[Letux-kernel] 2GB vs. 4GB Pyra RAM tests

Tony Lindgren tony at atomide.com
Thu Aug 17 16:36:03 CEST 2017

* Michael Mrozek <EvilDragon at openpandora.org> [170817 06:38]:
> Okay, got some replies from my distributor.
> The RAM is tested to work with 1.35V.
> He's got some ideas though:
> * The timings are DIFFERENT when running with 400MHz (DDR3-800) and
> often not in the datasheets. If we're running at that speed, we might
> have to adjust those. The timings can be found on the JEDEC
> Specification on page 170 and later (I'll send the document to you via
> Mail, as that's not public).
> * Also, if we're running at low speed, the DLL can interfere with the
> RAM. This can be disabled via Mode-Register (might be something we can
> try).

Setting bit 21 to disable ddr3 dll together with termination set to 2
helps with the issue I was seeing where u-boot is having hard time
starting. So I'm currently using config value of 0x62a51b3a.

At 1.35V, kernel still keeps hanging all the time during boot so
no changes there.

> * As it's dual rank, it could be the layout needs to be adjusted (as it
> has more load on the lines). However, then I guess it would run
> unstable at 1.4V as well, wouldn't it?
> Anyways, that DLL and the timings are our best guess for now, I think.

I believe we're already using jedec timings. And they work
with 1.42V and above.. I don't quite see how the timings
would be affected by the voltage?



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