N6 App OTA via UART, DFU or otherwise - not working for app image

[alnyland]

We are trying to do a firmware upgrade via UART to the N6 from another MCU, and having trouble getting it working. We do not have a USB host stack on that MCU so we're unable to use USB DFU.

I've successfully been able to transfer and start the FSBL to the N6, but am unable to transfer the app image. Another detail is that our app image is ~540KB, so a bit too big to fit in the RAM buffer. Even a smaller sample image isn't able to work.

Before I try a different bootloader or custom option, I just wanted to see if anyone else has had success doing this or if there is something I'm missing. Thanks.

[Mikk Leini]

N6 Boot ROM serial download is minimalistic - it downloads FSBL (or anything that is sent over) into AXISRAM2, but it does not write external Flash. After you send start/go command, FSBL gets validated and executed once. After reset it's gone. I've tried it with USB, not UART, but they have similar commands.

Unless you want to make FSBL your application, squeeze it into 511 KB and have a function to self-program itself into Flash, I guess you have to implement custom bootloader or use ST example bootloaders.