Custom FPGA Data Acquisition for Experimental Astrophysics
Field-Programmable Gate Array (FPGA) technology is becoming more advanced and commercially accessible with many off-the-shelf options available for a variety of applications ranging from the casual hobbyist to leading edge hardware development research requiring precision real-time operation. FPGAs allow for task-configurable, customizable designs, which can be highly optimized for specific applications. FPGAs are also very easily reconfigurable for other appications via software modification, and are thus very useful for use in an experimental physics laboratory. The Digilent Cmod A7 available for ~$90 USD was selected as an ideal solution for an application requiring 43 digital I/O pins, sub-microsecond level timing accuracy, and a state-machine cycle rates in excess of 100 kHz. This work presents the use of the CmodA7 FPGA module as part of a custom electronic data acquisition system for a laboratory-based interferometry testbed supporting the development of instrument concepts and techniques for experimental astrophysics. Using serial communication over a custom Universal Asynchronous Receiver- Transmitter (UART) designed in the Verilog hardware descriptive language, we demonstrated non-standard serial baud rates up to 4 Mbps, allowing for serial transmission rates over 2 Mbps. This work presents the validation of this data acquisition (DAQ) system, and identification of the barriers to higher data rates through the UART interface. We also present preliminary results from other FPGA interface options using USB and ethernet communication which all significantly higher data rates, at the cost of increased complexity in FPGA design and the associated development and validation cycle(s).