I am having a very strange issue with JTAG debugging and my embedded linux build. Up to and including Linux 2.5.35.9, I have been able to start the JLink JTAG debugger and kernel debug using remote GDB while linux was running.

Withe 2.6.36 and later, I can no longer debug. The gdb server can break and read jtag data during boot, up to point where udev runs and I get the console prompt. After this point, I get 0x00000000 CPU ID (the TDO line is not returning data). A reboot restores JTAG access.

I did a diff of the 2.6.35.9 and 2.6.36 kernels, but nothing stood out as being the cause, and I have been having a h*ll of a time trying to get processor state while in the linux code itself. I have not found any information regarding this issue, and I don't believe I am the first one to see it.

Does anybody have any ideas, seen, and/or fixed this issue on a later kernel build? I am getting close to my wits end on this issue.

george najarian
najay engineering, inc