We assert nConfig to cause the FPGA to reload (for 1 second). After several attempts, the FPGA continually asserts nStatus, and is not visible on JTAG. The prevalence of this seems to change between builds. We can usually get through 30 cycles of proper boot up before we start seeing issues. This is obviously a contrived test case, but we where seeing this behavior occasionally during normal operation.
What would cause nStatus to stay asserted and the FPGA to not be able to be detected on JTAG? There is nothing in any datasheet that describes any condition where nStatus would stay asserted indefinitely.
- Configuration Fail
Are you performing Active Serial Programming? If yes, then I suspect that it is stuck in Active Serial Programming where it is not releasing the JTAG configuration mode.