Flash durability of eDRX value storage on the nrf9160

[EFrank]

What is the durability, or number of expected lifetime cycles, of the persistent edrx value storage on the nrf9160. We're in a situation where we may update the value somewhat frequently, so we'd like to ensure we're not at risk of wear-leveling the device.

Additionally, does the modem have guards that avoid re-writing to the eDRX storage if the written value is the same as the stored value?

[Michal]

Hello,

Just changing the eDRX value won't immediately save it into the flash.

From the eDRX setting +CEDRXS AT command documentation:

The set command sets the requested eDRX parameters. The command configuration is stored to NVM approximately every 48 hours and when the modem is set to minimum functionality mode with the +CFUN=0 command.

What is the durability, or number of expected lifetime cycles, of the persistent edrx value storage on the nrf9160. We're in a situation where we may update the value somewhat frequently, so we'd like to ensure we're not at risk of wear-leveling the device.

We guarantee flash endurance of 10 000 writes.

Additionally, does the modem have guards that avoid re-writing to the eDRX storage if the written value is the same as the stored value?

I would assume that we do, but I would need to check that.

Best regards,

Michal

[EFrank]

Thanks for the reply, Michal.

Could you confirm whether or not those guards exist?

[Michal]

I am looking into it internally and I'll get back to you when I'll have an answer.

Best regards,

Michal

[Michal]

Hello, sorry for the delay. I hope to get an official answer to you soon.

Best regards,

Michal

[Michal]

The whole mechanism around it was much more complicated than I've expected, but in general:

- just updating the eDRX value doesn't cause any more flash wear than the periodic writes, the value gets saved to RAM

- consecutive writes are spread in memory, so that even periodic writes are not using the same flash area every time

- many settings are bunched together, so if there was any change, the next planned periodic write will happen

If you want to be on a very safe side, you can assume one write every 12h (but in reality it will be less often for a given flash area as said earlier).

Assuming not forcing writes to flash using AT+CFUN=0, which I assume you aren't doing?

Best regards,

Michal