Using TCDRAIN and CTI_TCDRAIN under QNX 4
Title: Using TCDRAIN and CTI_TCDRAIN under QNX 4
Keywords: TCDRAIN CTI_TCDRAIN QNX4
kdb: kdb-060
Distribution: external

tcdrain() function as supplied by Watcom/QSSL does not work
with Intellicon or NT960 drivers.

The reason for this is that the Watcom/QSSL function expects
the UART device to have a transmit FIFO of one byte.
Therefore, when the buffer between Dev and
Dev.ser/Dev.cti/Dev.nt960 is empty, tcdrain() assumes this
means that all bytes have been transmitted.

With Intellicon and NT960, there can be several kilobytes of
data on the card waiting to be transmitted yet tcdrain()
would indicate they have been transmitted.

To avoid this, CTI has introduced cti_tcdrain() that
operates like tcdrain() with the exception that
cti_tcdrain() does not return until there is no buffered
data on the Intellicon or NT960 left to transmit.

The proper use of cti_tcdrain() is in conjunction with
tcdrain(), thereby ensuring that the operating system's
buffers are empty and the card's buffers are empty.

An example follows:
	int	fd;
	fd = open( "/dev/nt1", O_RDWR );
	write( fd, "ATH" );
	tcdrain( fd );
	cti_tcdrain( fd );

When tcdrain returns, Dev's buffers have been emptied to the
card. When cti_tcdrain() returns, all data buffered on the
card has been transmitted.