Failsafe handle for unused program areas

[Morr]

Hello,

I would like to implement the following failsafe for unused program areas for nrf52.

1. Filled the unused program areas with undefined Instruction.

2. The UsageFault interrupt will be triggered if the PC points to an address in an unused area.

3. In the UsageFault interrupt route, implement the failsafe process such as soft reset.

I am using nrf52 with SoftDevice enabled and boot loader for dual bank DFU.

Is there any example / information to show how to do it?

Thank you.

[Vidar Berg]

Hello,

I think you may want to look into using the MPU and the BPROT — Block protection periperal for this purpose. But to answer your questions:

1. Unused parts of flash is typically just 1's, because that's the value the flash memory has after being erased.

2. It will lead to a fault exception.

3. Yes, you can re-define the hardfault execption handler in your application. 

e.g.

void HardFault_Handler(void)
{
    // Perform a reset to try recover the system
    NVIC_SystemReset(); 
}


int main(void)
{
    ...

We also have the HardFault handling library which can help you trace back to where the fault occured.

[Morr]

Hello,

Thank you for the example code and point to the HardFault handling library.

Regarding the MPU, there is not much information on the infocenter and also example code to show how to use it.

Could you share your idea how to use MPU for the failsafe handle?

Thank you.

[Vidar Berg]

We use the standard MPU made by ARM which you can read more about here: https://developer.arm.com/documentation/ddi0439/b/Memory-Protection-Unit/About-the-MPU?lang=en