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Debugging an i.MX6UL running Linux over JTAG with a J-Link

Question asked by Jay Carlson on May 24, 2018
Latest reply on May 26, 2018 by Jay Carlson

I have a custom i.MX6UL "breakout" dev board I'm bringing up that doesn't have any peripherals on it (other than RAM and uSDHC1). I've got some Linux instability issues that I'm working through, and I'm trying to attach my J-Link to the board to see where the kernel is when it hangs, as I'm getting no panic messages.


So, my question is: what's the right way to attach a J-Link to a running i.MX6UL to debug the Linux kernel?


I followed this post, which tells you to disable the 'clock off' wait state and use the -noir and -noreset options with the J-Link. Unfortunately, when I try starting my debug session with:

./JLinkGDBServer -if JTAG -endian little -device MCIMX6G3 -select USB -noir -noreset

the J-Link resets the MPU immediately. I thought maybe I could attach to it during U-Boot, and then start debugging once I was in Linux, but the connection gets closed between the U-Boot and Linux start-up phase.


I'm using JLink software V6.32c. My board doesn't use the sai2 interface, so there shouldn't be the widely-reported JTAG pin-muxing issue that others have struggled with.