Hello Jeff,
On 02.03.23 22:57, jeff.hat...@l3harris.com wrote:
I am working on a project that uses the RTEMS OS on a Leon3 processor. I
am trying to read/write from a UART that is connected up through the
termios interface. It works for the most part but I am running into an
issue with flushing and reading from the UART. It seems if I read a
small portion of the data use read() then flush then read again there is
still data returned. Is this expected behavior? If so is there any way
to clear out whatever is cached in read?
Pseudo Code
Open UART with open("/dev/console_b", O_RDWR | O_NONBLOCK); setup
terminal into raw mode with cfmakeraw() and tcsetattr(fd,
TCSADRAIN,term)
Setup the UART into loop back mode so its TX data is looped back into
its RX Write data into UART with write(fd, "TEST",4) Read a single
character with read(fd, buff, 1); buff will contain "T" here flush
buffers with tcflush(fd, TCIOFLUSH) Read a more from UART with read(fd,
buff, 3); Would expect nothing is returned here but "EST" will be returned.
this could be a limitation of the current Termios implementation. It
doesn't flush device buffers:
static void
flushInput (struct rtems_termios_tty *tty)
{
rtems_termios_device_context *ctx = tty->device_context;
rtems_interrupt_lock_context lock_context;
rtems_termios_device_lock_acquire (ctx, &lock_context);
tty->rawInBuf.Tail = 0;
tty->rawInBuf.Head = 0;
rtems_termios_device_lock_release (ctx, &lock_context);
}
If the characters are still in the UART FIFO, then they are not flushed.
This could be fixed by calling the device ioctl handler in this function
and additional device-specific handling.
--
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