About the DFU mode on a WeAct "BlackPill V2.0" - stm32F411. On the website : DFU Mode: Use the data line to connect to the computer. If there is an unrecognized problem, you can heat the chip appropriately (25°C) and then re-enter the ISP mode ....

[jlecl.1]

Could some one tell me explain why ?

[Peter BENSCH]

Welcome, @jlecl.1​, to the community!

One can only assume, because this is a hint from WeActStudio and not from ST.

Presumably they pointed it out on their Github site because it detunes the crystal oscillator a little and they hope that the slightly changed frequency will cause the DFU mode to synchronise.

Does it answer your question?

Regards

/Peter

[jlecl.1]

The crystal detunes was my first idea. 

As the advice to maintain at 25° the µC and not the crytal,I would like to knwo is there i some advice for DFU that I haven't read :)

[Peter BENSCH]

Well, that's in AN2606: STM32 microcontroller system memory boot mode, at the end of section 4.1:

For STM32 devices embedding bootloader using the DFU/CAN interface in which the external clock source (HSE) is required for DFU/CAN operations, the detection of the HSE value is done dynamically by the bootloader firmware and is based on the internal oscillator clock (HSI, MSI). When (because of temperature variations or other conditions) the internal oscillator precision is altered above the tolerance band (1% around the theoretical value), the bootloader might calculate a wrong HSE frequency value. In this case, the bootloader DFU/CAN interfaces might malfunction or not work at all.

I can only assume that WeActStudio hopes to get into the frequency band mentioned with the temperature change.

Regards

/Peter

[AScha.3]

maybe just a joke. (the chance to have a wrong setting pll is the reason for connection problem and some 25° clears this problem is about - try it at full moon. then it will work. )

if driver for usb/stm-dfu-device is on system, dfu device will be enumerated. otherwise - not.

heat up or freeze will change nothing.

[waclawek.jan]

As Peter said above, the issue is related to HSI precision and frequency change with temperature, because HSI used to determine the crystal's frequency.

JW

[jlecl.1]

perfect, it's clear for me.

Thanks all !