How to select page size when using MCUboot with external flash memory?

[diocorreia]

Hi!

I'm using an external flash (SPI NOR) to store the secondary partition slot of MCUboot. According to datasheet, the SPI NOR chip in use supports 4KB, 32KB and 64KB paging. Despite this, if I set any other value than 4096 for CONFIG_SPI_NOR_FLASH_LAYOUT_PAGE_SIZE, MCUboot fails to load. Everywhere I look, I see people using or suggesting to use pages with 4096, but cannot understand the underlying reason. One guess I can take is that paging needs to match between the internal (nrf9151) and external flash, but I can't find any info to sustain this hypothesis.

[00:00:00.782,562] <inf> lwm2m_firmware: Image is confirmed OK                                                                              
[00:00:00.782,562] <inf> lwm2m_firmware: Firmware failed to be updated 

[Hakon]

Hello,

do you have a pm_static.yml file? Can you show what it looks like?

[diocorreia]

Be aware, my pm_static.yml is a copy from the auto-generated one.

EMPTY_0:
  address: 0xc000
  end_address: 0x10000
  placement:
    before:
    - mcuboot_pad
  region: flash_primary
  size: 0x4000
EMPTY_1:
  address: 0xfa000
  end_address: 0x100000
  placement:
    after:
    - settings_storage
  region: flash_primary
  size: 0x6000
app:
  address: 0x18000
  end_address: 0xf8000
  region: flash_primary
  size: 0xe0000
external_flash:
  address: 0xe8000
  end_address: 0x400000
  region: external_flash
  size: 0x318000
mcuboot:
  address: 0x0
  end_address: 0xc000
  placement:
    before:
    - mcuboot_primary
  region: flash_primary
  size: 0xc000
mcuboot_pad:
  address: 0x10000
  end_address: 0x10200
  placement:
    align:
      start: 0x8000
    before:
    - mcuboot_primary_app
  region: flash_primary
  size: 0x200
mcuboot_primary:
  address: 0x10000
  end_address: 0xf8000
  orig_span: &id001
  - app
  - mcuboot_pad
  - tfm
  region: flash_primary
  size: 0xe8000
  span: *id001
mcuboot_primary_app:
  address: 0x10200
  end_address: 0xf8000
  orig_span: &id002
  - app
  - tfm
  region: flash_primary
  size: 0xe7e00
  span: *id002
mcuboot_secondary:
  address: 0x0
  device: DT_CHOSEN(nordic_pm_ext_flash)
  end_address: 0xe8000
  placement:
    align:
      start: 0x4
  region: external_flash
  share_size:
  - mcuboot_primary
  size: 0xe8000
mcuboot_sram:
  address: 0x20000000
  end_address: 0x20008000
  orig_span: &id003
  - tfm_sram
  region: sram_primary
  size: 0x8000
  span: *id003
nonsecure_storage:
  address: 0xf8000
  end_address: 0xfa000
  orig_span: &id004
  - settings_storage
  region: flash_primary
  size: 0x2000
  span: *id004
nrf_modem_lib_ctrl:
  address: 0x20008000
  end_address: 0x200084e8
  inside:
  - sram_nonsecure
  placement:
    after:
    - tfm_sram
    - start
  region: sram_primary
  size: 0x4e8
nrf_modem_lib_rx:
  address: 0x2000a568
  end_address: 0x2000c568
  inside:
  - sram_nonsecure
  placement:
    after:
    - nrf_modem_lib_tx
  region: sram_primary
  size: 0x2000
nrf_modem_lib_sram:
  address: 0x20008000
  end_address: 0x2000c568
  orig_span: &id005
  - nrf_modem_lib_ctrl
  - nrf_modem_lib_tx
  - nrf_modem_lib_rx
  region: sram_primary
  size: 0x4568
  span: *id005
nrf_modem_lib_tx:
  address: 0x200084e8
  end_address: 0x2000a568
  inside:
  - sram_nonsecure
  placement:
    after:
    - nrf_modem_lib_ctrl
  region: sram_primary
  size: 0x2080
otp:
  address: 0xff8108
  end_address: 0xff83fc
  region: otp
  size: 0x2f4
settings_storage:
  address: 0xf8000
  end_address: 0xfa000
  inside:
  - nonsecure_storage
  placement:
    align:
      start: 0x8000
    before:
    - end
  region: flash_primary
  size: 0x2000
sram_nonsecure:
  address: 0x20008000
  end_address: 0x20040000
  orig_span: &id006
  - sram_primary
  - nrf_modem_lib_ctrl
  - nrf_modem_lib_tx
  - nrf_modem_lib_rx
  region: sram_primary
  size: 0x38000
  span: *id006
sram_primary:
  address: 0x2000c568
  end_address: 0x20040000
  region: sram_primary
  size: 0x33a98
sram_secure:
  address: 0x20000000
  end_address: 0x20008000
  orig_span: &id007
  - tfm_sram
  region: sram_primary
  size: 0x8000
  span: *id007
tfm:
  address: 0x10200
  end_address: 0x18000
  inside:
  - mcuboot_primary_app
  placement:
    before:
    - app
  region: flash_primary
  size: 0x7e00
tfm_nonsecure:
  address: 0x18000
  end_address: 0xf8000
  orig_span: &id008
  - app
  region: flash_primary
  size: 0xe0000
  span: *id008
tfm_secure:
  address: 0x10000
  end_address: 0x18000
  orig_span: &id009
  - mcuboot_pad
  - tfm
  region: flash_primary
  size: 0x8000
  span: *id009
tfm_sram:
  address: 0x20000000
  end_address: 0x20008000
  inside:
  - sram_secure
  placement:
    after:
    - start
  region: sram_primary
  size: 0x8000

[diocorreia]

I think I finally found out the reason behind it. But maybe some confirmation from your side would also be good :D

I think it has to do with the boot swap method I'm using (BOOT_PREFER_SWAP_MOVE) which requires "all sectors in both slots being of the same size". And since pages on internal flash have 4096KiB, that's why I only can use such value on the external flash with secondary slot.

[Hakon]

That seems like a very plausible reason indeed.