Mesh SDK - NRF52840 flash page issue

[Justin]

I am setting up a programming script for our devices.  
Memory layout is as follows:

	Address	Size
MBR+SoftDevice	0x00000	0x26000
Application	0x26000	0x66000
DFU Swap Space	0x8C000	0x66000
Persistent App Data	0xF2000	0x2000
Nordic Mesh Info	0xF4000	0x4000
Nordic Bootloader	0xF8000	0x6000
Bootloader Settings	0xFE000	0x2000

Programming the following items: SD, bootloader, our application, and device page produced by device_page_generator... The device functions as desired.
The issue is when I attempt to add the persistent app data pages, starting at 0xF2000.
It seems that something is using that page (and F3000):

J-Link>mem8 F2000 1024

000F2000 = 08 04 10 10 01 00 FF FF FF FF FF FF FF FF FF FF
...
000F2FF0 = FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
000F3000 = 08 04 10 10 01 00 FF FF FF FF FF FF FF FF FF FF

I thought I had properly accounted for the flash pages required by mesh.  
Calling the following functions shows that the DSM starts where I expect:
dsm_flash_area_get() = 0xF4000
net_state_flash_area_get() =  0xF5000
flash_manager_recovery_page_get() = 0xF6000

What have I missed?  What is using the flash pages at 0xF2000 and 0xF3000

Thanks.

Mesh SDK v3.1.0
nRF5 SDK v15.2.0

[Mttrinh]

Hi,

Which Mesh SDK version are you using?

[Mttrinh]

You seem to have missed mesh_config. You can use mesh_stack_persistence_flash_usage() to get out the actual memory usage of the mesh.

[Justin]

In mesh_sdk/doc/how_to_nordicSDK.md there is the following information:
 

Furthermore, when writing to flash, ensure to not write or erase areas utilized by the mesh stack
modules and the bootloader (if present). By default, the mesh modules utilize the last `x` number of
pages before the start of the bootloader, if present, or the last `x` number of pages of the
available flash on the Nordic SoC.
The value of `x` depends on the configuration of the mesh stack and can be calculated by:

    x = 2 + ACCESS_FLASH_PAGE_COUNT + DSM_FLASH_PAGE_COUNT

Based on my mesh sdk configuration, x = 4, which is why I have allocated 4 pages in my layout.

In mesh_sdk/doc/libraries/flash_manager.md there is the following information:

By default, the defrag recovery page is the last page before the bootloader starts, or the last page in device flash if the bootloader is not present (determined by the `UICR->BOOTLOADERADDR` register). This location can be overriden by defining `FLASH_MANAGER_RECOVERY_PAGE` in the compiler defines. Note that the recovery page should be the same page in every iteration of the firmware, to avoid loss of backed up recovery data.

So, this recovery page is not part of the 4 pages mentioned earlier in how_to_nordicSDK.md?
Also, I expect the recovery page to be at 0xF7000 not 0xF6000, since the bootloader begins at 0xF8000.  If the recovery page is actually at 0xF6000, what is using 0xF7000?

I have added the call to mesh_stack_persistence_flash_usage, and it returns the following values: start(0xF2000), size(0x5000).

So 5 pages are being used by SDK components.  What in the configuration accounts for the extra page?
I expected it to use 4 pages based on the information in how_to_nordicSDK.md.  

Thanks.

[Justin]

can you offer any additional comments on this? thanks!

[Mttrinh]

Hi,

Sorry for the late response.

It seems like you found some outdated documentation, I have reported this internally. It is the MBR that are using 0xF7000. You can have a look at the SDS for more information. The extra page you are seeing are for mesh_config.

[Justin]

I thought the MBR and bootloader settings were the last two pages in flash, FE000-FF000?  Has this changed?

Note that this is for the NRF52840 device.

[Mttrinh]

You can place the MBR wherever you want, but the mesh bootloader put it right before the bootloader starts.

[Justin]

Thanks, i was referencing a previous forum post, which is why i thought MBR was after the bootloader:
"Yes the bootloader uses the space at the end for MBR and bootloader setting."

Looking at the bootloader code, I see that it sets MBR in the UICR to the page before.
The bootloader is using 2 pages at the end for info and bank info.

You previously mentioned i was looking at outdated information.  Was that for the flash_manager.md?  
Is the following equation outdated:

x = 2 + ACCESS_FLASH_PAGE_COUNT + DSM_FLASH_PAGE_COUNT

Where can i find the current documentation for configuring mesh flash usage?
I understand that the mesh components are using 5 pages, starting at 0xF2000, but I would like to understand how my configuration is driving that.

Thanks!