NRF52840 QSPI IFTIMING Problem

[Bing]

Dear,

We are working on our custom boards to develop a watch product which need external flash memory connected by QSPI interface. In this product, the UI images and font bitmaps store in the external memory. We found the screen of some watch samples display noise content(the data source comes from the external flash memory).  We tried to change IFTIMING register value, and we found the problem watches display problem been fixed. But some other watches no need to change the default value of IFTIMING (the default whole register value 0x00000200). The proportion of problem products is about 6%. 

We want to know why the problem products can fix this issue by change IFTIMING register while some most of the product (the other 96%) no need to change this register. And whether the IFTIMING register change would lead other unknown issues.

The following is my understanding about IFTIMING, seems the default value is not fit the the CLOCK mode=0 (CPOL=0, CPHA=0) with the QSPI clock=32MHz.

Our the external flash memory is XT25F128BWOIGT.

[haakonsh]

We want to know why the problem products can fix this issue by change IFTIMING register while some most of the product (the other 96%) no need to change this register. And whether the IFTIMING register change would lead other unknown issues.

I don't know why you see this issue exactly. I suggest we do a HW review to see if there is any obvious signal integrity issues in the design. 
We don't know if changing the timings will lead to unknow problems in your design. 

If you change the IFTIMING of the 'good' devices, does it have a negative impact, or do they continue to function as intended?

[you can123]

We tested a batch of "bad" devices and changed the IFTIMING register to 0x100. Most of the read and write data damage can be recovered, but some of them cannot be solved, but these can be solved by reducing the frequency to 16MHZ.