NCS MCUboot and NVS

[Bryan]

NCS: 2.3.0

OS: Windows 10I have a question regarding how NVS is managed with MCUboot enabled.

So the way I understand it, when MCUboot is enabled, it automatically enabled partition manager.  This means all the flash partitions in the device tree are ignored.

Flash section from the custom project dts file...

&flash0 {

    partitions {

        compatible = "fixed-partitions";

        #address-cells = <1>;

        #size-cells = <1>;

        boot_partition: partition@0 {

            label = "mcuboot";

            reg = <0x000000000 0xC000>;

        };

        slot0_partition: partition@c000 {

            label = "image-0";

            reg = <0x0000C000 0x32000>;

        };

        slot1_partition: partition@3e000 {

            label = "image-1";

            reg = <0x0003E000 0x32000>;

        };

        scratch_partition: partition@70000 {

            label = "image-scratch";

            reg = <0x00070000 0xA000>;

        };

        storage_partition: partition@7e000 {

            label = "storage";

            reg = <0x0007e000 0x00002000>;

        };

    };

};

And the corresponding partition report with MCUboot enabled.  Clearly shows the dts &flash0 is ignored.

PS C:\Virtuix\nordic\myapps\o1_agg_nrf52833\build> west build -t partition_manager_report
-- west build: running target partition_manager_report
[1/1] cmd.exe /C "cd /D C:\Virtuix\nordic\myapps\o1_agg_n...rtuix/nordic/myapps/o1_agg_nrf52833/build/partitions.yml" flash_primary (0x80000 - 512kB):
+-------------------------------------------------+
| 0x0: mcuboot (0x6000 - 24kB) |
+---0x6000: mcuboot_primary (0x3c000 - 240kB)-----+
| 0x6000: mcuboot_pad (0x200 - 512B) |
+---0x6200: mcuboot_primary_app (0x3be00 - 239kB)-+
| 0x6200: app (0x3be00 - 239kB) |
+-------------------------------------------------+
| 0x42000: mcuboot_secondary (0x3c000 - 240kB) |
| 0x7e000: EMPTY_0 (0x1000 - 4kB) |
| 0x7f000: nvs_storage (0x1000 - 4kB) |
+-------------------------------------------------+

This does not seem to be the case for NVS storage.  I want to limit the size of NVS to as small as possible so as much flash can be used MCUboot as possible.  I was told in another devzone post that the smallest number of flash pages that can be used is two (each page is 4096 bytes).  One for data and one for swap.

devzone.nordicsemi.com/.../partition-manager-and-nvs-size-change

What I discovered is there are configuration options in three different locations. 


1. prj.conf

CONFIG_FLASH=y

CONFIG_FLASH_PAGE_LAYOUT=y

CONFIG_NVS=y

# Each page is 4096 (0x1000) you need to set aside a minimum

# two flash pages (one for data and use for swap/scratch

CONFIG_PM_PARTITION_SIZE_NVS_STORAGE=0x2000   <<<<<<<<  Two  pages

2. dts file

        storage_partition: partition@7e000 {

            label = "storage";

            reg = <0x0007e000 0x00002000>;   <<<<<<< Matching 0x2000 (two pages)

        };

3. NVS init routine

int nvs_flash_init(void)

{

    int err;

    printk_inf("Initializing flash device...");

    /* define the nvs file system by settings with:

     *  sector_size equal to the pagesize,

     *  3 sectors

     *  starting at FLASH_AREA_OFFSET(storage)

     */

    //nvs_fs.flash_device = FLASH_AREA_DEVICE(STORAGE_NODE_LABEL); //NVS_PARTITION_DEVICE;   // updated for NCS 2.2.0

    nvs_fs.flash_device = NVS_PARTITION_DEVICE;  // updated for NCS 2.2.0

    if (!device_is_ready(nvs_fs.flash_device)) {

        printk_err("Flash device %s is not ready", nvs_fs.flash_device->name);

        return (-1);

