[U-Boot] PowerPC 405EX Hynix DDR DRAM Fails

[Steve Miller]

We have several designs that use the AMCC 405EX processor with a 200 SO-DIMM.  We use these SO-DIMMs to allow memory upgrades and because we can buy memory modules cheaper than the individual memory ICs.    The 405EX is only X32 interface so, we hard-code the memory size parameters in the header file and do not use the SPD data.

The designs work fine with modules built using Micron or Samsung DRAM.  We specified a Crucial part number and everything was great.  Then a shipment of Crucial modules arrived with the same manufacturer's part number, but populated with Hynix or SKHynix instead of the usual Micron parts.   The SKHynix based modules will not even boot.  The Hynix based modules will boot, but running a memory test after booting will either show byte wide fails or the processor will just lock up.

Our U-Boot source was from 2011, so I tried a tarball from late 2013 with the same fails.   I can find nothing wrong in the header file defining our board.   The Samsung and Micron modules run without any issues.   Our header file was based on the kilaeua board and I did find that it was turning on ODT for both writes and reads.  The Hynix and SKHynix would fail to calibrate at that setting.  When I changed to just ODT for writes as the AMCC User's Guide recommends, then the Hynix parts would calibrate.

If I take the Hynix modules and put them into a Canyonlands development board, they boot up fine.  Running the same mem test in the Canyonlands board that fails with Hynix on our boards and it passes fine there as well.

The main difference that I can see is that the 405EX is single-ended DQS only and the 460 on the Canyonlands is differential DQS.  The modules are PC2-5300 and rated at 667MHZ CL5.  We are running 400MHZ data at CL4 on the 405EX.   The Canyonlands board is running 400MHZ data at CL3.

Was anyone seen issues with Hynix parts running single-ended DQS?    The unused DQS~ nets are tied to ground with 1K ohm resistors.

Any hints on what to try next?

Is it possible to bump or alter the Data and DQS timings from a U-Boot prompt?   This would tell me whether I am just on the edge of the windows and not centered on it.

Thanks for any suggestions.

----- Steve