topic Re: iMX8M DDR Tools Impedance Values in i.MX Processors

iMX8M DDR Tools Impedance Values

DavidKondrad — Tue, 23 Feb 2021 14:42:21 GMT

Greetings,

We are using the DDR Tools 3.10 and RPA v25 to tune a custom board with LPDDR4.

It appears that changing the impedance values in the RPA does seem to have an effect on the training script that is loaded; however, we do not see any changes in the "lpddr4_timing.c" file.

The values we are changing are:

ddrparam set	ATxImpedance	40
ddrparam set	ODTImpedance	40
ddrparam set	TxImpedance	34

Is this a bug or are those values only used by the DDR tool?

Regards,

David

Re: iMX8M DDR Tools Impedance Values

nxf63675 — Wed, 24 Feb 2021 23:00:05 GMT

Hi DavidKondrad,

We always change ODTImpedance/TxImpedance/ATxImpedance to fine tune the timing if there is PCB layout issue. So probably the values that you give to the programming aid have minimum changes on the timing.

Regards,

Israel H.

Re: iMX8M DDR Tools Impedance Values

DavidKondrad — Thu, 25 Feb 2021 14:49:25 GMT

HI,

Yes, of course, but I believe you misunderstand the issue.

Changes, even by large values, to those fields in the RPA (and subsequently the script used by the DDR tool) result in the exact same register programming output in lpddr4_timing.c. The files are completely identical therefore there's no way to adjust for layout issues. I would have expected that these adjustments would be carried over somehow to the configuration parameters.

I guess a better question would be:

what is the script command that accepts those impedance values actually doing?

Since the tool is closed source and the IMX8MDQLQRM is filled with "see PHY DATABOOK" references, we're flying blind here.

Regards,

David

Re: iMX8M DDR Tools Impedance Values

nxf63675 — Mon, 01 Mar 2021 23:14:52 GMT

Hi DavidKondrad,

Ok as you are saying this is not normal behavior, please attach the files that you are using, I will try from our part different configurations and see if this works, and if we still have this issue I will ask the designer of the tool why this is happening.

Regards,

Israel H.