High-Speed, Fixed-Latency Serial Links With FPGAs for Synchronous Transfers

Fixed-latency serial links find application in trigger and data acquisition systems of High Energy Physics (HEP) experiments requiring a predictable data transfer timing. In some architectures, there is the need to clock the data in and out front the link synchronously with a system clock (i.e., synchronous transfers) instead of using the clock recovered from the serial stream. In this work, we present a synchronous link architecture based on high-speed transceivers embedded in latest generation Field Programmable Gate Arrays (FPGAs). These transceivers are typically designed for applications that tolerate latency variations. However, we have developed two configurations and a clocking scheme to implement fixed-latency operation. The latency is constant during the transfer, after a loss of lock or a power cycle. Once locked, the link can be considered as a synchronous pipeline. The configurations do not depend on a particular serial encoding, the encoder/decoder being external to the transceiver. We discuss the latency performance for each configuration and show an implementation of the architecture we propose. We also present experimental results showing the stability of the latency of the link.