/**
*
* @brief Initialize the tickless idle feature
*
* This routine initializes the tickless idle feature by calculating the
* necessary hardware-specific parameters.
*
* Note that the maximum number of ticks that can elapse during a "tickless idle"
* is limited by <default_load_value>. The larger the value (the lower the
* tick frequency), the fewer elapsed ticks during a "tickless idle".
* Conversely, the smaller the value (the higher the tick frequency), the
* more elapsed ticks during a "tickless idle".
*
* @return N/A
*/
static void sysTickTicklessIdleInit(void)
{
/* enable counter, disable interrupt and set clock src to system clock
*/
u32_t ctrl = SysTick_CTRL_ENABLE_Msk | SysTick_CTRL_CLKSOURCE_Msk;
volatile u32_t dummy; /* used to help determine the 'skew time' */
/* store the default reload value (which has already been set) */
default_load_value = sysTickReloadGet();
/* calculate the max number of ticks with this 24-bit H/W counter */
max_system_ticks = 0x00ffffff / default_load_value;
/* determine the associated load value */
max_load_value = max_system_ticks * default_load_value;
/*
* Calculate the skew from switching the timer in and out of idle mode.
* The following sequence is emulated:
* 1. Stop the timer.
* 2. Read the current counter value.
* 3. Calculate the new/remaining counter reload value.
* 4. Load the new counter value.
* 5. Set the timer mode to periodic/one-shot.
* 6. Start the timer.
*
* The timer must be running for this to work, so enable the
* systick counter without generating interrupts, using the processor
*clock.
* Note that the reload value has already been set by the caller.
*/
SysTick->CTRL |= ctrl;
__ISB();
timer_idle_skew = sysTickCurrentGet(); /* start of skew time */
SysTick->CTRL |= ctrl; /* normally sysTickStop() */
dummy = sysTickCurrentGet(); /* emulate sysTickReloadSet() */
/* emulate calculation of the new counter reload value */
if ((dummy == 1) || (dummy == default_load_value)) {
dummy = max_system_ticks - 1;
dummy += max_load_value - default_load_value;
} else {
dummy = dummy - 1;
dummy += dummy * default_load_value;
}
/* _sysTickStart() without interrupts */
SysTick->CTRL |= ctrl;
timer_mode = TIMER_MODE_PERIODIC;
/* skew time calculation for down counter (assumes no rollover) */
timer_idle_skew -= sysTickCurrentGet();
/* restore the previous sysTick state */
sysTickStop();
sysTickReloadSet(default_load_value);
#ifdef CONFIG_TICKLESS_KERNEL
idle_original_ticks = 0;
#endif
}
/**
*
* @brief Initialize the tickless idle feature
*
* This routine initializes the tickless idle feature by calculating the
* necessary hardware-specific parameters.
*
* Note that the maximum number of ticks that can elapse during a "tickless idle"
* is limited by <default_load_value>. The larger the value (the lower the
* tick frequency), the fewer elapsed ticks during a "tickless idle".
* Conversely, the smaller the value (the higher the tick frequency), the
* more elapsed ticks during a "tickless idle".
*
* @return N/A
*/
static void sysTickTicklessIdleInit(void)
{
/* enable counter, disable interrupt and set clock src to system clock
*/
union __stcsr stcsr = {.bit = {1, 0, 1, 0, 0, 0} };
volatile uint32_t dummy; /* used to help determine the 'skew time' */
/* store the default reload value (which has already been set) */
default_load_value = sysTickReloadGet();
/* calculate the max number of ticks with this 24-bit H/W counter */
max_system_ticks = 0x00ffffff / default_load_value;
/* determine the associated load value */
max_load_value = max_system_ticks * default_load_value;
/*
* Calculate the skew from switching the timer in and out of idle mode.
* The following sequence is emulated:
* 1. Stop the timer.
* 2. Read the current counter value.
* 3. Calculate the new/remaining counter reload value.
* 4. Load the new counter value.
* 5. Set the timer mode to periodic/one-shot.
* 6. Start the timer.
*
* The timer must be running for this to work, so enable the
* systick counter without generating interrupts, using the processor
*clock.
* Note that the reload value has already been set by the caller.
*/
__scs.systick.stcsr.val |= stcsr.val;
__asm__(" isb"); /* ensure the timer is started before reading */
timer_idle_skew = sysTickCurrentGet(); /* start of skew time */
__scs.systick.stcsr.val |= stcsr.val; /* normally sysTickStop() */
dummy = sysTickCurrentGet(); /* emulate sysTickReloadSet() */
/* emulate calculation of the new counter reload value */
if ((dummy == 1) || (dummy == default_load_value)) {
dummy = max_system_ticks - 1;
dummy += max_load_value - default_load_value;
} else {
dummy = dummy - 1;
dummy += dummy * default_load_value;
}
/* _sysTickStart() without interrupts */
__scs.systick.stcsr.val |= stcsr.val;
timer_mode = TIMER_MODE_PERIODIC;
/* skew time calculation for down counter (assumes no rollover) */
timer_idle_skew -= sysTickCurrentGet();
/* restore the previous sysTick state */
sysTickStop();
sysTickReloadSet(default_load_value);
}
