[Skiboot] DDR4 Calibration and address inversion

Alexandre Ghiti aghiti at upmem.com
Thu Jun 27 19:54:05 AEST 2019

Hi everyone,

We are currently testing our RDIMM in a Talos server which runs custom
hostboot/skiboot from RaptorCS team.
Our RDIMM (single-rank) is 'rejected' during calibration as half the DRAMs
fail the DQS alignment step. We know, for some internal reasons, that if
this step tries to access the DRAMs with BG1=1, it will fail, which will
happen if address inversion is enabled (see RCD jedec JESD82-31 section
2.9): so half the failing DRAMs would represent the side-b.

I did not succeed to disable address inversion, certainly because the piece
of HW that does the actual calibration supposes the address inversion is
activated and then invert the corresponding bits to prevent RCD inversion.

My questions are:
- Is the CCS responsible for executing the calibrations ?
- Is there anyway to modify its behaviour ? (I don't think the calibration
steps are purely HW...)

Thanks for your answers, and if this is not the place to discuss such
things, please do not hesitate to say so.


*Alexandre Ghiti*
*Software Engineer*
Port : +33 687 605 894
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