I have an Astar32u4 micro that I setup according to your user guide and connected to a USB port on an iMac running OS X 10.10.5 (Yosemite). I developed a test program based on the LUFA GenericHID device and host app that functions properly to enumerate and exchange reports between the device and host.
During development the device was programmed many times using avrdude at device /dev/tty.usbmodem1451. The board was simply stuck on a breadboard with no wiring connection except the USB cable. Everything worked fine.
I proceeded to integrate the Astar32u4 into a simple x-y display controller. The Astar32u4 is powered by the USB bus, and has output connections at PB4-7, RST, 3V3, GND and PB1,2(SDI,SCK) for SPI IO. All other pins are unconnected. The 3V3 pin is used as a voltage reference.
After the integration, the Astar32u4 enumerates correctly and runs the device firmware correctly but no /dev/tty device is created in the host upon connecting the USB port .
I disconnected the wiring connections and moved the device from the controller back to the breadboard and now it still will not cause the /dev/tty device to be created upon connection. This behave the same on the iMac and a Macbook-pro running OS X 10.10.1.
What could I have mistreated to cause this strange USB behavior?