kinetis: periph/timer use LPTMR for TIMER_0, PIT for TIMER_1, TIMER_2 #4065
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This was referenced Oct 23, 2015
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Rebased on top of latest #3990 |
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added 12 commits
February 28, 2016 12:28
- Safer handling of targets when using XTIMER_MASK - Reduce number of redundant branches - Avoid possible timer underflow when subtracting XTIMER_OVERHEAD - Spin at the end if target time is close
…CKOFF If XTIMER_OVERHEAD is greater than either XTIMER_BACKOFF and/or XTIMER_ISR_BACKOFF then it will be possible schedule low level timers with a negative offset, which means the timer will delay until the next overflow.
64-bit version of div_u32_by_15625div512 also updated tests-div to use correct order for expected and actual values in unit tests (embUnit)
Set XTIMER_HZ in periph_conf.h to specify the xtimer hardware timer frequency. The xtimer system uses the hardware timer's own tick representation internally but a thin wrapper layer is added as a shim between xtimer core and the public xtimer API which is based around microseconds as the time unit. Initially supports only 1000000 Hz (and powers-of-two divisions of it) and 32768 Hz, but can easily be expanded by adding a new case for XTIMER_HZ inside xtimer.h
added 15 commits
February 28, 2016 12:28
- drift is the total difference from the expected time - jitter is the difference only since the last printout
… timers, and the 2**32 usec barrier
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Seems unlikely to get ready for this release. |
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closed in favour of #5294 |
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Depends on #3990,
#4040, #4827, #4183This PR modifies the periph/timer interface to use the low-power timer (LPTMR) for TIMER_0 and use that timer for the xtimer system. The LPTMR module has the benefit that it does not stop when entering any low power modes, so it can be used as a reliable timer source for a power saving radio MAC layer.
TIMER_1 and TIMER_2 are using the PIT module, which only runs when the CPU is in RUN or WAIT mode, i.e. full power.
The LPTMR module resets when stopping, so in order to prevent the timer from going backwards when setting a new time we use the RTT module as a reference point for
lptmr_read(). This avoids the convoluted (sometimes even ineffective) extra measures that were used in the old hwtimer implementation to avoid dropping ticks on the LPTMR module.This PR is somewhat controversial because it modifies the periph/timer driver to use three different hardware timers running at different frequencies.