NVIC_SystemReset() hangs

[Lu�s Magalh�es]

Hi there,

I've been working with a BT module and trying to use one of its pins to set the boot mode of the STM32F746IGT. I've set the pin HIGH and then issue the NVIC_SystemReset(), but nothing happens after that. I have a blue LED that is suppost to light up at the start of the program, and the LED just doesn't light up. Power cycling the module starts it again.

What could be causing the NVIC_SystemReset() to be hanging ?

Best regards,

Luís

[Tesla DeLorean]

The external NRST pin cannot be driven high via a push-pull driver

[Lu�s Magalh�es]

So the NRST pin should be left floating ? Won't that lead to some reset events occasionally ?

[Tomas DRESLER]

No, because there is weak pull-up inside STM32. You are allowed only open-drain configuration on pins driving NRST signal, because NVIC_SystemReset and all other internal reset sources rely on NRST going low.

[Lu�s Magalh�es]

Thank you, removing the pull-up resistor made the NVIC_SystemReset() routine to work. One question though: if BOOT0 is low and you set the definitions that if BOOT0 is low, it will go to bootloader mode, issuing a NVIC_SystemReset() will allow you to enter bootloader mode or will it just run the application again ?

[Tesla DeLorean]

I didn't say it needed to float, I said it must not be DRIVEN high, by some external circuitry. ​

[Lu�s Magalh�es]

Thank you all for the great help. And in case anyone is wondering, you can set the BOOT0 pin to the desired level and if you use NVIC_SystemReset() you will enter the bootloader mode. Great for firmware OTA upgrades.