Prior to this fix, if the UART hardware FIFO had a few chars but still
below the FIFO trigger threshold, and the ringbuf was empty, the read
function would timeout if timeout==0 (the default timeout).
This fix follows the suggestion of @iabdalkader.
The RX IRQ does not trigger if the FIFO is less than the trigger level, in
which case characters may be available in the FIFO, yet not in the ringbuf,
and the ioctl returns false.
Instantiation and init now support the rxbuf and txbuf keywords for setting
the buffer size. The default size is 256 bytes. The minimum and maximum
sizes are 32 and 32766 respectively.
uart.write() still includes checks for timeout, even if it is very unlikely
to happen due to a) lack of flow control support and b) the minimal timeout
values being longer than the time it needs to send a byte.
This commit adds a new port "rp2" which targets the new Raspberry Pi RP2040
microcontroller.
The build system uses pure cmake (with a small Makefile wrapper for
convenience). The USB driver is TinyUSB, and there is a machine module
with most of the standard classes implemented. Some examples are provided
in the examples/rp2/ directory.
Work done in collaboration with Graham Sanderson.
Signed-off-by: Damien George <damien@micropython.org>
