For a freshly soldered STM32F4 chip on a consumer product, is the chip defaulted to allow USB DFU when usb cable is plugged in .

[Baze]

I can't imagine for pre-production to have to tie boot to vcc or the like as it is described on the discovery boards. Would be complicated to do this and will have to introduce additonal circuitry like a switch or rc circuit. If so can someone provide the stm reference to it, that would be much appreciated.

[Ozone]

You might need to tell the exact name of the MCU variant you talk about.

At least none of the lower-digits F4 variants I know supports USB within the system bootloader.

USB is a bit picky with clock tolerance, the default internal RC oscillator does not meet the specs.

[Baze]

STM32F401VBT6TR, how do companies get by then?

[Tesla DeLorean]

For F2 or F4 you need BOOT0 High for System Boot Loader for Serial or USB connectivity.

So a jumper or test fixture.

Most use JTAG I'd presume.

Newer L0 and L4 parts enter the ROM when the FLASH is blank, but this has its own issues with requiring a power cycle.​

[Ozone]

> Most use JTAG I'd presume.

I would second that.

Most projects involving programming MCUs during production/test process I did used JTAG.

Pods are relatively cheap, provide high data rates, and support cmd line or embeddable access.

Most often, just the pads for test needle access are provided with the PCB layout.

An additional benefit is the ability to quickly add a debug connector for prototypes.

[Baze]

@Community member​  @Ozone​ 

Thanks for replying, this isn't a standard high top board that may have header pins. It's a pretty thin board with a thin case, so I don't think Jumper is an option. If I include open pads, then the texting fixture takes care of jumping the board, and potentially uploading the firmware? No need for usb dfu then?

[Tesla DeLorean]

Generally the use of USB/UART with the System Boot Loader is facilitated by interfaces you already bring out.

People often use jumpers or buttons. If you use standard interfaces on the test stations, they can be scaled more cheaply.

JTAG/SWD is frequently used in test stations, and that can be facilitated by test points, edge castellations, break-off tabs, or whatever

[Pavel A.]

On small/thin boards, my customers use 6-pin Segger connectors. But the cable is quite expensive.

https://www.segger.com/products/debug-probes/j-link/accessories/adapters/6-pin-needle-adapter/