The following ports used 65536 as the upper value (100% duty cycle) and are
changed in this commit to use 65535: esp8266, mimxrt, nrf, samd.
Tested that output is high at `duty_u16(65535)` and low at `duty_u16(0)`.
Also verified that at `duty_u16(32768)` the high and low pulse have the
same length.
Partially reverts #10850, commits 9c7ad68165
and 2ac643c15b.
Signed-off-by: robert-hh <robert@hammelrath.com>
This adds the freq and duty_u16 keyword settings to the constructor, and
sometimes other details in the PWM section.
For mimxrt a clarification regarding the PWM invert argument was added, and
for rp2 a few words were spent on PWM output pairs of a channel/slice.
In that case, no Pin will be configured for the CS signal, even if it is
internally still generated. That setting allows to use any pin for CS,
which then must be controlled by the Python script.
Also make the default cs=-1 to match other ports (software CS).
