In order to utilize ICDI on "EK-TM4C129EXL" to program/Debug TM4C12x on custom board. Please confirm any issue with steps below:
1. Remove jumper from header JP2 such that TM4C129 on "EK-TM4C129EXL" is powered down avoiding any conflict/contention with TM4C12x of custom board (keeping resistors R8,10,11,15 & 16 as it is.)
2. Ensure that header pin EXTDBG is unconnected
3. Install the right hand pins of header X1 for the JTAG pins
4. Connect the GND from EK-TM4C129EXL to GND on the custom-board.
5. Connect the X1->TCK from EK-TM4C129EXL to TCK on the custom-board TM4C12x.
6. Connect the header pin TMS from EK-TM4C129EXL to TMS on the custom-board TM4C12x.
7. Connect the header pin TDI from EK-TM4C129EXL to TDI on the custom-board TM4C12x.
8. Connect the header pin TDO from EK-TM4C129EXL to TDO on the custom-board TM4C12x.
9. Connect the header pin RST_N from EK-TM4C129EXL to RST pin of TM4C12x on the custom-board
10. Connect the USB cable on the debug connector