Storing a few parameter bytes in flash

RE: Storing a few parameter bytes in flash

Kenneth — Tue, 09 Dec 2025 13:28:35 GMT

Hello,

You can't use the direct nvmc while actively advertising or in a connection no. So to workaround this there are two solutions:

1. Disconnect BLE for a short period of time to store the data.

2. Use timeslot to request a short period of time where you can use nvmc directly:
https://docs.nordicsemi.com/bundle/ncs-2.0.0/page/nrfxlib/mpsl/doc/timeslot.html

If you are interested in timeslot there is an old example here (this allow running a different radio protocol (ESB) in the timeslot, in your case you want to do the flash write instead), it may possible still be of use: https://github.com/too1/ncs-esb-ble-mpsl-demo

If you want to erase you need a 100ms window.

Kenneth

RE: Storing a few parameter bytes in flash

DiBosco — Tue, 09 Dec 2025 11:26:08 GMT

I have a question about this. Having seemingly got to just about being ready to give this to a customer for beta testing, it's more often than not crashing when I call:

nrfx_nvmc_page_erase
DuckDuckGoing about I have seen some 
suggestions that you cannot use nrfx_nvmc_page_erase when
you're using the soft device. 

Is that true? I can't really see how you could use any 
Nordic product without using soft device, so it seems unlikely
but maybe I'm missing something. Maybe I don't understand
properly what the soft device is. 

I'm using an nrf52840 with Zephyr as the OS, based on nrf Connect SDK2.0 and
using BLE with the 52840 acting as a central device. 

So, can I actually *not* use nrfx_nvmc_page_erase() 
in this scenario? 

If that is the case, I need to reask my question 
from half a year ago:

How do I store six bytes of data in internal flash please? The 
advice given by Kenneth seemed perfect, but now I have other 
aspects of the system going and I try to erae a sector it's all going wrong.

If Kenneth's method *is* suitable for my setup, any idea 
why it might by crashing innrfx_nvmc_page_erase() please?

RE: Storing a few parameter bytes in flash

DiBosco — Thu, 04 Sep 2025 12:37:49 GMT

Hi, thanks, finally came back to this project after giving up on it and this provides the answer I need. Wasted a lot of time on the first, incorrect one.

Many thanks for that.

RE: Storing a few parameter bytes in flash

Kenneth — Wed, 20 Aug 2025 13:09:33 GMT

Hello,

Presuming you reserve a flash page (either in an dts overlay or using partition manager (if partition manager is enabled the partitioning is done in pm_static.yml file (dts is ignored))).

Then in theory you should be able to do something like:

#define FLASH_ADDR 0x000F8000

uint32_t value;

// Read value
value = *((volatile uint32_t *)FLASH_ADDR);

// Erase page
(void) nrfx_nvmc_page_erase(FLASH_ADDR);

//Write value
nrfx_nvmc_word_write(FLASH_ADDR, value);

Kenneth

RE: Storing a few parameter bytes in flash

DiBosco — Fri, 15 Aug 2025 14:35:57 GMT

Hello, earth calling Nordic. Is there no-one there who can offer some assistance on this? I can see no difference between any of the config files in a plain write to flash demo (which works) and my modified central uart demo (which just returns -22 error. I've spent a week trying to get six bytes written to on-chip flash,this is madness.

RE: Storing a few parameter bytes in flash

DiBosco — Fri, 15 Aug 2025 09:07:22 GMT

A little more shouting into the void. Tried putting this in an overlay file

/delete-node/ &storage_partition;

&flash0 {
 partitions {
 /* Set 48KB of storage at the beginning of bank2 in order to have 3 sectors smaller than 32K
 * (nvs.h: uint16_t sector_size)
 */
 storage_partition: partition@f8000 {
 label = "storage";
 reg = <0x000f8000 0x00008000>;
 };
 };
};
No difference, still -22 error.

RE: Storing a few parameter bytes in flash

DiBosco — Thu, 14 Aug 2025 17:06:32 GMT

I feel like I'm shouting into the void. More investigation seems like maybe I need one of these overlay files? With something like this:

/delete-node/ &storage_partition;

&flash0 {
    partitions {
        /* Set 48KB of storage at the beginning of bank2 in order to have 3 sectors smaller than 32K
         *     (nvs.h: uint16_t sector_size)
         */
        storage_partition: partition@100000 {
            label = "storage";
            reg = <0x000100000 DT_SIZE_K(48)>;
        };
    };
};

Is that right? If so, which one? I finally worked out how to make a new project with a 52840 using nvs project and the dts file has this:

&flash0 {
 /*
 * For more information, see:
 * docs.zephyrproject.org/.../index.html
 */
 partitions {
 compatible = "fixed-partitions";
 #address-cells = <1>;
 #size-cells = <1>;

 boot_partition: partition@0 {
 label = "mcuboot";
 reg = <0x000000000 0xd000>;
 };
 slot0_partition: partition@d000 {
 label = "image-0";
 reg = <0x0000d000 0x30000>;
 };
 slot1_partition: partition@3d000 {
 label = "image-1";
 reg = <0x0003d000 0x1000>;
 };
 storage_partition: partition@3e000 {
 label = "storage";
 reg = <0x0003e000 0x00002000>;
 };
 };
};

So could I create a custom overlay file with this in? 
Would I need all the guff or just this:

 storage_partition: partition@3e000 {
 label = "storage";
 reg = <0x0003e000 0x00002000>;

?
I just can't get my head around how my original project doesn't complain 
I don't seem to havestorage_partition
defined anywhere. What's the score here?

Any chance of some guidance here please?

