The ARM CortexM3 (and later) chips almost always have a 32bit timer in
the "Debug and Watch Trace" (DWT) unit which resides within the cpu
core itself. This timer is generally faster to access than timers
located on the chip's peripheral bus. When combined with the standard
ARM SysTick timer it provides a (generally) portable mechanism to
implement Klipper's software timer mechanism. It's generally also
faster than using the vendor specific timers.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
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