When initializing serial disable all interrupts as some of these may
have been enabled by a bootloader. This ensures that the NRF52
serial driver remains compatible with any bootloader version.
Make the following enhancement:
-Support serial port use without flow control
-Prevent dropped bytes by updating flow control handling
-Remove dead code
Serial port use without flow control:
In the prior implementation there was a window of time between
reloading DMA buffers after a timeout where bytes could be dropped.
This is because the uart needed to be turned off in order to flush the
bytes in the DMA buffer.
This change configures the DMA buffer to only receive one byte at a
time so there is no need to disable the uart to flush it. After each
byte is received the DMA transfer will be over so the transfer will
never be partially complete and need flushing. Since the uart is
always on it is safe to use it even without flow control.
Prevent dropped bytes by updating flow control handling:
To prevent dropped bytes due to high latency the flow control handling
of the RTS line was configured to be asserted automatically by
hardware after each byte. Once the CPU has read the byte and setup
the next receive buffer the RTS line is deasserted to the transfer can
continue. This ensure that when flow control is enabled data won't be
lost due to interrupt latency.
Remove dead code:
With the above changes there is a lot of dead code, such as the timer
handling code. This patch removes the code that is no longer used.
Busy-wait before sending a charecter instead of after. If
serial_writeable has been called first, the busy-wait loop will
be skipped.
Added initialization code to ensure NRF_UARTE_EVENT_TXDRDY is
armed correctly.
In nordic_nrf5_uart_event_handler if the events NRF_UARTE_EVENT_ENDRX
and NRF_UARTE_EVENT_RXSTARTED become pending after the check for
NRF_UARTE_EVENT_ENDRX but before the check for
NRF_UARTE_EVENT_RXSTARTED the RX DMA buffers will be setup incorrectly
by nordic_nrf5_uart_event_handler_rxstarted because active_bank hasn't
been updated. This cause dropped and incorrect data.
This patch fixes that problem by adding a second check for
NRF_UARTE_EVENT_ENDRX after checking for NRF_UARTE_EVENT_RXSTARTED
and skipping processing if NRF_UARTE_EVENT_ENDRX is set. The
subsequent interrupt will process both in the correct order. This
ensures that these events cannot be handled out of order and thus fixes
the corruption.
Martin Kojtal
Russ Butler
Cruz Monrreal II
Russ Butler
Senthil Ramakrishnan
Marcus Chang
Brian Daniels
Aashish chaddha
jeromecoutant
Mahesh Mahadevan
Teppo Järvelin
Qinghao Shi