AM2434: AM243x Secure Boot (SBL OSPI) – 256KB Decryption Limit vs Total MSRAM

Hello,

while working with Secure Boot on the AM243x-LP, I came across the following limitation described in the TI documentation:

https://software-dl.ti.com/mcu-plus-sdk/esd/AM243X/latest/exports/docs/api_guide_am243x/SECURE_BOOT.html

In the section related to SBL OSPI secure boot, it is mentioned that:

Decryption of application images larger than 256 KB is not possible due to the limitation that only 256 KB of MSRAM is available for temporary storage during decryption. This is because the image must be copied from flash to RAM before decryption, as flash is not directly writable.

My Questions

The AM243x device provides ~2 MB of internal MSRAM in total.

1. Is the 256 KB limitation strictly related to the default SBL memory layout?

   • Would it be possible to increase the temporary decryption buffer by adjusting the memory usage (e.g., MSRAM minus SBL reserved memory)?

2. Or is this limitation fundamentally imposed by the HSM/SBL implementation, making it non-configurable?

3. Does this 256 KB limitation apply only to SBL-related image handling, or does it also affect firmware / application images in general during secure boot?

Context

I am working with multicore application images, which can easily exceed 256 KB. I would like to understand whether this is:

• a strict architectural limitation, or
• a software/configuration constraint that can be worked around

This would help decide on strategies such as image partitioning or SBL modification.

Thanks in advance for your clarification!

Best regards,
Martin