What's the usage of BL31 for SRAM for S32G399A?

[cranes]

Hello,

In TF-A for NXP S32G399A-RDB3, the images for bl31 to run in both SRAM and DRAM are generated in the release folder. But what's loaded by bl2 is only the bl31 version of running in DRAM. Why both images are generated then? 

I heard that bl31 for SRAM might be called directly by BootROM in other boot path and it is built in fip.bin and written to SD card together with bl31 for DRAM when flashing fip.bin. Is it true?

Thanks!

Crane

[chenyin_h]

Hello, @cranes 

Thanks for your post.

BSP code varies within the different versions, may I know which version BSP you are referring to?

BR

Chenyin

[cranes]

Thank you for your reply.

Here is the version I am using:

On branch release/bsp44.0-2.10.14

Thanks!

Crane

[chenyin_h]

Hello, @cranes 

Thanks for your confirmation.

1. Currently, at least based on BSP44, the BL31 is loaded by BL2 in DDR, at a statically-defined address.  

2. BL31SRAM is also enabled for the images on emulator.

3. Currently, there is no other available information that could be shared publicly on this feature in the BSP, I suggest checking the release notes of the BSP release for major features changes.

Apologize for your inconvenience.

BR

Chenyin

[cranes]

Hello,

You mean the documents in the red box as in below picture, right?

The below statement implies that BL31SRAM image does exist, right? 

Then the question is, what is it used for?

I find this post https://community.nxp.com/t5/S32G/quot-ATF-quot-quot-My-bootloader-NOT-U-Boot-quot-combination/m-p/1... for another processor of S32G2 series. I suspect it is the same for S32G399A or for other purpose as you said for the images on emulator. Appreciate if you help get it clear.

Thanks!

Crane

[chenyin_h]

Hello, @cranes 

Thanks for your reply.

Yes, it is existed, and could be found from the build directory once built the TFA

1. It is not described in BSP UM and related public document, so there is not formal description for it.

2. I have gone through the code carefully, by reviewing the code, the bl31sram related implementation is currently only used during system standby, to implement necessary configuration for the whole operation.

BR

Chenyin 

[cranes · Accepted solution]

Thank you for your reply.

Ok, it looks like it is still needed and might be put in fip.bin together with the image of bl31 for dram when TF-A is built so as to be stored in SD card.

Regards,

Crane