Hi everyone! I want to know when the MCU STM32L4A is in system bootloader (by using a LED). Is this possible? Many thanks!

[Peter BENSCH · Accepted solution]

Welcome, @PGall.4​, to the community!

If you are talking about the internal bootloader in each STM32, its activity cannot be indicated with an LED.

However, if you write your own bootloader, you have all the freedom, but also the disadvantage of losing user flash.

Does it answer your question?

Regards

/Peter

[Tesla DeLorean]

Have a GPIO / LED that lights after reset​, have your code clear it.

[PGall.4]

Hi Peter!

Yes, I was talking about internal bootloader. We wanted to ensure that the MCU wasn't in that state with a visual indication,

Many thanks!

[Peter BENSCH]

Good idea, but requires a little extra hardware, e.g. an external flipflop.

[waclawek.jan]

I know this is a 2 month old thread resurrected probably by this badly handled spamming wave, but maybe this is a topic worth another answer.

The default bootloader sets pullups/pulldowns on some pins. AN2606 probably does not deal with this adequately and ST for whatever weird reason refuses to publish the bootloader sources, but you can disassemble/single-step the bootloader to see which ones - e.g. UART Rx pins. The pullups/pulldowns are nominally 40kOhm, and these days there are LEDs out there which light up quite adequately with currents like that.

Whether it's worth to spend a pin on this function is a question for OP to decide.

JW

[Peter BENSCH]

Very good idea that is worth pursuing.