/* Set the SysTick Clock Source. 
The clock source can be either the AHB clock or the same clock divided by 8. */
void systick_set_clocksource(uint8_t clocksource)
/* Set the SysTick Clock Source. 
The clock source can be either the AHB clock or the same clock divided by 8. */
void systick_set_clocksource(uint8_t clocksource)
{
	STK_CSR = (STK_CSR & ~STK_CSR_CLKSOURCE) |
		  (clocksource & STK_CSR_CLKSOURCE);
}