Using flash pages manually

[OskarM]

Hi,

I would like to have one page of flash mapped manually to store information critical for the device. Let's assume I do not trust data preserving by DFU or there is a situation of PSTORAGE corruption after some messed up DFU.

Is there a way to "extract" one page of flash of known address so that is never used by a) programmer (somewhere in .ld file) b) bootloader & DFU? Thanks

[Einar Thorsrud]

You can reserve flash pages in the memory area between the application and the bootloader, right before the beginning of the bootloader. You can access this flash memory, but remember that it is still a protected resource by the SoftDevice, so you must use sd_flash_*() calls to access it. The Memory layout section of the bootloader documentation, and particularily Preserving application data explains the details.

[OskarM]

Is this area not connected with pstorage? I mean if I reserve here 2 pages and use pstorage of X blocks, then this adds up?

[Einar Thorsrud]

The area is also used by pstorage, but you can allocate as much as you need. You should consider both the number of pages needed by pstorage and needed by your application directly, and reserve the sum. Remember that you need to reserve at least two pages for pstorage (one swap page). That means that you need to reserve at least three pages, possibly more, depending on your application.

[OskarM]

I hoped for a really constant (hard coded) flash address. This solution puts on a programmer task of keeping pstorage pages under control and awareness of bootloader size (so the whole area doesn't move). But will have to live with that I assume. Thanks