Hey guys, Be careful when using Virtex5 for SONET. The RocketIO tile only has 1 PLL used for transmit and receive on both bidirectional ports. This PLL is normally sync'd to the local reference so the transmit data is on the local clock rather than the network clock (recovered clock). This architecture leads to all sorts of problems. Xilinx is recommending that a crystal controlled VCO oscillator be used for the local reference per XAPP649 (old Virtex2 app note) but this entails designing a phase comparator and analog filter. Even if you do this, your stuck with the second transmitter sync'd to the recovered clock of the first port. In our application we would like to use the second port for Ethernet in a POS application (can't be done). In order to make this work, the application software has to keep track of where the recovered clock is coming from and the clocks from several ports need to be muxed to select which recovered clock is used for the VCO reference. See what I mean?
- posted
16 years ago