configure a general purpose TIMx (x=2,3,4) same as Systick on STM32F103B

[slimbahri]

Posted on March 12, 2010 at 10:33

configure a general purpose TIMx (x=2,3,4) same as Systick on STM32F103B

[Tesla DeLorean]

Posted on May 17, 2011 at 13:43

#define CPUCLOCK (36.0) // CPU Clock MHz

{

  int i;

  for(i=0; i<10; i++)

  {

    u32 a, b;

    do

    {

      a = SystemTick; // 1ms counter off SYSTICK interrupt

      b = SystemTick;

    } while(a == b); // Sychronize on SYSTICK

    STOPWATCH_START

    Sleep(10); // 10ms delay

    STOPWATCH_STOP

    printf(''%10d cycles, %7.4lf ms\n'',cyc[1],((1.0 / (CPUCLOCK * 1000.0)) * (double)cyc[1])); // 36 MHz clock, milliseconds from cycles

  }

}

    360091 cycles, 10.0025 ms

    360091 cycles, 10.0025 ms

    360089 cycles, 10.0025 ms

    360089 cycles, 10.0025 ms

    360089 cycles, 10.0025 ms

    360091 cycles, 10.0025 ms

    360175 cycles, 10.0049 ms

    360089 cycles, 10.0025 ms

    360177 cycles, 10.0049 ms

    360177 cycles, 10.0049 ms

[Tomas DRESLER]

Posted on May 17, 2011 at 13:43

One more argument FOR SysTick:

reading TIMx through APB brings jitter and delay in range (1+ratio) AHB cycles due to resynchronization between APB and AHB in the bridge.

Reading systick is done on internal Cortex bus => very low latency, cycle precise. Btw. even if any jitter might be induced, the whole MCU would be delayed with the same amount of time => it's still cycle precise :)

[Tesla DeLorean]

Posted on May 17, 2011 at 13:43

Using Timer 4, less resolution/precision, 16-bit register

{

  TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);

  TIM_DeInit(TIM4);

  TIM_TimeBaseStructure.TIM_Period = 0xffff;

  TIM_TimeBaseStructure.TIM_Prescaler = 15;

  TIM_TimeBaseStructure.TIM_ClockDivision = 0x0;

  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure );

  //TIM_ARRPreloadConfig(TIM4, ENABLE);

  TIM4->EGR |= 0x01;

}

{

  u16 tim[2];

  int i;

  for(i=0; i<10; i++)

  {

    u32 a, b;

    a = SystemTick;

    do

    {

      b = SystemTick;

    } while(a == b);

    tim[0] = TIM4->CNT;

    TIM4->CR1 |= 1;

    Sleep(10);

    TIM4->CR1 &= ~1;

    tim[1] = TIM4->CNT;

    tim[1] = tim[1] - tim[0];

    printf(''%10d cycles, %7.4lf ms\n'',tim[1],((16.0 / (CPUCLOCK * 1000.0)) * (double)tim[1]));

  }

  putchar('\n');

}

     22510 cycles, 10.0044 ms

     22510 cycles, 10.0044 ms

     22511 cycles, 10.0049 ms

     22511 cycles, 10.0049 ms

     22510 cycles, 10.0044 ms

     22511 cycles, 10.0049 ms

     22510 cycles, 10.0044 ms

     22510 cycles, 10.0044 ms

     22511 cycles, 10.0049 ms

     22510 cycles, 10.0044 ms

[slimbahri]

Posted on May 17, 2011 at 13:43

Hi Edison,

Would you explain this with more details please?

Slim