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@ -432,25 +432,6 @@ void _xtimer_sleep(uint32_t offset, uint32_t long_offset);
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static inline void xtimer_spin_until(uint32_t value);
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/** @} */
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#if XTIMER_MASK
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#ifndef XTIMER_SHIFT_ON_COMPARE
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/**
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* @brief ignore some bits when comparing timer values
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*
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* (only relevant when XTIMER_MASK != 0, e.g., timers < 32bit.)
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*
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* When combining _lltimer_now() and _high_cnt, we have to get the same value in
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* order to work around a race between overflowing _lltimer_now() and OR'ing the
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* resulting values.
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* But some platforms are too slow to get the same timer
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* value twice, so we use this define to ignore some of the bits.
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*
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* Use tests/xtimer_shift_on_compare to find the correct value for your MCU.
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*/
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#define XTIMER_SHIFT_ON_COMPARE (0)
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#endif
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#endif
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#ifndef XTIMER_MIN_SPIN
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/**
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* @brief Minimal value xtimer_spin() can spin
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@ -461,12 +442,18 @@ static inline void xtimer_spin_until(uint32_t value);
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static inline uint32_t xtimer_now(void)
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{
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#if XTIMER_MASK
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uint32_t a, b;
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uint32_t latched_high_cnt, now;
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/* _high_cnt can change at any time, so check the value before
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* and after reading the low-level timer. If it hasn't changed,
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* then it can be safely applied to the timer count. */
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do {
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a = _lltimer_now() | _high_cnt;
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b = _lltimer_now() | _high_cnt;
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} while ((a >> XTIMER_SHIFT_ON_COMPARE) != (b >> XTIMER_SHIFT_ON_COMPARE));
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return b;
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latched_high_cnt = _high_cnt;
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now = _lltimer_now();
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} while (_high_cnt != latched_high_cnt);
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return latched_high_cnt | now;
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#else
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return _lltimer_now();
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#endif
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Ian Martin
7 years ago