Add a new DT property named "pixel-group-size" that allows users to
configure the driver to refresh the matrix by illuminating multiple
LEDs in particular rows simultaneously. This way the maximum possible
brightness of the LEDs can be increased (as they can be lit longer)
and the timer interrupt handler is executed less frequently, what
results in decreased CPU load, but more GPIOTE/PPI channels needs to
be allocated if the PWM peripheral cannot be used. Thus, it is left
to users to select the configuration that suits them best.
Update definitions of both the bbc_microbit boards with this new
property, using the maximum available group size (to achieve maximum
possible brightness). For v2, no new resources are used (only all
channels in the already used PWM peripheral are now utilized).
For v1, two more GPIOTE and PPI channels are allocated.
Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>
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