AR# 37659

描述

This Answer Record discusses how to implement the updated line rates for the Spartan-6 FPGA GTP Transceiver in the Spartan-6 FPGA GTP Transceiver Wizard.

The Spartan-6 FPGA Data Sheet (v1.9) (DS162) has updated the supported line rate ranges from 0.6 to 0.81; 1.2 to 1.62; and 2.4 to 3.125Gb/s seen in previous data sheets to 0.6 to 0.81; 0.94 to 1.62; and 1.88 to 3.2Gb/s.

解决方案

There are two deviations from the standard Wizard generation flow that need to be taken note of when generating a wrapper for newly supported line rates:

1) In the Spartan-6 FPGA GTP Transceiver Wizard itself, when selecting a line rate, select the closest line rate from the previously supported range.

Note the proportion between the target line rate and the rate selected, and select a reference clock rate that is proportionally similar to the intended reference clock.

This ensures that allof the settings generated by the Wizard are correct for the resulting line rate, including the PLL divider settings.

2) The example UCF generated by the Wizard has timing constraints that are incorrect for the target speeds. 

Update the reference clock period constraint to match the period of the expected reference clock, and the TX/RXUSRCLK(2) constraints to be in line with the formulas in the FPGA RX and TX Interface sections of the Spartan-6 FPGA GTP Transceiver User's Guide (UG386):

https://www.xilinx.com/support/documentation/user_guides/ug386.pdf

Note: In Version 12.2 and earlier, the speed files have not been updated to allow for line rates above 3.125Gb/s. Users that require higher line rates need to use 12.3 once it is released.