Posted on July 10, 2014 at 21:55
SysTick is an Interrupt (System Handler), you define the periodicity that this is called.
You configure it with ticks of the system clock, it figures out which source (SYSCLK, vs HCLK/8) depending on the number of ticks, and the fact the counter has only 24-bit.
Only supports a single periodicity, ie 1 ms, if you want 1s and 1ms you'd count off 1000 milliseconds, then do the 1Hz task.
It is NOT a delay function.
Review an example:
STM32F4xx_DSP_StdPeriph_Lib_V1.3.0\Project\STM32F4xx_StdPeriph_Examples\SysTick\SysTick_Example\main.c
/* Setup SysTick Timer for 1 msec interrupts.
------------------------------------------
1. The SysTick_Config() function is a CMSIS function which configure:
- The SysTick Reload register with value passed as function parameter.
- Configure the SysTick IRQ priority to the lowest value (0x0F).
- Reset the SysTick Counter register.
- Configure the SysTick Counter clock source to be Core Clock Source (HCLK).
- Enable the SysTick Interrupt.
- Start the SysTick Counter.
2. You can change the SysTick Clock source to be HCLK_Div8 by calling the
SysTick_CLKSourceConfig(SysTick_CLKSource_HCLK_Div8) just after the
SysTick_Config() function call. The SysTick_CLKSourceConfig() is defined
inside the misc.c file.
3. You can change the SysTick IRQ priority by calling the
NVIC_SetPriority(SysTick_IRQn,...) just after the SysTick_Config() function
call. The NVIC_SetPriority() is defined inside the core_cm3.h file.
4. To adjust the SysTick time base, use the following formula:
Reload Value = SysTick Counter Clock (Hz) x Desired Time base (s)
- Reload Value is the parameter to be passed for SysTick_Config() function
- Reload Value should not exceed 0xFFFFFF
*/
if (SysTick_Config(SystemCoreClock / 1000))
{
/* Capture error */
while (1);
}
/**
* @brief This function handles SysTick Handler.
* @param None
* @retval None
*/
void SysTick_Handler(void)
{
TimingDelay_Decrement();
}
