U-boot - DDR calibration - multiple DDR references

[aebischerquenti]

Hi everyone,

I am running a custom board based on the riotboard (imx6Solo - 2x512 MB = 1GB DDR3), and I have several questions regarding DDR calibration, and how to handle multiple versions/references of DDR during the lifespan of the product.

1) What does DDR calibration values depends on ? Does it solely depends on the traces connecting the DDR chip to the imx6, or does it also depends on the DDR chip itself ? I ran some tests with different DDR references, and the results were roughly the same which suggests it doesn't depends on the DDR chip, but I can't deduct anything from a single test..

2) Correct me if I'm wrong, but at the start, the DDR is initialized with values read from the DCD table located in the first 4KB of the U-boot binary. What I'd like to know is, would it be possible to support multiple DDR calibration values to accommodate for multiple DDR versions/references inside the DCD table ? The correct values would be picked by eg. a conditional check on a GPIO ? Does it seem possible or not ?

Thanks for reading me,

Quentin

[igorpadykov]

Hi Quentin

- right, DDR calibration values mainly depend on traces length

-right, DDR is initialized with values read from the DCD.

Conditional check can not be implemented in dcd header, one can try to use

plugin option, please check Boot Chapter of Reference Manual

Best regards
igor
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[aebischerquenti]

Hi Igor,

Thank you for your answer

- OK, if DDR calibration values mainly depend on traces length, does that mean I can calibrate once and safely keep the same calibration values for multiple versions/references of DDR ?

- OK, thank you for the confirmation. I've seen that U-boot has a feature called SPL which can perform DDR calibration at the start of the product, but I've seen it used only on MX6Q products so far (like sabresd for instance). Is it possible to activate it on imx6Solo too ? Also where is the SPL loaded, in the OCRAM of imx6 ? Is it using the plugin method you mentioned in your post ?

Thank you for reading me,

Quentin

[igorpadykov · Accepted solution]

Hi Quentin

- right, one can calibrate once 

- SPL is not nxp product, one can post questions on its details on

uboot mail list:

U-Boot Info Page 

I think it uses OCRAM and can be used with imx6Solo too

Best regards
igor

[aebischerquenti]

OK thank you Igor !

Best regards

Quentin