stm32f4 using NVIC_SystemReset() fails to reset

[ari_v2]

Hello,

My board consists of stm32f427 and I have a strange problem.

Calling NVIC_SystemReset() causes CPU to hang. This happens only on some boards.

I could overcome the problem in one of the following:

• Add a HAL_Delay(100) before calling NVIC_SystemReset()
• Change code in NVIC_SystemReset() as follows:

   SCB->AIRCR = ((0x5FA << SCB_AIRCR_VECTKEY_Pos) |

               (SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) |

             SCB_AIRCR_SYSRESETREQ_Msk |               

SCB_AIRCR_VECTCLRACTIVE_Msk | SCB_AIRCR_VECTRESET_Msk)

   These 2 additional bits cause CPU to reset, although they are meant to be used only for debug

• Of course system will reset if I use the IWDG.

I read in forums that others encountered this problem but in my case it looks different:

• NRST pin has a pulldown 0.1uF.  NRST is not pulled up. As shown below in figure
• BOOT0 is connected to ground. 

Could anyone please explain:

Why NVIC_SystemReset() does not work on some boards?

How could the delay of 100 msec or setting system control register bypass the problem?

Thank you,

Ari

[TDK]

Only thing I can guess is if there's some flash operation still ongoing that is affecting things.

[Tesla DeLorean]

All very odd, don't have an explanation here.

Did you stop something else just prior to doing the reset? Flash Write or Erase? Turn off a PWM?

Is the capacitor really 100nF (0.1uF) and not something much larger?