UART - Raspberry Pi Hardware Reference - page 104

tcflush(3)
The tcflush(3) call can be used to flush pending input or output data from the serial
port buffers.

int tcflush(int fd, int queue_selector);

where
fd is the open TTY file descriptor.
queue_selector determines which queue(s) are to be flushed.
The following values are used for the queue_selector argument :

queue_selector Description

TCIFLUSH Flushes unread incoming data

TCOFLUSH Flushes untransmitted output data

TCIOFLUSH Flushes both unread and untransmitted data

The following example flushes pending input data:

int rc;

rc = tcflush(fd,TCIFLUSH);

tcflow(3)
Various flow control operations can be performed by calling the tcflow(3) function:

int tcflow(int fd, int action);

where
fd is the open TTY file descriptor.
action is the flow control action required (as shown in the following table).
The valid choices for action are as follows:

action Description

TCOOFF Suspends output (transmission stops)

TCOON Resumes output

TCIOFF Immediately sends a STOP character to stop the remote device

TCION Transmits a START character to resume the remote device