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drivers: timer: systick: fix off-by-one setting in tickless mode

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When the counter reaches zero, it reloads the value in
SYST_RVR on the next clock edge. This means that if the
LOAD value is N, the interrupt ("tick") is triggered
every N+1 cycles. Therefore, when we operate in tickless
mode, and we want to schedule the next timeout, we need
to configure the LOAD value with last_load - 1, in order
to get an event in last_load cycles.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
This commit is contained in:
Ioannis Glaropoulos 2019-04-11 12:53:17 +02:00 • committed by Anas Nashif
commit a0a861bfd7
1 changed files with 1 additions and 1 deletions
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2
drivers/timer/cortex_m_systick.c
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@ -144,7 +144,7 @@ void z_clock_set_timeout(s32_t ticks, bool idle)
last_load = delay - (cycle_count - announced_cycles);
overflow_cyc = 0U;
SysTick->LOAD = last_load;
SysTick->LOAD = last_load - 1;
SysTick->VAL = 0; /* resets timer to last_load */
k_spin_unlock(&lock, key);