Help with BLE DFU FOTA on External Flash (nRF52840, NCS 2.5.2)

Question

I am trying to get DFU FOTA over BLE to work using external flash on an nRF52840 DK with NCS 2.5.2 . I followed multiple sources, but I am unsure about the correct configuration. 1. Configuration Steps I started by adding these to prj.conf CONFIG_BOOTLOADER_MCUBOOT=y CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU=y This already causes compilation errors , but I will get back to that later. You can get the same errors by modifying the fs_sample and adding: CONFIG_BT=y CONFIG_BT_PERIPHERAL=y CONFIG_BOOTLOADER_MCUBOOT=y CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU=y 2. Partition configuration I have seen projects using pm_static.yml and others defining partitions in overlay , but I am not sure what the difference is. Here is my pm_static.yml external_flash: address: 0xf4000 end_address: 0x800000 region: external_flash size: 0x70c000 mcuboot_secondary: address: 0x00000 device: MX25R64 end_address: 0xf4000 region: external_flash size: 0xf4000 At the same time, my overlay file contains: &mx25r64 { partitions { compatible = "fixed-partitions"; #address-cells = <1>; #size-cells = <1>; /* 8MB external storage partition */ external_partition: partition@0 { reg = <0x00000000 0x0800000>; }; }; }; / { msc_disk0 { status = "okay"; compatible = "zephyr,flash-disk"; partition = <&external_partition>; disk-name = "NAND"; /* cache-size == page erase size */ cache-size = <4096>; }; }; Then I add this at the end of the overlay file: / { chosen { nordic,pm-ext-flash = &mx25r64; }; }; Does this conflict with pm_static.yml? 3. MCUBoot configuration Inside child_image/mcuboot.conf I added CONFIG_FLASH=y CONFIG_NORDIC_QSPI_NOR=y CONFIG_BOOT_MAX_IMG_SECTORS=256 CONFIG_LOG=y CONFIG_LOG_MODE_MINIMAL=y CONFIG_MCUBOOT_LOG_LEVEL_WRN=y CONFIG_CBPRINTF_NANO=y CONFIG_NORDIC_QSPI_NOR_FLASH_LAYOUT_PAGE_SIZE=4096 4. Compilation errors When compiling, I get these errors: /opt/nordic/ncs/v2.5.2/zephyr/drivers/disk/flashdisk.c:484:1: error: return type defaults to 'int' [-Werror=implicit-int] 484 | PM_FOREACH_AFFILIATED_TO_disk(DEFINE_FLASHDISKS_CACHE) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /opt/nordic/ncs/v2.5.2/zephyr/drivers/disk/flashdisk.c:524:39: error: 'DEFINE_FLASHDISKS_DEVICE' undeclared (first use in this function) 524 | PM_FOREACH_AFFILIATED_TO_disk(DEFINE_FLASHDISKS_DEVICE) | ^~~~~~~~~~~~~~~~~~~~~~~~ 5. Questions 1. Should I use pm_static.yml or overlay or both? - Are my external flash partitions conflicting between these two files 2. Why does MCUBoot fail to compile with these errors? - Is there a missing configuration option for flash-disk or QSPI