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Strange CCM_CGR Behavior of IMX6

Question asked by Anuradha Ranasinghe on Sep 11, 2017
Latest reply on Nov 13, 2017 by Anuradha Ranasinghe

Hi All,


I've developed few custom boards based around IMX6Q processor and ran into a strange problem when getting the board up !


1. First the board cannot pass DDR_Stress_Test (V2.7) for calibration and always ends up reporting a DCD_Write_Failed error (MR value - 0004, DCD Verification un-ticked). But after tweaking a bit I found out that the issue was caused by CCM_CGRx register values. The initial DDR script is meant to write reset values to those registers when DDR calibration starts (via OTG, Boot mode switches) :


setmem /32 0x020c4068 = 0xffffffff
setmem /32 0x020c406c = 0xffffffff
setmem /32 0x020c4070 = 0xffffffff
setmem /32 0x020c4074 = 0xffffffff
setmem /32 0x020c4078 = 0xffffffff
setmem /32 0x020c407c = 0xffffffff
setmem /32 0x020c4080 = 0xffffffff  // CCM_CCGR6
setmem /32 0x020c4084 = 0xffffffff


For some reason, the highlighted register write cannot be performed and this seemed to be the issue for DCD_Write_Failed. After commenting this and also after lowering the ARM_Speed I was able to do the calibration. However even manual write to CCM_CCGR6 through Stress_Tester is not successful. This can be performed in some of the Sabre Reference boards though ! But when reading the address in Stress_Tester, it gives the value of 0xFFFF0003 ! The DDR calibration result is shown below (5th Run) :

[Bash] DDR_Calibration_Arm_Speed_800MHz - 


2. After updating the u-boot with above calibrated values, I successfully burnt the serial flash and got the board to boot, but at some point of the boot process, kernel starts to hang giving a kernel panic. I am using Yocto Krogoth version and kernel 4.1.15 ! The panic message is reproducible :

[Bash] Kernel Panic -  (Showing two instances of kernel panic)  


3. The external crystal oscillator generates 24MHz for XTAL frequency. 


So does this look like an issue of clocking of the system ? Why accessing CCM_CCGR6 is restricted, although its address is valid under serial mode DCD address range ? Further could this be due to a faulty chip ?


Thanks in Advance