STM32U535 blank device first flash using DFU

[phma]

Hi, 

I designed a board with a STM32U535 that connects to a USB host. 

I wanted to perform my production programming by doing the first flash over USB, without any test jig to pull-up/down any pin.

But I've just realized in AN2606, that, from my understanding:

- The U535 devices uses Pattern 12 to enter the bootloader

- The pattern 12 doesn't have "main flash empty" condition like most other patterns/families.

In this pattern 12, I see lots of conditions that I don't really understand (especially the ones with NSBOOTADD0, reference that is not documented anywhere else in this document).

Is there a way to enter the bootloader by using only the USB connection, without actively forcing BOOT0 to 1 ?

[TDK · Accepted solution]

> Is there a way to enter the bootloader by using only the USB connection, without actively forcing BOOT0 to 1 ?

On a brand new chip, no. You'll need either ST-Link (SWD) or BOOT0 control to enter the bootloader as far as I can tell.

> In this pattern 12, I see lots of conditions that I don't really understand (especially the ones with NSBOOTADD0, reference that is not documented anywhere else in this document).

These refer to option bytes which will be listed in the reference manual. To program option bytes, you will need to use the ST-Link connection, which is what you're trying to avoid so that doesn't really help.

If you have control over your code, you can jump to the bootloader in response to some input.

How to jump to system bootloader from application ... - STMicroelectronics Community