Dynamically Programmable DRU for High-Speed Serial I/O
Paolo Novellini, Giovanni Guasti · 2010
Multi-service optical networks today require the availability of transceivers that can operate over a wide range of input data rates. High-speed serial I/O has a native lower limit for operating data rates, preventing easy interfacing to low-speed client signals. The non-integer data recovery unit (NI-DRU) presented in this application note is specifically designed for RocketIO ™ GTP and GTX transceivers in Virtex®-5 LXT, SXT, TXT, and FXT platforms and consists of look-up tables (LUTs) and flip-flops. The NI-DRU extends the lower data rate limit to 0 Mb/s and the upper limit to 1,250 Mb/s, making embedded high-speed transceivers the ideal solution for true multi-rate serial interfaces. The NI-DRU’s operational settings (data rate, jitter bandwidth, input ppm range, and jitter peaking) are dynamically programmable, thus avoiding the need for bitstream reload or partial reconfiguration. Operating on a synchronous external reference clock, the NI-DRU supports fractional oversampling ratios. Thus, only one BUFG is needed, independent of the number of channels being set up, even if all channels are operating at different data rates. Given the absence of a relationship between the reference clock and incoming data rate, two optional barrel shifters ease the interfacing of the NI-DRU with an external FIFO and/or with any required decoder. The first barrel shifter has a 10-bit output that can be easily coupled to an 8B/10B or 4B/5B decoder (both not included in the reference design). The second barrel shifter has a 16-bit output and is specifically designed for 8-bit protocols, such as SONET/SDH. Other barrel shifters can be designed by the user.