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drivers: systick: Fix Cortex-M SysTick dropping 1 cycle per tick

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`last_load` is the full N cycles and `SysTick->LOAD` should
be loaded with `last_load - 1` for the calculations work
correctly.

Note: This only affects a kernel in ticked operation.
Tickless kernels periodically restart the timer correctly.

Signed-off-by: Grant Ramsay <gramsay@enphaseenergy.com>
This commit is contained in:
Grant Ramsay 2023-10-04 10:08:42 +13:00 committed by Fabio Baltieri
parent 1951d83783
commit 236318332b
1 changed files with 2 additions and 2 deletions
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4
drivers/timer/cortex_m_systick.c
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@ -314,9 +314,9 @@ static int sys_clock_driver_init(void)
{
NVIC_SetPriority(SysTick_IRQn, _IRQ_PRIO_OFFSET);
last_load = CYC_PER_TICK - 1;
last_load = CYC_PER_TICK;
overflow_cyc = 0U;
SysTick->LOAD = last_load;
SysTick->LOAD = last_load - 1;
SysTick->VAL = 0; /* resets timer to last_load */
SysTick->CTRL |= (SysTick_CTRL_ENABLE_Msk |
SysTick_CTRL_TICKINT_Msk |