gistfile1.c

#define NVIC_ST_CTRL_R(*((volatile uint32_t *)0xE000E010)) 
#define NVIC_ST_RELOAD_R(*((volatile uint32_t *)0xE000E014)) 
#define NVIC_ST_CURRENT_R(*((volatile uint32_t *)0xE000E018))
 
void SysTick_Init(void){
 NVIC_ST_CTRL_R = 0; // 1) disable SysTick during setup 
 NVIC_ST_RELOAD_R = 0x00FFFFFF; // 2) maximum reload value 
 NVIC_ST_CURRENT_R = 0; // 3) any write to CURRENT clears it 
 NVIC_ST_CTRL_R = 0x00000005; // 4) enable SysTick with core clock
} 

// The delay parameter is in units of the 80 MHz core clock(12.5 ns) 
void SysTick_Wait(uint32_t delay){
  NVIC_ST_RELOAD_R = delay-1;  // number of counts
  NVIC_ST_CURRENT_R = 0;       // any value written to CURRENT clears
  while((NVIC_ST_CTRL_R&0x00010000)==0){ // wait for flag
  }
}
// Call this routine to wait for delay*10ms
void SysTick_Wait10ms(uint32_t delay){
 unsigned long i; 
 for(i=0; i<delay; i++){
   SysTick_Wait(800000); // wait 10ms
}