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slow boot from Bank2 STM32L4

Question asked by Micha K on Mar 29, 2017

Hi everyone,


I want to use the dualbank boot and upgrade mechanism as described in AN4767 with my STM32L476.

Toggling the booting bank with the BFB2 flag works fine.


Unfortunately, I observed that the booting process takes considerably longer when BFB2 flag is set.

I know that when the BFB2 flag is set the system memory bootloader evaluates the contents of the

Bank2 and changes the memory aliasing. But does this task really needs 20ms extra?
I developed a small binary which only sets a GPIO PIN to high in the main().
I measured the time between Power up and GPIO manipulation with an oszilloscope and the following setups:
binary-012,1ms (boots from bank1)
-binary132,2ms (boots from bank2)
binary-132,2ms (boots from bank1)


for all: Boot0 = 0 Boot1 =1 (independent of RDP level)

As you can see the booting process needs 20ms extra when BFB2 is set.


Is this amount of time reasonable?

Is there anything else I have to consider?


A short booting time is very important for my application.


Thank you very much for your help,


Best regards,