The device is default to shift out ID CODE when power on. To use JTAG Chain Debugger to do this, set Command is Scan Data Register and Tap State is default on End scan in RTI state. For the first power on, the JTAG can alway successfully shift out the ID CODE. But after a power cycle, It can't shift out the correct IDCODE.
The TMS pin is low while use End scan in RTI state. And if the cable doesn\'t reset, it will not release TMS and remains low. In such case, the pull up resistor is not functional after a device power cycle. TMS is low and cause an unkown JTAG instruction state. Reshift IDCODE instruction, the IDCODE can be read out again.