How to determine num of chars to read from serial dev ?

How to (fast) determine number of chars
that are in serial device /dev/ser1 input buffer ?

Is there any info about num of chars to read
when armed notification fires ?
/returning num of chars to read in pulse value;

tcischars() or dev_ischars() or ioctl() with FIONREAD
are slow (they do devctl() that is: MsgSend());

There is no other way.

Why would you care about that, just read as much data as possible and every notification. If you want to make sure the read call doesn’t block, open it in NON_BLOCKING mode. The read will return with what ever data is available. Or you can use readcond but that’s a QNX6 specific call.