  Due to the advantages of universality, flexibility and high performance, fast
Ethernet is widely used in readout system design of modern particle physics
experiments. However, Ethernet is usually used together with TCP/IP protocol
stack, which makes it difficult to be implemented because designers have to use
operating system to process this protocol. Furthermore, TCP/IP protocol
degrades the transmission efficiency and real-time performance. To maximize the
performance of Ethernet in physics experiment applications, a data readout
method based on physical layer (PHY) is proposed in this paper. In this method,
TCP/IP protocol is forsaken and replaced with a customized and simple protocol,
which make it easier to be implemented. On each readout module, data from
front-end electronics is first fed into an FPGA for protocol processing and
then sent out to a PHY chip controlled by this FPGA for transmission. This kind
of data path is fully implemented by hardware. While from the side of data
acquisition system (DAQ), absence of standard protocol makes the network
related applications panic. To solve this problem, in the operating system
kernel space, data received by network interface card is drawn away from the
traditional flow and redirected to a specified memory space by a customized
program. This memory space can be easily accessed by applications in user
space. For the purpose of verification, a prototype system is designed and
implemented. Preliminary test result shows that this method can meet the
requirement of data transmission from readout module to DAQ with good
efficiency and simplicity.
