On Thu, Nov 13, 2014 at 11:19 PM, John Tobias john.tobias.ph@gmail.com wrote:

Hi Fabio / Stefano,

May be you could help me to get some answer regarding with calibrations value for DDR.

I have a 4 custom boards based on iMX6SL (2) Micron DDR and (2) Samsung DDR.

The boards has exact DDR footprints (like density, bus width and so on). In fact the uboot that I am using works on both DDR chips.

I re-ran the DDR tools twice for each boards, entered the same information. The tools returned different calibration values for each boards but, the two results for each boards were the same.

e.g: board1

Read DQS Gating calibration MPDGCTRL0 PHY0 (0x021b083c) = 0x412C0130 MPDGCTRL1 PHY0 (0x021b0840) = 0x01140118

Read calibration MPRDDLCTL PHY0 (0x021b0848) = 0x3E404244

Write calibration MPWRDLCTL PHY0 (0x021b0850) = 0x383C3E36

board2:

Read DQS Gating calibration MPDGCTRL0 PHY0 (0x021b083c) = 0x412C0130 MPDGCTRL1 PHY0 (0x021b0840) = 0x01140118

Read calibration MPRDDLCTL PHY0 (0x021b0848) = 0x3E3E4244

Write calibration MPWRDLCTL PHY0 (0x021b0850) = 0x383C3E36

Is there any procedures or rules of thumb you follow dealing with the calibration settings?.

Then you need to provide a mx6_mmdc_calibration structure for each board, right?

Take a look at gw_ventana_spl.c for an example on how this is done.

Regards,

Fabio Estevam

Hi John,

On 11/14/2014 03:19 AM, John Tobias wrote:

Hi Fabio / Stefano,

May be you could help me to get some answer regarding with calibrations value for DDR.

I have a 4 custom boards based on iMX6SL (2) Micron DDR and (2) Samsung DDR.

The boards has exact DDR footprints (like density, bus width and so on). In fact the uboot that I am using works on both DDR chips.

I re-ran the DDR tools twice for each boards, entered the same information. The tools returned different calibration values for each boards but, the two results for each boards were the same.

e.g: board1

Read DQS Gating calibration MPDGCTRL0 PHY0 (0x021b083c) = 0x412C0130 MPDGCTRL1 PHY0 (0x021b0840) = 0x01140118

Read calibration MPRDDLCTL PHY0 (0x021b0848) = 0x3E404244

Write calibration MPWRDLCTL PHY0 (0x021b0850) = 0x383C3E36

board2:

Read DQS Gating calibration MPDGCTRL0 PHY0 (0x021b083c) = 0x412C0130 MPDGCTRL1 PHY0 (0x021b0840) = 0x01140118

Read calibration MPRDDLCTL PHY0 (0x021b0848) = 0x3E3E4244

Write calibration MPWRDLCTL PHY0 (0x021b0850) = 0x383C3E36

Is there any procedures or rules of thumb you follow dealing with the calibration settings?.

As far as I know, the calibration values are actually settings for the delay lines, used to align data and clock signals. I can assure you that each separate imx6 chip, DDR chip, and each board are absolutely uniqie in their parameters, because there are manufacturing inaccuracies that can't be avoided. Also the ICs parameters change with temperature, and the PCB parameters (dielectric permittivity) changes with frequency. Just think about this - even 2 subsequent runs of DDR stress tester will return close, but not exactly the same calibration values.

Now, on the positive side, these inaccuracies are not that big and usually it's quite safe to just perform the calibration with the FSL DDR stress tool on one of the boards and use these fixed values for all the boards. This is very easy to be done whem DDR ICs are soldered on the PCB, and somewhat harder to do when using SO-DIMMS (but I have a customer board already that's running this way without issues). I can also confirm that I've personally seen such approach even in automotive products. What's important is to make sure there are no big changes in the manufacturing process and components revisions, and that the boards (especially DDR area) are clean from flux/finger fat.

If I remember correctly, the MMDC module has a mechanism to perform periodic fine recalibration that handles the slight fluctuations in the component parameters, while the software is running.

If you are concerned with the temperature stability of your DDR calibration, you can always do a thermal chamber tests in the full temperature range of your product, just to be sure.

Hope this helps. Kind regards, Nikolay

PS: If you need more scientific approach to justify this to someone else, you can test a representative amount of your product boards, extract all calibration values, do a chart with normal distribution of the calibration values and select the values with highest probability.