6.10 Enabling JTAG comms on the UCD3138 series
On startup, checksums tests are executed by the boot ROM code to verify the integrity of the program flash contents. If any of these tests pass, JTAG comms are disabled by the boot ROM code before control is relinquished to the firmware in program flash. We show the line of code that you need to insert in your firmware to re-enable JTAG comms. The tutorial also shows the modification available via PMBus to the IOMUX register on the UCD device to re-enable JTAG comms, of course to make this modification, the firmware needs to support PMBus.