Inner workings of XIP

[pellepl]

Hi,

I have some questions regarding QSPI flash and XIP on the nrf52840. We are exploring the possibility to use this feature by storing graphical content on the external SPI flash to be displayed on an OLED. Rather than fetching instructions, we would like to treat it as a memory mapped read-only data flash.

* Does the 52840 have any internal cache when it comes to reading SPI flash over XIP?

* If so, is that cache only an instruction cache rather than a data-and-instruction cache? Or is there a specific D-cache?

* If there is a data cache, what is the granularity and how big are its page(s)?

Cheers / Peter

[Simonr]

Hi Peter

I have had to create an internal ticket on this, as we need to speak with some of the devs on this one to confirm. It might take a few days to get back to you here, but I hope to get back to you next week.

Best regards,

Simon

[Simonr]

Hi again Peter

I'm afraid it's taking some time to get a proper reply to these questions. We have an internal ticket ongoing, and I'm still waiting for a reply from the internal experts. I will get back to you next week with another update (hopefully an answer to your questions).

Best regards,

Simon

[pellepl]

Hi Simon,

thanks for the update. No stress! Have a nice weekend!

Cheers / Peter

[Simonr]

Hi again Peter

I got an update today. There is no cache when reading external flashes with XIP, so the other questions are not applicable I guess. I'm being told this is possible to do yourself in the driver though.

Best regards,

Simon

[pellepl]

Hi Simon,

thanks! That's what I observe here also. 

Cheers / Peter