Configuration Readback of the PCIe Gen 3 Frames result in incorrect data being read back.
This occurs for designs where the PCIe Gen 3 block is included, but there is no DRP port instantiated.
These frames always read back as all '0's regardless of programming data. This occurs for all Configuration Readback interfaces including ICAP, SelectMap, and JTAG.
This can affect applications which use Configuration Readback, such as scrubbing or iMPACT Verify.
You might see messages in iMPACT similar to the following:
"'4': Verifying device...INFO:iMPACT:2495 - Readback Size is XXXXXXXXXX.
INFO:iMPACT:396 - Readback to map unsuccessful.
INFO:iMPACT:395 - The number of difference is X
'4': Verification terminated."
To work around this issue, you should instantiate the PCIe DRP interface as part of your PCI3 Gen 3 block.
To enable the instantiation of the DRP port in your wrapper, select the check box on Page 12 of the CORE Generator options.
Instantiating the DRP enables masking of the DRP frames.
The masking used by iMPACT for Verify will include the PCIe DRP bits, therefore, Verify will operate correctly on the rest of the device.
For Readback CRC users, the DRP memory spaces are masked automatically by this feature, so this issue will have no effect.
For users implementing their own Readback schemes, this should be accounted for by skipping these frames, or ignoring the data read back.