nrfjprog --program seems to be overwriting values I've written to flash with nrf_nvmc

[Maipei]

Hi all,

I'm working on an application with the nrf52840, and I'm having trouble making data persist over reprogramming (Using nrfjprog); after I reflash my board, the data that I've previously written is gone. My app-level code uses the nrf_nvmc functions to write to flash. So my question is this: do I need to use fstorage, or some other set of functions different than nrf_nvmc, to write to flash? Or is it based on how I configure my flash, rather than what functions I use to write to it? I've seen posts abut setting DFU_APP_DATA_RESERVED to create reserved space, but these were always in relation to DFU, rather than reflashing using nrfjrpog. Is there a difference between the two? Or should what works for one work for the other?

Thanks.

[Vidar Berg]

Hi, 

The user data should not be overwritten as long as it doesn't overlap with the new application FW assuming you are not doing a full chip erase during reprogramming. 

• nrfjprog --program *hex --sectorerase // erases necessary flash pages to fit the new program file.  

Is the user data stored in a separate section of flash ensuring that it is not overwritten when you upload the new app?  

[Maipei]

Hi Vidar,

Thanks for the reply. I am not sure if I am programming into a separate section or not. The drivers that I've written use the `nrf_nvmc_write_bytes` function to write, and I am writing to addresses between 0x00 and 0x40. To be honest, I'm not sure where that is in the memory map. I had assumed that address 0 would automatically be set to just above the application and softdevice locations in memory, but perhaps that is not the case.

After doing some more research, I think that the problem may be that I am using nrf_nvmc to write directly to the flash, but those operations are illegal while the softdevice is enabled, and I should be using fstorage instead, as it can be compatible with an enabled softdevice. I think that this may be my core problem, but I am still curious as to where in the memory map 0 lies when used as an address in a flash write. I am assuming that I will have to rework my drivers with fstorage rather than nrf_nvmc, and so I will still need to ensure that I am writing to the correct location.

[Vidar Berg]

Hi,

You can access the NVMC prior to enabling the softdevice, but not after. Reason for this is that the CPU is blocked during flash operations, which can interfere with BLE events. The softdevice provides flash API for safe scheduling of flash operations between events. 

Relevant documentation and modules for flash handling while Softdevice is enabled:

• SD flash memory API (sd_flash_page_erase, sd_flash_write)
• FDS
• fstorage
• Memory layout - User data is typically stored in a separate section at the end of flash or below bootloader code. 

[Maipei]

HI Vidar,

This answers my question. Thanks for your help.