iMX6UL PLL2 Spread Spectrum

[Nitin2021]

Hi Comminity,

We intend on enabling spread spectrum modulation for iMX6UL PLL2 and we had a few queries regarding the same. 

We want to enable the Spread spectrum at a "Spread Spectrum Range" of 6MHz/12MHz/24MHz at a "Modulation Frequency" of 48KHz/60KHz. We had referred the iMX6UL Reference Manual and we were able to calculate the values to be written on to the 528MHz System PLL Spread Spectrum Registers (CCM_ANALOG_PLL_SYS_SS, CCM_ANALOG_PLL_SYS_NUM and CCM_ANALOG_PLL_SYS_DENOM ). The following are our queries for the same:

i.We are however, unaware of where the above values needs to be written in the U-Boot and Kernel of the Yocto BSP.

ii. Are there anymore configurations to be done for the same.

We had referred the following previous queries for our reference:

https://community.nxp.com/t5/i-MX-Processors/Spread-spectrum-modulation-of-i-MX6UL/td-p/533161

https://community.nxp.com/t5/i-MX-Processors/i-MX6DQ-PLL2-spread-spectrum/m-p/264342

Please provide your insights on the same.

Thanks & Regards

Nitin Nirmal

[igorpadykov · Accepted solution]

Hi Nitin

>We are however, unaware of where the above values needs to be written in the U-Boot and Kernel of the Yocto BSP.

it can be added to uboot dcd header

https://source.codeaurora.org/external/imx/uboot-imx/tree/board/freescale/mx6ul_14x14_evk/imximage.c...

Best regards
igor

[Nitin2021]

Hi Igor

Thanks a lot for the quick reply

Based on your inputs, we had added the required configuration fields on our U-Boot DCD header to configure the 528MHz System PLL Spread Spectrum Registers for a spread spectrum range of 12MHz and Modulation frequency of 48KHz. The following are the values for the 528MHz System PLL Spread Spectrum Registers according to our calculations.

CCM_ANALOG_PLL_SYS_SS - 0x05DC8006

CCM_ANALOG_PLL_SYS_DENOM - 0x00000BB8

Are there anymore changes that needs to be added for the same to take effect

We are using the iMX6UL proccessor and our DDR clock frequency is at the default value of 396MHz. Since we are configuring the spread spectrum using the System PLL which will only be run at default frequency of 528MHz, we tried re-caliberating our DDR clock frequency to 528MHz using the DDR STRESS TOOL. We then updated the corresponding register values in our U-boot .cfg file however, when we physically probed and checked for the DDR clock frequency, we found that the same did not change and was still at  396MHz.

We had referred the following previous queries and we found that the maximum specified DDR clock frequency for iMX6UL is 400MHz. The  link for the same is provided below:

https://community.nxp.com/t5/i-MX-Processors/Running-DDR3L-below-its-specified-frequency-with-iMX6UL...

We have the following queries regarding the same:

1. Can the DDR clock frequency for iMX6UL processors be re-caliberated to values over 400MHz (for 528MHz).

2. Would enabling the 528MHz System PLL have any effect if the DDR clock frequency is set to the default 396MHz or do we need to re-caliberate the same to 528MHz for the same. Is our understanding regarding the same correct

Please provide your inputs on the same. 

Thanks & Regards

Nitin Nirmal

[igorpadykov]

Hi Nitin

1. max. supported frequency is 400MHz as described in sect.4.10.2 MMDC supported DDR3/DDR3L/LPDDR2 configurations  i.MX 6UltraLite Applications Processors for Consumer Products Data Sheet

2. you should use default 396MHz and just enable System PLL spread spectrum.

Best regards
igor