RE: Storing a few parameter bytes in flash

DiBosco — Thu, 14 Aug 2025 13:18:55 GMT

So, trawling through endless posts here, it seems maybe you can't just reference this nvs code and you need to add something to this .dts file thing. I've tried looking through some more example files and looks like maybe you need something like this:

&flash0 {

    partitions {
        compatible = "fixed-partitions";
        #address-cells = <1>;
        #size-cells = <1>;

        boot_partition: partition@0 {
            label = "mcuboot";
            reg = <0x00000000 0x0000C000>;
        };
        slot0_partition: partition@c000 {
            label = "image-0";
            reg = <0x0000C000 0x00076000>;
        };
        slot1_partition: partition@82000 {
            label = "image-1";
            reg = <0x00082000 0x00076000>;
        };

        /*
         * The flash starting at 0x000f8000 and ending at
         * 0x000fffff is reserved for use by the application.
         */

        /*
         * Storage partition will be used by FCB/LittleFS/NVS
         * if enabled.
         */
        storage_partition: partition@f8000 {
            label = "storage";
            reg = <0x000f8000 0x00008000>;
        };
    };
};

But if I put that in mine it stops compiling. Can I even just take another flash segment from a different project's dts file?

RE: Storing a few parameter bytes in flash

DiBosco — Wed, 13 Aug 2025 14:49:16 GMT

Just for completeness' sake, this is how I initialise the flash, I'm blindly following the example code which makes little sense to me and I can find no documentation which explains how this initialisation is supposed to work.

static struct nvs_fs fs;


#define NVS_PARTITION storage_partition
#define NVS_PARTITION_DEVICE FIXED_PARTITION_DEVICE(NVS_PARTITION)
#define NVS_PARTITION_OFFSET FIXED_PARTITION_OFFSET(NVS_PARTITION)

#define MAC_ADDR_ID 1

int flash_init(void)
{

 int ret_val;
 int rc = 0, cnt = 0, cnt_his = 0;
 struct flash_pages_info info;

 // Goodness knows what ret_val is all about, issues seem to return 0 in the example 
 // code, so let's return 1 if all is well. Suspect it was due to poor programming
 // with multiple returns in the example code though, and is likely unecessary
 ret_val = 1; 

 /* define the nvs file system by settings with:
 * sector_size equal to the pagesize,
 * 3 sectors
 * starting at NVS_PARTITION_OFFSET
 * Eh? What on earth is this on about?
 */
 fs.flash_device = NVS_PARTITION_DEVICE;
 if (!device_is_ready(fs.flash_device)) 
 {
 printk("Flash device %s is not ready\n", fs.flash_device->name);
 ret_val = 0;
 }
 else
 {
 fs.offset = NVS_PARTITION_OFFSET;
 rc = flash_get_page_info_by_offs(fs.flash_device, fs.offset, &info);
 if (0 != rc) 
 {
 printk("Unable to get page info, rc=%d\n", rc);
 ret_val = 0;
 }
 else
 {
 fs.sector_size = info.size;
 fs.sector_count = 3U;

 rc = nvs_mount(&fs);
 if (0 !=rc) 
 {
 printk("Flash Init failed, rc=%d\n", rc);
 ret_val = 0;
 }
 }

 }

 return ret_val;

}

RE: Storing a few parameter bytes in flash

DiBosco — Wed, 13 Aug 2025 13:55:03 GMT

Might need to rewrite it, certainly need to give the possibility.

That link seems to be totally irrelevant to what I'm trying to do. I've set up the example code to use

nvs_write() but it returns -22. 

enum sys_status flash_user_write(uint8_t *data_ptr, size_t len)
{
 
 ssize_t bytes_written;
 enum sys_status ret_val;

 bytes_written = nvs_write(&fs, MAC_ADDR_ID, data_ptr, len);
 if (len == bytes_written)
 ret_val = SYS_OK;
 else
 ret_val = SYS_FLASH_WR_ERR;

 return ret_val;

}
bytes_written is -22.
fs is valid, MAC_ADDR_ID is set to 1. I've tried following the code in 
nvs_write but my eyes glaze over at things like multiple returns
from a function (a BIG no-no),
comments that don't match with the code, about fifty squillion function
calls within function calls, returns like this 😮:

 return (addr >= boundary_start &&
 (addr < (boundary_start + boundary_size)) &&
 (len <= (boundary_start + boundary_size - addr)));

and impossible to understand variable names.
Again I'll say with the STM32 it's simple; you unlock flash to be
written and do this for a 16-bit value:

*(volatile u16 *)address = data_to_program;

Unlocking the flash is three lines of code.

You follow this nrf code though and it's mind boggling how convoluted it is. 

RE: Storing a few parameter bytes in flash

runsiv — Wed, 13 Aug 2025 12:11:10 GMT

True. Is this you want to write once or something you would like to update?

A coworker recommended having a look how it is done here, in the sample it's writing to UICR but it is same for to write to the flash.

Regards

Runar

RE: Storing a few parameter bytes in flash

DiBosco — Wed, 13 Aug 2025 11:26:39 GMT

Yes, but this is the filesystem example which is what I'm questioning. Is this really the only way to write and read six bytes to/from flash memory?

RE: Storing a few parameter bytes in flash

runsiv — Wed, 13 Aug 2025 11:18:34 GMT

Just so that I know, which version of NCS are you using? In general I would say maybe check out the following sample https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/samples/subsys/nvs/README.html#nvs

Here i think maybe you can use the setting partition as it is meant for storing persistent per device configuration and runtime states. Please see the documentation here, it also includes a example on how to use it

Regards

Runar