Switch ARMv7 Cortex-A processor to ARM mode right before jumping to target

[Peter Robinson]

Hi Anatol,

> I’m facing an instruction set mismatch issue on ARMv7. The system uses
> a proprietary U-Boot–based bootloader (based on v2022.07) that runs in
> ARM mode and then jumps directly to my application. The application
> itself (Zephyr-based) is built in Thumb mode by default, which leads
> to problems when execution is handed off.
>
> Unfortunately, I cannot modify or rebuild the U-Boot binaries, as they
> are closed-source in this case. The only control I have is through the
> U-Boot environment (uboot_env).
>
> Given these constraints, is there any way - via U-Boot environment
> configuration - to switch the processor into Thumb mode right before
> jumping to the application?
>
> If not, are there any recommended workarounds for handling this ARM
> <=> Thumb transition when the bootloader itself cannot be modified?
>
> Thanks in advance for your help!

So you're going to need to raise