SPI Bootloader Synchronization Issue

[dscdsc]

I'm following the bootloader ACK procedure outlined in AN4286, page 6.

 

The issue I'm having is that the bootloader never responds with 0x79 (ACK) or 0x1F (NACK) after the initial synchronization (Sent 0x5A, Received 0xA5).

 

Are there any issues with my understanding of the procedure? I'm assuming the dummy byte first sent by the bootloader is supposed to be used throughout the procedure?

I'm using STM32H750B-DK with erased flash memory, and proper PI0, PI1, PI2, PI3 pins for SPI2 as outlined in AN2606, page 263.

SCK is pulled down to GND with a 10k resistor, NSS is pulled down at the start of every transaction (tying it to GND as suggested in the docs seems to work worse).

Seems like a similar issue to post, but not the same Cannot get into the factory ST bootloader from AN2606 for programming over.

[TDK]

I appreciate you posting updates. I don't have any further ideas, looks like you're doing everything correctly as far as I can tell.

I have several H7 boards so maybe I'll try it out as well.

[dscdsc · Accepted solution]

Able to get to ACK by sending 0x00 instead of the initial dummy byte, but it takes 40 attempts.

[dscdsc]

Dupe.