Question about removal of three-slot mode for Encrypted XIP in MCUboot

[mastupristi]

Hello,

while testing the MCUboot fork from NXP, I noticed that in the September preview release a useful feature has been removed.
Specifically, I am referring to the support for three-slot mode with Encrypted XIP (two staging slots + one execution slot, used to enable revert).

I saw this commit:
7c455cf2d 

with the message:

[MCUX-80671] Encrypted XIP: remove customization for three slot mode

Could you please explain why this functionality was removed?

• Is it considered deprecated or no longer supported?
• Are there plans to reintroduce it, or should we adapt our designs to use only two slots in case of encrypted XIP?
• Was this related to technical limitations, or more to simplify the codebase?

This feature was quite valuable for our use case, and understanding the rationale behind its removal will help us plan the next steps.

Thank you in advance for your clarification.

best regards

Max

[EdwinHz]

Hi @mastupristi,

I will investigate this topic internally. Could you please provide the MCU that you are currently using?

[mastupristi]

Hi @EdwinHz 

i'm using RT1021

regards

Max

[EdwinHz · Accepted solution]

Hi @mastupristi,

Three slot mode was a modification of the MCUboot code to support the revert mechanism (known from SWAP/DIRECT-XIP mode) in Encrypted XIP mode. However, on some devices, it's possible to implement DIRECT-XIP with flash remap and Encrypted XIP, so three slot mode doesn't make sense there. Additionally, due to the custom modification, it was difficult to maintain with newer MCUboot updates from the community, plus there were concerns about eventual certification, etc.

We are not planning to reintroduce it again.

BR,
Edwin.