Thanks for your reply Todd. In fact, I am using QNX on beaglebone which has an ARM am335x processor. I am trying to write C code to transmit messages on a self test loop-back mode. I find a library provided in the BSP of QNX for beagle bone but I guess this library doesn’t work. I am having an issue with sending a cmd message to the IF/IF2 message control command register . QNX crashes and reboot.