[U-Boot] Special memory test Question

[Martin Jarman]

----- Original Message ----- 
From: "Haavard Skinnemoen" <haavard.skinnemoen at atmel.com>
To: "Martin Jarman" <mjarman at cabledoc.co.uk>
Cc: <u-boot at lists.denx.de>
Sent: Friday, October 10, 2008 12:43 PM
Subject: Re: [U-Boot] Special memory test Question


> Haavard Skinnemoen <haavard.skinnemoen at atmel.com> wrote:
>> to start at physical address zero and scribble over the entire physical
>> address range of the processor until it eventually tries to access an
>> invalid physical address and gets a bus error exception.
>
> Actually, that's wrong. It won't scribble over anything since it only
> does reads. But it will access an invalid address and get a bus error
> exception eventually.
>
>> Nope, it's a user error. Try running this command instead:
>>
>> loop.b 10400000 4
>>
>> It's been running on my board for several minutes without crashing.
>
> Btw, that command won't actually test the SDRAM since do_mem_loop()
> accesses cacheable memory. The first access will load the data into the
> dcache, and subsequent accesses will simply read it from the dcache and
> not cause any memory accesses.
>
> What is this command supposed to test anyway? It's highly unlikely that
> it will find any SDRAM problems by simply reading an address without
> checking the result...
>
> Haavard

Thank you for your replies, and I accept my 'user error' (head hung in
shame) and can confirm the test appears to run correctly when called with
the proper arguments.  I note Wolfgang has answered your question about what
the test is for.

best regards
Martin Jarman