Hello, I have two PCB from multimedia display both are working, physically hardware is the same but have different code flash, I want to update one of them, I readed out both code flash, but if write new flash it do not work, I think that problem is with checksum, how this MCU checking checksum? What is the way to solve this issue?
I'm not sure if we can help with this. There are no features like secure boot on this device, there's nothing what would protect the code. The only feature is censorship but it is obviously not enabled if you can read and program the flash.
Checksum or verification of programmed code in general can be performed by flash programmer. Not sure what kind of tools you have.