B3 with different RAM chips

[Mitch Bradley]

Tiago Marques wrote:
> Hi,
>
> The hardware page for the XO 1.5 doesn't show the clockspeed of the
> RAM chips used. CAS 3 looks like very aggressive timings for cheap
> DDR2 chips. 

CL3 is in spec for the chips that we were using but not for a new chip 
that we might start using.

> Are you running at 400 or 533? 

400
> Doesn't the datasheet specify the appropriate timings?
>   

Of course it does.  The jumper is to tell which timing set to use, 
depending on which chips are populated.

> Best regards
>
> On Fri, Nov 20, 2009 at 8:21 PM, John Watlington <wad at laptop.org> wrote:
>   
>> I suggest that we dedicate the unused
>> memory ID 0 jumper (GPIO9) to indicate that
>> this DRAM is present.
>>
>> Thanks for reminding me, as Richard and I
>> wanted to add another jumper since we've used
>> them all up.
>>
>> wad
>>
>> On Nov 20, 2009, at 2:51 AM, Mitch Bradley wrote:
>>
>>     
>>> I have a B3 with 1 GiB of memory, using Samsung K4T1G084QE RAM chips
>>> which have slightly different timing than the chips we were using.
>>>
>>> Using the old timings, it booted Open Firmware and appeared to
>>> work, but
>>> memtest quickly elicited errors - it started showing them after
>>> about 20
>>> seconds, during test #2, moving inversions with a constant pattern.
>>>
>>> I switched the timing to CAS latency 4 (from 3), which should meet
>>> specs
>>> for this chip.  memtest has been running for 7 minutes with no errors.
>>> I'll leave it running overnight.
>>>
>>> If we are to use this chip, we'll need a way to identify it - perhaps
>>> one of the memory ID straps - unless we want to run the other chips at
>>> CL4 too.
>>>
>>> CL4 has little or no effect on the memcpy speed, but it would slow
>>> down
>>> random reads to a small extent.
>>>       
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