The following errors occur when connecting to the JTAG cable in the ChipScope tool:
ERROR: Internal Error: Failed reading JTAG Instruction Register.
ERROR - Device 0: Communication failed with device: 0
This issue is usually related to the IR length defined for non-Xilinx devices; if this is incorrect, it can prevent the IDCODE of the devices in the chain being read out incorrectly which causes problems when attempting to initialize the chain.
If this error occurs, ensure that the IR length that is being added is correct based on the BSDL file of the non-Xilinx device.