SysTick.CTRL register documentation

Posted on May 17, 2011 at 13:49

From RM0008 STM32 Reference Manual (13902.pdf)

Pg 71

''The RCC feeds the Cortex System Timer (SysTick) external clock with the AHB clock divided by 8. The SysTick can work either with this clock or with the Cortex clock (AHB), configurable in the SysTick Control and Status Register.''

HCLK is AHBCLK

The register you want to program is defined by ARM, not ST

http://books.google.com/books?id=T9heqSaErCcC&pg=PA147&lpg=PA147&dq=SysTick+Control+and+Status+Register&source=bl&ots=eNvsEdEc5z&sig=fWIFO_tBWbkN_a6-btdbkwiw_-Q&hl=en&ei=4UngS_CKLJTENpTz7c4J&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCMQ6AEwAw#v=onepage&q=SysTick%20Control%20and%20Status%20Register&f=false

The clocks used by ARM are either SYSCLK, or the external clock (in this case ST's HCLK/8). I don't think the HCLK/1 is used, but it would be easy to check.

I use HCLK/8, because a 1ms tick doesn't need to be clocking at an excessively high rate

SysTick_CLKSourceConfig(SysTick_CLKSource_HCLK_Div8);

void SysTick_CLKSourceConfig(u32 SysTick_CLKSource)

{

  /* Check the parameters */

  assert_param(IS_SYSTICK_CLK_SOURCE(SysTick_CLKSource));

  if (SysTick_CLKSource == SysTick_CLKSource_HCLK)

  {

    SysTick->CTRL |= SysTick_CLKSource_HCLK;

  }

  else

  {

    SysTick->CTRL &= SysTick_CLKSource_HCLK_Div8;

  }

}