AR# 47643: 13.x Spartan-6 - Post Config CRC error is always flagged when BitGen generated Readback signature is used
13.x Spartan-6 - Post Config CRC error is always flagged when BitGen generated Readback signature is used
Spartan-6 Post Configuration CRC checks will fail if the BitGen generated Readback signature is used, which happens immediately after configuration. This is default behavior unless the signature generated after the first readback is selected.
To work around this issue, you need to specify the signature as the value generated on the first readback of the device by the Post Configuration CRC logic. To do that, add the following constraint to your UCF file:
Config POST_CRC_SOURCE = FIRST_READBACK;
The design will need to be reimplemented from NGDBuild.