topic Re: i.MX8QXP LPDDR4 issues in high temperature in i.MX Processors

i.MX8QXP LPDDR4 issues in high temperature

jran — Tue, 24 Nov 2020 15:46:28 GMT

While doing climate testing of our i.MX8QXP product, some issues have come up.

When SoC reports temperature above +85°C we started seeing glitches on the screen, and after some time Weston and/or any running application crashes with segfault.

We are running SCFW porting kit 1.6.0 with DCD Cfg settings generated from latest v15 of DDR Configuration spreadsheet, and linux-fslc-imx 5.4.74.
CPU revision is B0. Running 2GB LPDDR4 at 1200 MHz.

We have run DDR stress test tool in +90°C surrounding temperature at 1200-1300 MHz without issues. So the memory bus itself seems stable.

What does seem to solve the issue is to select "Apply maximum de-rate timings" in the configuration tool, then the board seems to be working fine even at +95°C SoC temperature.
We tried only disabling the automatic de-rate feature, but that made no improvement. Still the same glitching and crashing, only that the board no longer booted at high temperature.

What are the drawbacks of using maximum de-rate timings? Higher current consumption?

Also, are there any settings which can be tweaked for the de-rating? Since using maximum values at all times solves the problem, I'd guess that more de-rating would also work.

We have set T_RFC_NOM_X32 to 3904 as per the SDRAM datasheet nominal tREFiab. But of course the datasheet specifies much lower values for temperature above +85°C. Shouldn't this be considered anywhere?

Could one assume that this issue will be gone when moving on to C0 silicon?

Re: i.MX8QXP LPDDR4 issues in high temperature

jran — Wed, 25 Nov 2020 08:01:30 GMT

After doing some more reading I found that the de-rating settings comes from the SDRAM, register MR4.
So there are basically no settings for this, then. It should just work.

But why doesn't it? Are there more issues with the B0 silicon than what the Errata says (states that the issue is only if *startup* temperature is high)?

And the main question remains, what are the drawbacks of using maximum refresh rate?

Re: i.MX8QXP LPDDR4 issues in high temperature

igorpadykov — Mon, 30 Nov 2020 04:06:07 GMT

Hi jran

>..Could one assume that this issue will be gone when moving on to C0 silicon?..

this is cause by rev.B0 erratum e50125 "DRAM: Controller automatic derating logic may not work as intended.."

Mask Set Errata for Mask 0N95W-B0 Silicon

It is fixed in rev.C0 as described in Mask Set Errata for Mask 0N99Z-C0 Silicon

i.MX 8X C0 Migration Guide Migrating from i.MX 8X B0 to i.MX 8X C0

Best regards
igor