[U-Boot] DRAM clock frequency issue

[Chris Packham]

On Fri, 1 Jun 2018, 10:42 PM Greg Maitz, <ghh19622 at gmail.com> wrote:

> Hi - I have a target Atheros 9344 board on which I have loaded U-boot
> version 1.23.2. On the reference board, the DRAM clock frequency has
> been set to 400 MHz and it works well.


Sounds like you've got a vendor bootloader. 1.23.2 isn't a version number
used by u-boot. You might get more informed support from wherever you
obtained this.

But when the same clock
> frequency is used on my target board , mtest (memory test) fails.
> However, when I reduced the clock frequency to 300 MHz, the mtest
> passes and it appears to be stable.
> The reference and target boards are alike in almost every respect.


Double check this assertion. Even if things appear similar on a schematic
the board layout is significant when it comes to ddr.

The
> DRAM specifications are the same but the manufacturer is different.
>
>  I tried setting the DRAM timing parameters on my target DRAM to be
> aligned with the numbers in the data sheet. When I load the Linux
> kernel after this, there are a variety of kernel panics seen if I
> leave it on overnight. They are OOPS messages such as "Unable to
> handle kernel paging request at virtual address", I think they may be
> related to the DRAM clock frequency setting.
>

A plug here for memtester http://pyropus.ca/software/memtester/ it's been
quite handy for excercising ram. Unfortunately it won't fix the problem,
but it will let you know when you have.

I'd like to eventually use 400 MHz clock for the DRAM clock frequency
> on my target board. If anyone has faced a similar scenario earlier,
> kindly share your tips to debug the problem.


I've used enabled 2T timing (assuming your ddr controller supports it) for
similar issues in the past. If it works it's usually an indication of some
hardware issue but it may get you through to the next board spin.