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Internal ring oscillator affect operation of MMDC?

Question asked by Norihiro Michigami on Jan 23, 2017
Latest reply on Jan 24, 2017 by Norihiro Michigami

Hello NXP team,


On i.MX6Q, we don't need accurate timing for RTC, so we left open Xtal input for RTC. 

In this configuration, we understand that the internal ring oscillator is used. 

With this configuration, we faced strange issue on i.MX6Q.  

We found that our application software performance got lowered during certain temperature of die. 

(We measured the die temperature with integrated temp sensor of i.MX6Q)

According to internal register information, the busy counter of MMDC is higher when this issue is seen.

DDR memory access itself is fine, so we don't if the high busy counter value caused this issue.

And this problem is not seen on every board we assembled. So, we did A-B/B-A test (swapping i.MX6 between known good board and the board which showed this performance issue), then, issue seems to be depending on specific i.MX6. 


After our thorough investigation on this specific i.MX6, we found out that the performance issue was completely gone, when we just added x'tal for internal RTC to our board.

According to local FAE of NXP Japan, he told us that it was possible because the refresh timer referred to the low speed clock from internal ring oscillator.  


Our question is:

1. Must we use xtal for RTC so that MMDC works stably, if internal ring oscillator caused the issue we faced?

2. Could you advise us what modules on this SoC uses the internal ring oscillator other than MMDC and RTC?



Norihiro Michigami