The Beagle Bone Blue comes with a preinstalled Debian 8 with Kernel 4.4.54-ti-r93 or similar. Do not upgrade to Debian 9 cause robitics cape will not work anymore. Also do not use any newer Kernel, this will cause the same problem. The latest Debian Images for your Beagle Bone Blue can be downloaded here.
You can also run the Beagle Bone Blue with a real-time Kernel. Check if there is already a RT-Kernel:
If not, download:
$ sudo apt-get install linux-image-4.4.49-ti-rt-r89
Do not use a newer one. Robotics Cape won't work anymore (ERROR: missing PINMUX driver). Reboot and delete the old kernel:
sudo apt remove --purge linux-image-4.4.54-ti-r93