NUCLEO-F446RE board firmware burning.

[FWu.3]

NUCLEO-F446RE board has 2 MCU. One is on the upper side(STM32F103CBT6) and the other one is on the downside (STM32F446RET6U).

 When we burn the firmware code, the code comes from DP/DM and goes to the upper one(STM32F103CBT6). Afterward, the upper one(STM32F103CBT6) transmits the data via SWD to the downside one(STM32F446RET6U).

What is the purpose of the upper one(STM32F103CBT6)? Is the purpose to deal with the data from DP/DM to SWD? Is it an MCU to debug or something else?

Can I directly burn the code to the downside one(STM32F446RET6U) only via DP/DM without going through the upper one(STM32F103CBT6)?

Thanks

[MM..1]

Direct burn is explained in AN2606.

SWD as you say is debug interface on any STM and need upper converter named ST-LINK vX.

[TDK]

> What is the purpose of the upper one(STM32F103CBT6)? Is the purpose to deal with the data from DP/DM to SWD?

The top chip is the on-board ST-Link debugger. In addition to programming the chip, it makes debugging significantly easier/faster.

> Can I directly burn the code to the downside one(STM32F446RET6U) only via DP/DM without going through the upper one(STM32F103CBT6)?

Yes, if you have a debugger. Or if you go into bootloader mode and use one of the supported interfaces in AN2606.

[S.Ma]

You can directly write the target MCU, using biot pin and bootloaderd, for example using an usb to uart ftdi adapter

[FWu.3]

I’m curious about the firmware burning between USB(DP/DM) and the MCU.

A software “Betaflight�? is a tool to burn firmware to MCU, but it only uses USB(DP/DM) to MCU USB(DP/DM) directly. However, it seems like entering DFU(boot loader mode?) while burning firmware.

Are they different? The firmware from Betaflight and the firmware from IDE. If we ignore debugging part, can we directly burn firmware via only USB(DP/DM) to MCU(DP/DM) like the way of Betaflight?

As my understanding, the firmware from Betaflight is like to adjust the peripherals of MCU like turn on UART… Hope I’m not wrong.

Also, how should we understand boot loader mode?

Thanks

[TDK]

The system bootloader supports USB DFU, so yes you can flash over USB. Read AN2606 for additional insight.
You can enter the boot loader by holding BOOT0 high during reset, or by jumping to it within your code.

[Tesla DeLorean]

The NUCLEO board doesn't expose the DP/DM of the MCU to a USB connector.

But yes, chips supporting USB/DFU mode (as indicated by AN2606), will present as an "STM32 BOOT" type device if reset with BOOT0 HIGH, a working external clock (HSE), and connectivity of DP/DM to a USB cable/connector.

Most boards supporting this tend to have two buttons, BOOT and RESET, where you keep pressing BOOT and click RESET.

Or you have a BOOT button, that you press while connecting the USB/POWER source. Not otherwise powered from another source.