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[Time] delayMicroseconds() accuracy + Fix ticks per ms value used to compute micros #620

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Merged
merged 2 commits into from
Sep 2, 2019
Merged

[Time] delayMicroseconds() accuracy + Fix ticks per ms value used to compute micros #620

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3f01812
[Time] Fix ticks per ms value used to compute micros
fpistm Aug 29, 2019
a53ddd0
[Time] delayMicroseconds() accuracy
fpistm Aug 29, 2019
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7 changes: 4 additions & 3 deletions cores/arduino/stm32/clock.c
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Original file line number Diff line number Diff line change
Expand Up @@ -53,12 +53,13 @@ uint32_t getCurrentMicros(void)
/* Ensure COUNTFLAG is reset by reading SysTick control and status register */
LL_SYSTICK_IsActiveCounterFlag();
uint32_t m = HAL_GetTick();
uint32_t u = SysTick->LOAD - SysTick->VAL;
const uint32_t tms = SysTick->LOAD + 1;
__IO uint32_t u = tms - SysTick->VAL;
if (LL_SYSTICK_IsActiveCounterFlag()) {
m = HAL_GetTick();
u = SysTick->LOAD - SysTick->VAL;
u = tms - SysTick->VAL;
}
return (m * 1000 + (u * 1000) / SysTick->LOAD);
return (m * 1000 + (u * 1000) / tms);
}

/**
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16 changes: 14 additions & 2 deletions cores/arduino/wiring_time.h
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Expand Up @@ -69,8 +69,20 @@ static inline void delayMicroseconds(uint32_t us)

while ((int32_t)dwt_getCycles() - start < cycles);
#else
uint32_t start = getCurrentMicros();
while (getCurrentMicros() - start < us);
__IO uint32_t currentTicks = SysTick->VAL;
/* Number of ticks per millisecond */
const uint32_t tickPerMs = SysTick->LOAD + 1;
/* Number of ticks to count */
const uint32_t nbTicks = ((us - ((us > 0) ? 1 : 0)) * tickPerMs) / 1000;
/* Number of elapsed ticks */
uint32_t elapsedTicks = 0;
__IO uint32_t oldTicks = currentTicks;
do {
currentTicks = SysTick->VAL;
elapsedTicks += (oldTicks < currentTicks) ? tickPerMs + oldTicks - currentTicks :
oldTicks - currentTicks;
oldTicks = currentTicks;
} while (nbTicks > elapsedTicks);
#endif
}

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