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

[Jerry Van Baren <gerald.vanbaren@smiths-aerospace.com>]

Alan Bennett wrote:
> On 9/11/07, Jerry Van Baren <gerald.vanbaren@smiths-aerospace.com> wrote:
>> Alan Bennett wrote:
>>> Jerry;
>>>   This is interesting, on further examination, I see replication
>>> occurring on the 16 MB boundary.  Are you saying that this is due to a
>>> misconfiguration of the BR/OR registers?
>>> i.e. writing to 0 results in replication when reading from 01000000 /
>>> 02000000 / 03000000 etc...
>>>
>>>   Along the lines of the mtest errors.  I see 340 B of errors just
>>> running the initial mtest routines.  I'll see if I can find out what
>>> might be in that area, but of course, that's after figuring out this
>>> replication problem.
>>>
>>> mtest results:  size of memory error area:
>>>          0x00B8BDE4-0x00B8BC90=0x154
>>> Mem error @ 0x00B8BC90: found 07B8BCA0, expected 002A2F24
>>> ...
>>> Mem error @ 0x00B8BDE4: found 07FDC3D0, expected 002A2F79
>>>
>>>
>>> -Thanks again, Alan
>> Hi Alan,
>>
>> Note: I've forgotten which processor you use and whether it is SDRAM,
>> DDR, or DDR2.  In the discussion below, I'm talking about SDRAM and am
>> somewhat vague, but the concepts apply to all configurations.  DDR/DDR2
>> are simply improved ways of implementing synchronous dynamic RAM (SDRAM).
>>
>> I can think of three ways of having your memory replication problems
>> (BR/OR configuration does not appear to be one of the ways).
>>
>> 1) If your SDRAM initialization is wrong such that you set up the
>> processor's bank/page addresses to a value that doesn't match your SDRAM
>> internals, you will get replications on the boundaries of your banks/pages.
>>
>> 1a) Wrong banks per device or wrong row start address: I would expect
>> this to be around 4K-32K, depending on your SDRAM.  Not your situation.
>>
>> 1b) Wrong number of rows: Definite possibility - you need to have the
>> right number of address lines configured in your SDRAM machine
>>    (row_start_address - 1) + banks_per_device + number_of_rows
>> (note row_start_address - 1 == columns) so that they match the number of
>> address lines (memory size) of your memory.  If you have too few address
>> lines configured in your SDRAM configuration, you would create the
>> symptoms you are seeing.
>>
>> 2) If you have a hardware wiring (layout) error with a missing address
>> line, you will have have replication based on that line since the CPU
>> will toggle it appropriately but the memory won't see it.  Given the
>> multiplexed nature of SDRAM addresses, this is somewhat less likely
>> because a missing/broken address line would tend to hit both row and
>> column addresses.  However, if the missing/broken address line is only
>> used for the row address, it would match your symptoms.
>>
>> 3) If you have a fabrication problem (short/open), the affected address
>> line will generally be stuck low, stuck high, or driven by an adjacent
>> line (which is almost always another address line).  In all three cases,
>> the CPU toggles the affected address line but the memory doesn't see it,
>> causing a replication scenario.
>>
>> Since you say you have a replication on a 16MB boundary, the address
>> line that is suspect is A23 (2^24 - WARNING, I'm using the "standard"
>> bit numbering here, NOT PowerPC).  #1b or #3 are the most likely
>> problems.  For #1b, I would verify the SDRAM (DDR, I forgot what you are
>> running) configuration.
>>
>> For #3, X-ray machines for checking balls (solder quality) and VOMs for
>> checking for continuity and shorts is where I would go next.
>>
>> In parallel, I would task the hardware designer and/or layout person
>> with verifying that the address lines are connected properly, especially
>> A22, A23, A24, (and the multiplexed equiv. going to the SDRAM) and any
>> other address lines that may be adjacent to A23.
>>
>> Good luck,
>> gvb
> 
> Good news;
>   I found an error in my PSDMR and after correcting that, I'm off and
> running mtest and the replication has also disappeared.
> 
>   Thanks for your help!  BTW.  It is a 128MB SDRAM MPC8248 design with
> 2 banks of 128MB flash
> 
> -Thanks!

Very good news!  Cheap solution (#1)!  Some days you eat bear, some days 
the bear eats you.  I hear bear is very tasty.  ;-D

gvb