The bits of the test_in bus have the following definitions:
- : Simulation mode. This signal can be set to 1 to accelerate initialization by reducing the value of many initialization counters.
- : Reserved. Must be set to 1’b0
- : Descramble mode disable. This signal must be set to 1 during initialization in order to disable data scrambling. You can use this bit in simulation for Gen1 and Gen2 Endpoints and Root Ports to observe descrambled data on the link. Descrambled data cannot be used in open systems because the link partner typically scrambles the data.
- [4:3]: Reserved. Must be set to 2’b01.
- : Compliance test mode. Disable/force compliance mode. When set, prevents the LTSSM from entering compliance mode. Toggling this bit controls the entry and exit from the compliance state, enabling the transmission of Gen1, Gen2 and Gen3 compliance patterns.
- : Forces entry to compliance mode when a timeout is reached in the polling.active state and not all lanes have detected their exit condition.
- : Disable low power state negotiation. Intel recommends setting this bit.
- [31:8]: Reserved. Set to all 0s.
For more information about using the test_in to debug, refer to the Knowledge Base Solution How can I observe the Hard IP for PCI Express PIPE interface signals for Arria V GZ and Stratix V devices? in the Related Links below.