Dual bank DFU with external flash

RE: Dual bank DFU with external flash

Einar Thorsrud — Wed, 29 Jan 2020 10:08:35 GMT

Hi,

[quote user="nono76352"]Would you recommand any size or type of external flash for storing the application ? Would a 128kB flash be enough (with no bootloader nor softdevice update planned) ?[/quote]

Assuming this should only hold an application update, the external flash does not need to be larger than the largest possible application (which is equal to the amount of free space between the SoftDevice and the bootloader).

[quote user="nono76352"]Is it possible to disable in the secure bootloader the ability to update the bootloader and the softdevice ?[/quote]

Yes. If you just want to do it in a simple way, you could modify postvalidate_sd_bl() in nrf_dfu_validation.c to always return false. But why would you want to do this? A SoftDevice update may not be possible anyway due to limitations in flash space, but what if for instance a vulnerability is found in the bootloader, and you are unable o update it?

RE: Dual bank DFU with external flash

Nathan O. — Wed, 29 Jan 2020 09:40:17 GMT

Thank you for your reply. I will have a look at the threads you provided.

Would you recommand any size or type of external flash for storing the application ? Would a 128kB flash be enough (with no bootloader nor softdevice update planned) ?

Is it possible to disable in the secure bootloader the ability to update the bootloader and the softdevice ?

RE: Dual bank DFU with external flash

Einar Thorsrud — Wed, 29 Jan 2020 09:31:39 GMT

Hi Nathan,

Using external flash for temporarily storing the new firmware is definitely possible, though we do not provide an example for it. There are a few existing threads about this, for instance, this and this.