Timers

[dmwarnke]

Posted on October 09, 2012 at 18:13

I am new to the 32-bit world and am trying to generate an interruptable timer every 5us or so.

The application is an A/D read and the the channel has to settle for 30us before a read can occur. I am currently using the STM32L Discovery board because we will be using a similar chip for our platform.

I tried using the systick but the best resolution I can get out of that is 20us at 32MHz.

Any suggestions or something I have overlooked. Im coming from an 8-bit world mostly using Atmels and Freescales so Im unfamiliar with ST peripheral usage.

Regards,

Doug 

#timers

[Tesla DeLorean]

Posted on October 09, 2012 at 19:54

I tried using the systick but the best resolution I can get out of that is 20us at 32MHz.

Should be able to get resolution/granularity of 250ns from SysTick

A regular timer, depending on the period, should be able to get 31.25ns granularity in setting. Program the timebase, prescale = 0, period = 640 - 1, and enable the update interrupt.

A bigger issue might be that you only have 640 cycles to play with.

[Tesla DeLorean]

Posted on October 09, 2012 at 20:01

STM32L1xx_StdPeriph_Lib_V1.1.1\Project\STM32L1xx_StdPeriph_Examples\SysTick\SysTick_Example\main.c

  if (SysTick_Config(SystemCoreClock / 50000))

  {

    /* Capture error */

    while (1);

  }

STM32L1xx_StdPeriph_Lib_V1.1.1\Project\STM32L1xx_StdPeriph_Examples\TIM\TimeBase\main.c

  /* Time base configuration */

  TIM_TimeBaseStructure.TIM_Period = 640 - 1; // Where TIMCLK2 = 32 MHz, 50 KHz timebase

  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);