing wrong in the code? void TIM2_IRQHandler(void) {   if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET)   {         count++;       TIM_ClearITPendingBit(TIM2, TIM_IT_Update);         flag_for_state_machine=1;         if(count%2 == 0)             GPIO_ResetBits(GPIOD, GPIO_Pin_12);         else             GPIO_SetBits(GPIOD, GPIO_Pin_12);   } } void configure_d1_d2_d3(void) {         /* Enable the GPIO_LED Clock */     RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);     GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12;     GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;     GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;     GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_DOWN;     GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;     GPIO_Init(GPIOD, &GPIO_InitStructure); } void INTTIM_Config(void) {   NVIC_InitTypeDef NVIC_InitStructure;   /* Enable the TIM2 gloabal Interrupt */   NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;   NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;   NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;   NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;   NVIC_Init(&NVIC_InitStructure);   /* TIM2 clock enable */   RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);       /* Time base configuration */   TIM_TimeBaseStructure.TIM_Period = 1;   TIM_TimeBaseStructure.TIM_Prescaler = 0;   TIM_TimeBaseStructure.TIM_ClockDivision = 0;   TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;   TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);   /* TIM IT enable */   TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);   /* TIM2 enable counter */   TIM_Cmd(TIM2, ENABLE); } int main(void) {             configure_d1_d2_d3();         INTTIM_Config();         while(1);         } #discovery #stm32f4 #timers

[Tesla DeLorean]

Posted on November 10, 2014 at 15:47

Interrupting at 1 MHz is ridiculously fast, think a bit harder about a better way to solve whatever problem you are trying to solve.

TIM_TimeBaseStructure.TIM_Period = 1; // Like 84 MHz / 2? WTF? TIM_TimeBaseStructure.TIM_Prescaler = 0;

[Tesla DeLorean]

Posted on November 10, 2014 at 15:51

TIM_TimeBaseStructure.TIM_Period = ((SystemCoreClock / 2) / 1000000) - 1;  // 1 MHz (1us)

Toggling will HALF the measured frequency. So if the interrupt occurs at 1 MHz (1 us) the pin frequency will be 500 KHz

[stm322399]

Posted on November 10, 2014 at 15:59

IMHO, you should ask yourself how to execute the following under 1us:

void TIM2_IRQHandler(void)
{
if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET)
{
count++;
TIM_ClearITPendingBit(TIM2, TIM_IT_Update);
flag_for_state_machine=1;
if(count%2 == 0)
GPIO_ResetBits(GPIOD, GPIO_Pin_12);
else
GPIO_SetBits(GPIOD, GPIO_Pin_12);
}
}

What about having a look at assembly code ? Then try to follow the flow or count instructions (beware 1 instruction may require more than one cycle). Clive is right, there are very few use case that requires to go at that rate. What do you try to achieve ? Maybe it could be done in an other way (DMA ?).

[hariprasad]

Posted on November 18, 2014 at 05:37

Hi Clive,

Thanks for the reply, that worked If I want to generate interrupt at 2 Mhz (0.5microsec) How should I modify the above program?

[Tesla DeLorean]

Posted on November 18, 2014 at 15:09

If this wasn't evident from the previous example:

TIM_TimeBaseStructure.TIM_Period = ((SystemCoreClock / 2) / 2000000) - 1;  // 2 MHz You should really let the hardware do the toggling at these rates, it's not a viable rate to interrupt at, and at some point you will saturate the processor.