Where are you running Linux that affects the C6748? I assume you are not running Linux on the C6748, so this leaves me confused.
Please find an example program and try to get the serial port working with that. If it does not work and you get the RFULL in that case, It will be easier to get some discussion going about code problems. If it does work, then you have an example to compare against the custom code you have written yourself.
Sivaraj may have some suggestions for drivers and examples. I do not.
Regards,
RandyP