B3 with different RAM chips

Tiago Marques tiagomnm at gmail.com
Sun Nov 22 14:15:07 EST 2009


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. Are you running at 400 or 533? Doesn't the datasheet
specify the appropriate timings?

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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