sys/xtimer: Avoid race incrementing multiple periods in _timer_callback #4000
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On a fast CPU with a slow timer (e.g. XTIMER_SHIFT > 0) it is possible that now == _xtimer_now() when spinning for the overflow. In the extreme case When this happens _next_period() will be called more than once until the timer overflows for real. Fault observed in real life when running on a 32.768 kHz timer on a ~96 MHz clocked mulle (Kinetis K60, Cortex-M4). _next_period() was called 9 times during the same ISR call before the 32 kHz timer overflowed.
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HAPPY 4000 everyone!! 🍻 |
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Change was ACK'd by @kaspar030 in #3998 already, so ACK here too. |
miri64
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Sep 30, 2015
…-2015.09 sys/xtimer: Avoid race incrementing multiple periods in _timer_callback
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2015.09 release version of #3998
On a fast CPU with a slow timer (e.g. XTIMER_SHIFT > 0) it is possible
that now == _xtimer_now() when spinning for the overflow. In the extreme
case When this happens _next_period() will be called more than once
until the timer overflows for real.
Fault observed in real life when running on a 32.768 kHz timer on a
~96 MHz clocked mulle (Kinetis K60, Cortex-M4). _next_period() was
called 9 times during the same ISR call before the 32 kHz timer
overflowed.