    }

    //nvs_fs.offset = FLASH_AREA_OFFSET(STORAGE_NODE_LABEL); //NVS_PARTITION_OFFSET;        // updated for NCS 2.2.0

    nvs_fs.offset = NVS_PARTITION_OFFSET;       // updated for NCS 2.2.0

    ERR_CHECK(flash_get_page_info_by_offs(nvs_fs.flash_device, nvs_fs.offset, &nvs_info), "Unable to get flash page info");

    nvs_fs.sector_size = nvs_info.size;

    nvs_fs.sector_count = 2U;                <<<< Matching two pages/sectors

    ERR_CHECK(nvs_mount(&nvs_fs), "Unable to mount flash");

    printk_inf("Flash device intialized");

    return(0);

}

If any of them do not match, I get these error messages.

[00:00:01:002] <info> nvs: Initializing flash device...
[00:00:01.002,380] <err> flash_nrf: flash_nrf_read: invalid address: 0x00080ff8:8
[00:00:01.005,859] <err> flash_nrf: flash_nrf_read: invalid address: 0x00080000:32
[00:00:01:005] <error> nvs: Error -22 occurred in nvs_mount(&nvs_fs) in ../src/nvs.c line 60. Unable to mount flash

Can someone give a thorough explanation of "how" NVS is managed when MCUboot is enabled and how it should be properly configured?  Even though the above works as long as all three locations have matching configuration, it simply doesn't seem like the correct way to do it.

[Hieu]

Hi Bryan,

Can someone give a thorough explanation of "how" NVS is managed when MCUboot is enabled and how it should be properly configured?

To my understanding, NVS works the same way it always does. It is the partition that NVS will be initialized on that would be changed, which I understand is what you are asking by "how it should be properly configured."

From this point on, I will explain with information from NCS v2.3.0. The same details for older version of NCS should be the same or inferable from that.

The way the partitions are created is detailed in the Partition Manager documentation: 
Link: Partition Manager — nRF Connect SDK 2.3.0 documentation (nordicsemi.com)

When the Partition Manager is active, it overrides the partitions defined in DTS automatically. This is done by replacing Zephyr macros' implementations based on DTS with that based on Partition Manager.
Refer: https://github.com/nrfconnect/sdk-zephyr/blob/v3.2.99-ncs2/include/zephyr/storage/flash_map.h#L260-L262.

By default, when created automatically, a partition named nvs_storage is always created.
Refer: https://github.com/nrfconnect/sdk-nrf/blob/v2.3.0/subsys/partition_manager/pm.yml.nvs.

In the macro implementation replacement mentioned above, the default name of the storage partition in Zephyr is also replaced with "nvs_storage." 
Refer: https://github.com/nrfconnect/sdk-nrf/blob/v2.3.0/include/flash_map_pm.h#L36-L39

The size of this partition is configurable with CONFIG_PM_PARTITION_SIZE_NVS_STORAGE, the default size is 0x6000.
Refer:
Default size: https://github.com/nrfconnect/sdk-nrf/blob/v2.3.0/subsys/partition_manager/Kconfig#L71-L76.
Kconfig definition: https://github.com/nrfconnect/sdk-nrf/blob/v2.3.0/subsys/partition_manager/Kconfig.template.partition_config

---

It is a little weird that you said you need to keep #2. DTS file in sync with #1. Project Config and #3. Code. Are you certain that if you desync DTS with the rest, the setup will break?

This does not seem to be the case for NVS storage.  I want to limit the size of NVS to as small as possible so as much flash can be used MCUboot as possible.  I was told in another devzone post that the smallest number of flash pages that can be used is two (each page is 4096 bytes).  One for data and one for swap.

devzone.nordicsemi.com/.../quote]

This is right, please keep that in mind when tuning with CONFIG_PM_PARTITION_SIZE_NVS_STORAGE.

Hieu

[Bryan]

Hieu,

I retested and confirmed that I do NOT have to keep the dts file in sync.  That makes much more sense.  My mistake.  

Thank you for the detailed information.  That will be a very useful post to others.