B3 with different RAM chips

[Tiago Marques]

On Sun, Nov 22, 2009 at 8:01 PM, Mitch Bradley <wmb at laptop.org> wrote:
> 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.

Ok, I was rather confused when I read:

"I switched the timing to CAS latency 4 (from 3), which ** should meet
** specs for this chip."

And was finding rather odd that you didn't had access to specified timings.

Best regards,
Tiago Marques

>
>> 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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>