A general purpose Ethernet based readout data acquisition system

A flexible dedicated readout system is one of the most important part of any kind of dedicated detection system, especially for its testing phase as well as when the final system is ready for implementation. An obvious choice is to use a FPGA (apart from dedicated front-end electronics) as a first stage of data storage and processing element. Furthermore the FPGA has to prepare and transfer the incoming/processed data to the host PC. The implementation of the data exchange can be a problem, especially for small groups of developers, who have an option to buy a general solution with its limitations and a price, or to do time-consuming development of their own system practically from scratch. This paper presents a FPGA based general purpose readout solution which lies in between the two opposite approaches. Presented system uses a FPGA mezzanine board equipped with Ethernet Gigabit connection to PC. The FPGA FIFO based readout of a digital data stream is packed directly into the Ethernet frames and send to the destination PC using point-to point connection. The standard Ethernet frames are used in this design, additionally equipped with one byte carrying information on data type. When a high throughput is needed the data type is employed to prioritize them. This moderately simple but very powerful interface is relatively easy to be implemented in many applications [1]. The custom approach chosen for FPGA implementation causes a need to prepare dedicated software suite to process all incoming data in the PC side. The developed software package is called EPPRO (Ethernet Packet PROxy) since it exploits special Ether net frames for data exchange. The core part of EPPRO is a Linux kernel module, responsible for data reception/transmission and dispatching, taking into account their types to filter and prioritize the incoming packets. Overall performance of the whole system has been evaluated in respect to its throughput and reliability, presented test results confirm that all of the design goals have been fulfilled.