See https://github.com/micropython/micropython/issues/1736 for the
list of complications. This workaround instead of duplicating REPL
to another stream, switches to it, because read(STDIN) we use otherwise
is blocking call, so it and custom REPL stream can't be used together.
PWM implementation uses a timer and interrupts (FRC1), taken from
Espressif's/NodeMCU's implementation and adapted for our use.
8 channels are supported, on pins 0, 2, 4, 5, 12, 13, 14, 15.
Usage:
import machine
pwm0 = machine.PWM(machine.Pin(0))
pwm0.freq(1000)
pwm0.duty(500)
Frequency is shared (ie the same) for all channels. Frequency is
between 1 and 1000. Duty is between 0 and 1023.
Per POSIX http://pubs.opengroup.org/onlinepubs/9699919799/functions/send.html :
"If space is not available at the sending socket to hold the message to be
transmitted, and the socket file descriptor does not have O_NONBLOCK set,
send() shall block until space is available. If space is not available at the
sending socket to hold the message to be transmitted, and the socket file
descriptor does have O_NONBLOCK set, send() shall fail [with EAGAIN]."
Paul Sokolovsky
Damien George