GPT timer driver previously used "restart mode", where the timer would
count to a given value, then rollover. In this mode, "Any write access
to the Compare register of Channel 1 will reset the GPT counter". Since
a write to the compare register takes affect after 1 cycle of the
module's bus clock, and the bus clock is not synchonized with the GPT
module's low frequency counter clock, writing to the compare register
will induce a counter reset, and can cause the GPT to lose time
synchronization. This can induce time drift over time.
To fix this, rework the GPT driver to use "free run" mode. Note that
free run mode is not used directly, rather the GPT is configured to
reset on a tick boundary at boot, and then the second compare register
is used to set capture points. This way, the GPT interrupt will always
fire at a tick boundary, and no calculations are needed to handle
the counter rollover.
Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>
f3a35c58d8