Question about DDR3 Frequency !

[tengri]

Hi All, 

For our IMX6Q based custom board, we are using Alliance 4x 4Gbit memory chips. However the maximum DDR3 frequency of the chip is said to be 800MHz (DDR3-1600). When I run OpenGL applications, few boards just randomly hang. I am using boundary devices u-boot-v-2016 and kernel 4.1.15_0.2 !

https://www.alliancememory.com/wp-content/uploads/pdf/ddr3/Alliance%20Memory_DDR3_4G_AS4C256M16D3A-1... 

1. So according to the speed grade this should be only compatible with IMX6Q 400MHz (the other option being 528MHz) DDR operation right ? 

2. I performed the memory calibration for 400MHz DDR frequency and updated relevant DCD headers in u-boot source files (800mhz_4x256mx16_our.cfg).

3. However when I login and check the clock_summary in kernel, the mmdc_ch0_axi, mmdc_ch1_axi as well as gpu3d_core_sel  clock roots are still seen to be 528MHz. Please refer following link for the summary.

[Bash] Clck_Summary - Pastebin.com 

4. So if the u-boot ddr timing is set for 400MHz, shouldn't those memory control clock roots be set to 400MHz (or 396MHz) as well ? In that case which source file should be changed in the kernel ? I can see that CCM_CBCMR is the relevant register for the clock roots ! i.e. it's set to something else in arch/arm/mach-imx/ddr3_freq_imx6.S in multiple times. 

Thanks in Advance

[igorpadykov]

Hi Anuradha

1. there are no known issues with using memories with different speed grades.

Usually fast speed grades memories work fine on lower frequencies, which uses i.MX6.

2. correct memory settings do not guarantee from hanging, as it may be also caused

by power supplies, please check power requirements (like ripples) in i.MX6 System Development

User’s Guide

https://www.nxp.com/docs/en/user-guide/IMX6DQ6SDLHDG.pdf

3.4. calibration coefficients for 400MHz do not restrict usage for other frequencies,

(as if board layout is good, there is sufficient margin for operation with other frequencies),

just for test one can calibrate in 528MHz and check if issue persists.

Best regards
igor
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