[U-Boot-Users] best way to debug memory address problems?

[David Hawkins <dwh@ovro.caltech.edu>]

Hi Alan,

> Help;  I'm trying to figure out if these errors are hardware or
> software.  And of course, this is our first ppc/uboot system, so I'm
> still stepping through a lot of learning as I go.
> 
> I'm supposed to have a memory region from 0 to 7fff_ffff assigned to
> our 128MB memory.  However, I run into several issues when trying to
> run mtest.  I end up with an large sections  mis-behaving.  I don't
> see any conflicts in the BRx registers, and I believe my OR1 is set up
> properly, so I'm not sure how to proceed.

First thing would be to start with an oscilloscope.

I'm going to have to do this in a week or two.

Is your memory in a module, or is it directly soldered?
Is the memory SDRAM, DDR, DDR2, etc.?

Regardless of the memory type, use a scope to look
at the waveforms, relative timing of clock and data,
and compare the measurements to the data sheet.

The memory controllers have lots of options with
regards to drive strength, and timing, so those need
to be customized to a specific board. Chips such
as DDR also have internal registers for configuring
drive strength.

For example, on the MPC8349EA-MDS board, they use a
DDR DIMM module, and require a termination regulator.
On my design, the DDR memory will be on the board,
and space was a problem, so we simulated 2.5V DDR without
a 1.25V termination regulator. The system works in theory :)
But I know I will be scoping things out and messing with
the drive strength registers using the BDI2000 to talk
to the board before I even attempt to run a memory
test, let alone attempt to boot from Flash.

Cheers,
Dave