DFU mode for STM32N6

[flexiglass]

Hello,

I'm reading the article on "How to create an STM32N6 FSBL load and run" and have a couple of questions about DFU implementation on the STM32N6:

1. Is DFU possible with the application as part of the FSBL?

2. Is there an example on how to implement DFU for when the application is part of the FSBL and also where the application is separate from the FSBL?

https://community.st.com/t5/stm32-mcus/how-to-create-an-stm32n6-fsbl-load-and-run/ta-p/768206

I'm using the stm32n6570-dk eval board.

Thanks!

[alister]

Haven't developed any STM32N6 yet, but here are some thoughts.

RM0486 Rev2 section 9.1.2 mentions USB serial boot.

IDK how a FSBL or App would start a USB serial boot under software control. Probably possible.

Implementing yourself within the FSBL should be feasible...

1. The boot ROM loads the FSBL binary to 0x34180400 in AXISRAM2 and limits its size to 511 KB, i.e. to the end of AXISRAM2.
2. From boot, AXISRAM1 and AXISRAM2 are enabled. AXISRAM1 below 0x34064000 is occupied by ITCM, DTCM and FLEXRAM. But the remaining 624 KB of AXISRAM1 and the lower 512 KB of AXISRAM2 may be sufficient for your data and any additional code. If not, the FSBL must enable additional SRAMs.
3. Finally, any additional code (i.e. over and above the 511 KB max the boot ROM loaded), the FSBL would load from an external memory, i.e. as a second-stage-FSBL, then execute, similar as how it executes an App.

[flexiglass]

Thank you for the suggestion! I dug a bit more into STM32N6 capabilities via CubeMX configurator and saw DFU class is supported via USBX middleware but since that is part of Azure RTOS I am not clear if I can mix and match. i.e.: have DFU support in the FSBL so I can just update FW through USB and run the App in bare-metal.