Use a fixed starting address for flash fds

[Gert]

Im am running a nrf528322 board with the s332 softdevice using sdk14.2.

I have implemented flash storage in my program according to the nordic flash_fds example.
This works fine.
We need to externally program some parameters in flash using nrfjprog. When I debug the flash code I see that sometimes the start address where the data is stored changes.

How can I best adjust my code to set a fixed flash start address? And how do I best determine where to start writing?

[Håkon Alseth]

Hi,

 

FDS is designed to use the upper part of the flash (and go downwards), and if there's a bootloader present (set in UICR), it will start below that address instead.

This is calculated in fds.c::flash_end_addr():

static uint32_t flash_end_addr(void)
{
    uint32_t const bootloader_addr = NRF_UICR->NRFFW[0];
    uint32_t const page_sz         = NRF_FICR->CODEPAGESIZE;
#ifndef NRF52810_XXAA
    uint32_t const code_sz         = NRF_FICR->CODESIZE;
#else
    // Number of flash pages, necessary to emulate the NRF52810 on NRF52832.
    uint32_t const code_sz         = 48;
#endif

    return (bootloader_addr != 0xFFFFFFFF) ? bootloader_addr : (code_sz * page_sz);
}

 

Note that if you're going to initialize fds manually, you'll need to match the amount of pages it uses as well. If the configuration states 3 flash pages, you need to add the proper tags on the upper 3 pages (2 x data, 1 x swap).

 

Best regards,

Håkon