Basic CMSIS Example

A typical example for using the CMSIS layer is provided below. The example is based on an unspecific Cortex-A9 Device.

#include <ARMCA9.h>                              // File name depends on device used
 
static const uint32_t TICK_RATE_HZ = 1000U;
 
uint32_t volatile msTicks;                       // Counter for millisecond Interval
 
static void SysTick_Handler( void )
{
  msTicks++;                                     // Increment Counter
}
 
// We use the Private Tiemer (PTIM) of the Cortex-A9 FVP Model here.
// In general the available Timers are highly vendor specific for Cortex-A processors.
void private_timer_init(void) {
 
  PTIM_SetLoadValue ((SystemCoreClock/TICK_RATE_HZ) - 1U);
  PTIM_SetControl (PTIM_GetControl() | 7U);

  /* Install SysTick_Handler as the interrupt function for PTIM */
  IRQ_SetHandler((IRQn_ID_t)PrivTimer_IRQn, SysTick_Handler);
 
  /* Determine number of implemented priority bits */
  IRQ_SetPriority ((IRQn_ID_t)PrivTimer_IRQn, IRQ_PRIORITY_Msk);
 
  /* Set lowest priority -1 */
  IRQ_SetPriority ((IRQn_ID_t)PrivTimer_IRQn, GIC_GetPriority((IRQn_ID_t)PrivTimer_IRQn)-1);
 
  /* Enable IRQ */
  IRQ_Enable ((IRQn_ID_t)PrivTimer_IRQn);
}

/* Delay execution for given amount of ticks */
void Delay(uint32_t ticks)  {
  uint32_t tgtTicks = msTicks + ticks;             // target tick count to delay execution to
  while (msTicks == tgtTicks)  {
    __WFE ();                                      // Power-Down until next Event/Interrupt
  }
}
 
/* main function */
int main(void)
{
  /* Initialize device HAL here */
  private_timer_init();
 
  static uint8_t ledState = 0;
 
  /* Infinite loop */
  while (1)
  {
    /* Add application code here */
    ledState = !ledState;
    Delay(500);
  }
}