Failed to read UART with non blocking mode

Hi

I am working with Altera FPGA DE2 with with Nios II 13.0sp1 Software Build Tools for Eclipse, first I worked with UART with blocking mode using open(), read() and write() functions, It worked fine, but when I change to non blocking mode (I added O_NONOBLOCK to the open function), but the read call fails, it returns -1, and then I read the errno value and it was 12 which corresponds to ENOMEM. I have found a similar post but it was not answered. Is that a way to fix this ?

Any idea or comment is welcomed
Thank you in advance