External NOR Flash use-case in nRF9161 FW upgrades

[ben_int]

We wanted to understand better the use of external NOR Flash for nRF9161 applications. For example, in nRF9161-DK, this would be the GD25WB256E chip.

1. For modem delta fw upgrades, does the workflow use external flash?
2. For application fw upgrades, does the workflow use external flash?
3. I read that external flash is useful for full modem firmware upgrades. What qualifies as a full modem firmware upgrade?
   
   • Is it moving from 1.0.0 to 1.3.6? (I pulled up some version numbers from nRF9160 for example here)
   • In the past, other vendors have provided special test modem FW to run in the field if we encounter a bug. Would similar scenarios warrant a full modem upgrade?

These answers would help us determine if we can exclude this flash from our custom board design. 

[Sigurd Hellesvik]

Hi,

To understand more about FOTA in the nRF Connect SDK, see DevAcademy Intermediate: Lesson 8 – Bootloaders and DFU/FOTA.

• For modem delta fw upgrades, does the workflow use external flash?
• For application fw upgrades, does the workflow use external flash?

In theory, you don't have to use external flash. In practice, you will pretty much always want external flash because you need space for your application code in internal flash. In the end, it depends on your application size.

What qualifies as a full modem firmware upgrade?

Erase all old modem firmware and overwrite it all with new modem firmware.

Is it moving from 1.0.0 to 1.3.6? (I pulled up some version numbers from nRF9160 for example here)

In this case, it is often possible to do a couple of delta modem updates instead, with the same effect but smaller memory footprint.

In the past, other vendors have provided special test modem FW to run in the field if we encounter a bug. Would similar scenarios warrant a full modem upgrade?

I will have to check this and get back to you.

Regards,
Sigurd Hellesvik

[ben_int]

Thanks for the response and the Bootloader/FOTA documentation link.

We are planning to leverage the SLM application for our product. Upon reviewing the latest .hex size for this application from Nordic website, without any code trimming, it is ~800kB.

There is only 200kB left, which isn't enough for a dual slot upgrade (which is needed for FOTA).

So we will move forward with including NOR flash. 

[Udi Vahaba]

Hi!
Have you succeeded in loading new firmware to the external flash and then using mcuboot to make the DFU?

I'm stuck on the point where my new firmware is on the external flash, but I can't make the application to upgrade.

[Sigurd Hellesvik]

Hi Udi,

Maybe this guide can help you?
https://academy.nordicsemi.com/courses/nrf-connect-sdk-intermediate/lessons/lesson-8-bootloaders-and-dfu-fota/