Maximum settings partition size estimation

RE: Maximum settings partition size estimation

Vidar Berg — Mon, 17 Jun 2024 09:04:21 GMT

Hi,

As mentioned in the NVS documentation, NVS will always keep one page empty to allow copying of existing data. Therefore, it is not possible to allocate less than 2 flash pages to NVS.

This extra flash page enables safe updating of existing data.

RE: Maximum settings partition size estimation

mlac — Sat, 15 Jun 2024 21:24:57 GMT

Hi Vidar,

I've included the following in my main():

	void *storage;
    int rc = settings_storage_get(&storage);
    ssize_t size = nvs_calc_free_space((struct nvs_fs *)storage);
    printk("Free space: %d\n", size);

According to the printed result, the free space doesn't exceed 4K, even though I've allocated 8K for storage.

my-board.dtsi:

&flash0 {
    partitions {
        compatible = "fixed-partitions";
        #address-cells = <1>;
        #size-cells = <1>;

        boot_partition: partition@0 {
            label = "mcuboot";
            reg = <0x0 0x10000>;
        };
        slot0_partition: partition@10000 {
            label = "image-0";
            reg = <0x10000 0xdd000>;
        };
        hardware_config_partition: partition@ed000 {
            label = "hardware-config";
            reg = <0xed000 0x1000>;
        };
        user_config_partition: partition@ee000 {
            label = "user-config";
            reg = <0xee000 0x10000>;
        };
        storage_partition: partition@fe000 {
            label = "storage";
            reg = <0xfe000 0x2000>;
        };
    };
};

pm_static.yml:

app:
  address: 0x10200
  end_address: 0xfe000
  region: flash_primary
  size: 0xede00
mcuboot:
  address: 0x0
  end_address: 0x10000
  placement:
    before:
    - mcuboot_primary
  region: flash_primary
  size: 0x10000
mcuboot_pad:
  address: 0x10000
  end_address: 0x10200
  placement:
    align:
      start: 0x1000
    before:
    - mcuboot_primary_app
  region: flash_primary
  size: 0x200
mcuboot_primary:
  address: 0x10000
  end_address: 0xfe000
  orig_span: &id001
  - app
  - mcuboot_pad
  region: flash_primary
  size: 0xee000
  span: *id001
mcuboot_primary_app:
  address: 0x10200
  end_address: 0xfe000
  orig_span: &id002
  - app
  region: flash_primary
  size: 0xede00
  span: *id002
hardware_config_partition:
  address: 0xed000
  end_address: 0xee000
  size: 0x1000
user_config_partition:
  address: 0xee000
  end_address: 0xfe000
  size: 0x10000
settings_storage:
  address: 0xfe000
  end_address: 0x100000
  placement:
    align:
      start: 0x1000
    before:
    - end
  region: flash_primary
  size: 0x2000
sram_primary:
  address: 0x20000000
  end_address: 0x20040000
  region: sram_primary
  size: 0x40000

Thanks in advance for your help!

RE: Maximum settings partition size estimation

Vidar Berg — Fri, 10 May 2024 12:53:16 GMT

Hello,

How much flash is used by settings is very application depended (number of setting entries and how frequent they are updated). I recommend using the nvs_calc_free_space() to help profile the flash usage for your application. Flash wear should also be considered: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/services/storage/nvs/nvs.html#flash-wear

You can use this function to retreive the NVS instance used by the settings module: https://github.com/nrfconnect/sdk-zephyr/commit/ccf8c547d090ad3f76dbfa64744f32333658dcdb

Best regards,

Vidar