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Date of registration: Jun 4th 2015

Posts: 2


Friday, June 5th 2015, 11:02am

[SOLVED] Nitrogen Max with JLinkGDBserver - Failing reads after commands to external DDR

When running JLink with a Nitrogen Max board, I have difficulties to read peripheral
registers and memory after performing the initial setup of pins, DDR memory and clocks.

I am starting JLink GDB on an Xubuntu 15.04 X64 machine with:

Source code

JLinkGDBServer -device MCIMX6Q6 -if JTAG -speed auto

The GDB client is started with

Source code


The initial setup (see appended gdbinit file) is taken from the board setup files for Nitrogen Max
in Boundary Devices U-Boot repo.

I am able to write and read all the way up to the step where I start to issue commands to the DDR through
MMDC Core Special Command Register (monitor memU32 0x021b001c=0x04088032).
After this I am no longer able to read peripheral registers.
I also notice that some write operations have been duplicated, might this be a speed issue?
I have also tested to swap enabling the clocks early/late and not using the "-speed auto" option with no

Any clues on what goes wrong? Any special tricks that must be performed?
If anyone has some info on reference iMX6Q JLinkGDBServer/GDB scripts out there that are known to work,
I would be very pleased to hear about it!
As soon as the access works as expected, I plan to load U-Boot and execute it from the gdb environment. :)
tan has attached the following files:

This post has been edited 2 times, last edit by "tan" (Jun 5th 2015, 11:35am)



Date of registration: Jun 4th 2015

Posts: 2


Monday, June 22nd 2015, 3:56pm

Problem solved :)

The described issue was caused by a duplicated DDR initialization. The first initialization was done by an existing bootloader in SPI NOR flash.
The problem can be avoided by forcing the boot mode to USB serial download.
When using the serial boot mode, the initialisation by the script is running OK and access to the DDR memory is granted.


Super Moderator

Date of registration: Dec 20th 2011

Posts: 400


Tuesday, June 23rd 2015, 11:10am

Thank you for the update in this issue. Good to hear that you are up and running now.

- Erik