45  * This local variable holds the amount of SysTick HW cycles elapsed
49  *  At an arbitrary point in time the "current" value of the SysTick
57  * This local variable holds the amount of elapsed SysTick HW cycles
70  * SysTick timer wraps ('overflows') and is used in the calculation
84  * case because the Cortex-m SysTick is not clocked in the low power
102  * re-program the SysTick.LOAD register, in sys_clock_set_timeout().
109  * - reprogramming of SysTick.LOAD must be clearing the SysTick.COUNTER
119 	uint32_t val1 = SysTick->VAL;	/* A */  in elapsed()
120 	uint32_t ctrl = SysTick->CTRL;	/* B */  in elapsed()
121 	uint32_t val2 = SysTick->VAL;	/* C */  in elapsed()
123 	/* SysTick behavior: The counter wraps after zero automatically.  in elapsed()
159 		(void)SysTick->CTRL;  in elapsed()
186 	 * LOAD value, just before entering the idle mode (SysTick is clocked) or right  in sys_clock_isr()
199 		/* In TICKLESS mode, the SysTick.LOAD is re-programmed  in sys_clock_isr()
233 		SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;  in sys_clock_set_timeout()
280 	val1 = SysTick->VAL;  in sys_clock_set_timeout()
311 	val2 = SysTick->VAL;  in sys_clock_set_timeout()
313 	SysTick->LOAD = last_load - 1;  in sys_clock_set_timeout()
314 	SysTick->VAL = 0; /* resets timer to last_load */  in sys_clock_set_timeout()
397 		 * the SysTick missed in idle state.  in sys_clock_idle_exit()
401 			 * very short or 0. SysTick usually has higher measurement  in sys_clock_idle_exit()
434 			SysTick->LOAD = last_load - 1;  in sys_clock_idle_exit()
435 			SysTick->VAL = 0; /* resets timer to last_load */  in sys_clock_idle_exit()
436 			SysTick->CTRL |= SysTick_CTRL_ENABLE_Msk;  in sys_clock_idle_exit()
443 	SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;  in sys_clock_disable()
452 	SysTick->LOAD = last_load - 1;  in sys_clock_driver_init()
453 	SysTick->VAL = 0; /* resets timer to last_load */  in sys_clock_driver_init()
454 	SysTick->CTRL |= (SysTick_CTRL_ENABLE_Msk |  in sys_clock_driver_init()