USB Mass Storage sample not building with LittleFS on SDK 2.9 (nrf52840)

[Rodrigo G]

I'm trying to get the USB Mass Storage sample working on the nRF52840 using SDK 2.9. I followed the official guide here:
https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/samples/subsys/usb/mass/README.html

My goal is to use LittleFS as the storage backend for the USB Mass Storage device. However, when I try to build the sample using the following command:

west build -b nrf52840dk/nrf52840 samples/subsys/usb/mass -- -DCONFIG_APP_MSC_STORAGE_FLASH_LITTLEFS=y

I get a build error. I also tried with SDK 2.7 just in case, but I ran into the same issue.


I came across a similar question on the forums:
https://devzone.nordicsemi.com/f/nordic-q-a/117539/fs_sample-doesn-t-work-in-my-nrf52840-dk
But in that case, the suggested workaround was to use RAM instead of flash for storage, which doesn't quite fit my use case.

Am I missing something in the configuration? Is LittleFS currently supported as a backend for the USB MSC sample on nRF52840?

Thanks in advance

[Rodrigo G]

The specific error is:

 
C:/ncs/v2.9.0-nRF54H20-1-rc2/zephyr/drivers/disk/flashdisk.c:533:1: error: return type defaults to 'int' [-Werror=implicit-int]
533 | PM_FOREACH_AFFILIATED_TO_disk(DEFINE_FLASHDISKS_CACHE)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:/ncs/v2.9.0-nRF54H20-1-rc2/zephyr/drivers/disk/flashdisk.c: In function 'PM_FOREACH_AFFILIATED_TO_disk':
C:/ncs/v2.9.0-nRF54H20-1-rc2/zephyr/drivers/disk/flashdisk.c:572:30: error: storage class specified for parameter 'flash_disks'
572 | static struct flashdisk_data flash_disks[] = {
| ^~~~~~~~~~~
C:/ncs/v2.9.0-nRF54H20-1-rc2/zephyr/drivers/disk/flashdisk.c:572:15: error: parameter 'flash_disks' is initialized
572 | static struct flashdisk_data flash_disks[] = {
| ^~~~~~~~~~~~~~
C:/ncs/v2.9.0-nRF54H20-1-rc2/zephyr/drivers/disk/flashdisk.c:573:39: error: 'DEFINE_FLASHDISKS_DEVICE' undeclared (first use in this function)
573 | PM_FOREACH_AFFILIATED_TO_disk(DEFINE_FLASHDISKS_DEVICE)
| ^~~~~~~~~~~~~~~~~~~~~~~~

....

[Hieu]

Hello Rodrigo,

Could you please share your compiled partitions.yml file?

Hieu

[Rodrigo G]

Hello Hieu,
This is the content of  build/partitions.yml :

app:

  address: 0x0

  end_address: 0xfa000

  region: flash_primary

  size: 0xfa000

littlefs_storage:

  address: 0xfa000

  end_address: 0x100000

  placement:

    before:

    - end

  region: flash_primary

  size: 0x6000

sram_primary:

  address: 0x20000000

  end_address: 0x20040000

  region: sram_primary

  size: 0x40000

[Hieu]

Hello Rodrigo,

Could you please add the following under your littlefs_storage node?

littlefs_storage:
  affiliation:
  - disk

The background is explained here: https://docs.nordicsemi.com/bundle/ncs-2.9.1/page/nrf/scripts/partition_manager/partition_manager.html#configuration_file_format

[Rodrigo G]

Thank you for your response. However, I’m not sure where exactly I should add the littlefs_storage node.

I haven’t defined the littlefs_storage node in my configuration, and I could not find it in the available overlays in the sample I’m using.

Could you please clarify whether I need to create a new Device Tree overlay or modify an existing one? If you could point me to the specific file or location where this should be added, it would be very helpful.

[Hieu]

You will need to use a static Partition Manager configuration file. The simplest way to do so is copy partitions.yml to the root of your project and rename it pm_static.yml.

Then subsequent build will refer to that files for all the partitioning configurations.

In that file, you add the affiliation key and value under the littlefs_storage node.

For more information, please refer to https://docs.nordicsemi.com/bundle/ncs-2.9.1/page/nrf/scripts/partition_manager/partition_manager.html.

[Rodrigo G]

Hello,

I created the pm_static.yml file with the following contents, as you suggested:

littlefs_storage:

  affiliation:

  - disk

  address: 0xfa000

  end_address: 0x100000

  placement:

    before:

    - end

  region: flash_primary

  size: 0x6000

  cache-size: 0x1000

It seems that the file is correctly detected during the build.

-- Found partition manager static configuration : C:/ncs/v2.9.0-nRF54H20-1-rc2/zephyr/samples/subsys/usb/mass/pm_static.yml Partition 'littlefs_storage' is not included in the dynamic resolving since it is statically defined.

However, the build fails with the following error:

C:/ncs/v2.9.0-nRF54H20-1-rc2/zephyr/drivers/disk/flashdisk.c:519:54: error: 'PM_LITTLEFS_STORAGE_EXTRA_PARAM_disk_cache_siz' undeclared here (not in a function)
519 | #define PM_FLASH_DISK_ENTRY_EXTRA_PARAM(name, param) PM_##name##_EXTRA_PARAM_disk_##param
| ^~~
C:/ncs/v2.9.0-nRF54H20-1-rc2/zephyr/drivers/disk/flashdisk.c:529:24: note: in expansion of macro 'PM_FLASH_DISK_ENTRY_EXTRA_PARAM'
529 | PM_FLASH_DISK_ENTRY_EXTRA_PARAM(n, cache_size))
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:/ncs/v2.9.0-nRF54H20-1-rc2/zephyr/drivers/disk/flashdisk.c:531:69: note: in expansion of macro 'CACHE_SIZE'
531 | static uint8_t __aligned(4) PM_FLASH_DISK_CACHE_VARIABLE(n)[CACHE_SIZE(n)];
.....


This looks like a missing or undefined macro.

Shouldn’t this sample build out of the box without requiring extra configuration or changes like this?

If additional setup is indeed required for littlefs_storage, could you clarify the correct steps or provide a working example?

[Rodrigo G]

I finally get my sample to build by changing the pm_static.yaml as follows:

littlefs_storage:

  affiliation: disk

  extra_params: {

      disk_name: "littlefs",

      disk_cache_size: 4096,

      disk_sector_size: 512,

      disk_read_only: 0

    }

  address: 0xfa000

  end_address: 0x100000

  placement:

    before:

    - end

  region: flash_primary

  size: 0x6000