The GTX transceiver has very specific reset requirements as described in the 7 Series FPGAs GTX/GTH Transceivers User Guide (UG476). The GTX transceiver requires careful coordination of PLL resets, GTX transceiver resets (gttxreset and gtrxreset), dynamic changes of some GTX transceiver ports including the width of the txdata and rxdata ports, and dynamic changes of GTX transceiver attributes through the DRP. Without proper coordination of all of these events, it is possible for the GTX to fall into a state in which it does not function properly, a situation from which the only possible recovery is to reconfigure the FPGA. The control module supplied with this application note enforces all of these requirements to ensure proper operation of the GTX transceiver.
The user application should never directly control the GTX inputs gttxreset and gtrxreset. To ensure proper operation of the GTX transceiver, these GTX transceiver inputs must only be controlled by the SDI control module. The user application can request GTX resets using the various reset inputs of the control module. These reset requests are serviced at the next appropriate time by the control module, coordinating the resets with other GTX transceiver actions so that they do not interfere.