nRF52820 Flash write (fstorage, fds) at 2.7V

[Turnaev]

Hello!

I am having a problem using any internal flash writing libraries. If I set the REG0 voltage to 2.7V, the controller stops erasing the memory.

Moreover, I cant erase chip by swd too.

Why does the documentation not say a word about the fact that actually setting the voltage below 3V is one-time, after which the chip can no longer be rewritten without connecting to an external source with a voltage of 3V or higher?

[Amanda Hsieh]

Hi Turnaev, 

Are you using POFWARN which will prevent all flash writes? This is implemented in HW. From product specification, Power-fail comparator section:

If the power failure warning is enabled and the supply voltage is below the threshold, the power-fail comparator will prevent the NVMC from performing write operations to the flash.

-Amanda H.

[Turnaev]

Hello, Amanda!

Thank for your replay!

Unfortunately, the problem is somthing else.

I tried turning POFWARN on at 2.0, 2.5volts and fully disable. Nothing changes.

I have a Hardfault in a loop of waiting for a 32-bit word to be written to flash memory.

		if(NRF_NVMC->READY == 1)
		{
			NRF_NVMC->CONFIG = 1;
			__ISB();
			__DSB();
			
			for(uint8_t i = 0; i < 4; i++)
			{
				NRF_UICR->CUSTOMER[i] = tempCopyProtectID[i];
				while(NRF_NVMC->READY != 1);
			}
			
			NRF_NVMC->CONFIG = 0;
			__ISB();
			__DSB();
			
			while(NRF_NVMC->READY != 1);
		}

If I change Reg0 out to 3.0 or 3.3V all work good. But in my case I need voltage less.