MeshCore/docs/ota_nrf52_bootloader_update.md

nRF52 bootloader updates over LoRa

Selected nRF52840 repeater LoRa-OTA builds can replace their matching OTAFIX bootloader without replacing the running application. This is a privileged maintenance path, not a normal firmware update. It cannot bootstrap a stock or older bootloader: install the exact ABI-3 self-update-capable OTAFIX build once over USB/BLE DFU or SWD.

Storage layouts

Layout	Application limit	Staged boot package	Work area	Handoff / capability
XIAO-module raw QSPI	below 0xE0000	external QSPI offset 0	dedicated internal 0xE0000..0xEA000 scratch	source 0x51, flags 0x0E
Qualified internal-flash target	normal 0xED000 limit	shared internal slot, exact start 0xE2000	the same eleven-page slot; no second reservation	source 0xED, flags 0x0A

The internal path does not change the application linker or permanently set aside separate app-OTA, boot-package, and scratch regions. The ordinary bottom-aligned internal store holds one container at a time: either an application delta or a bootloader package.

The exact bootloader container is 41,330 bytes: 365 bytes of signed mOTA metadata, a 40 KiB payload, and the five-byte trailer. Below the normal 0xED000 store ceiling it bottom-aligns at 0xE2000. Admission requires a hash-valid live EndF proving the current application, including its trailer, ends at or before 0xE2000. OTAFIX then reads each source window before erasing and compacts the payload forward in place to the page-aligned raw range 0xE2000..0xEC000; it verifies every page and the whole image before asking the MBR to copy that image over 0xF4000..0xFE000.

An ordinary application delta can be smaller or larger than this eleven-page shape. It bottom-aligns dynamically below 0xED000 and may begin below 0xE2000; its detools workspace must stop at its actual container start, while the reconstructed application must stop below 0xED000. The two package kinds are mutually exclusive because they use the same store.

For internal-self-update builds, an absent or corrupt live EndF disables all internal staging before the first erase. The older 608 KiB rescue estimate is unsafe when a normally linked application may extend to 0xED000. Builds without this feature retain the legacy rescue behavior.

Internal-flash target inventory

The release builder consumes the allowlist in tools/mota/nrf52_internal_bootloader_targets.txt. Ten names are also literal PlatformIO environments and are enabled automatically when built directly. The other eleven are release aliases assembled from a base environment plus the lean OTA overlay; build them through build.sh, which passes the same allowlist decision to the common pre-build guard. These lean repeater/bridge targets have no OTA-owned SD/QSPI store and have an exact curated OTAFIX manifest identity:

Build target(s)	Installed OTAFIX identity	Boot target ID
Heltec_tower_v2_repeater_lora_ota_no_external_sensors	239A0071 / TOWER_V2_OTA	1150F50E
T096 lean repeater and RS232 bridge	239A0071 / T096_DFU	42354C85
Heltec_t1_repeater_lora_ota_no_external_sensors	239A0071 / T1_DFU	FC556FFC
T114 display and without-display lean repeaters	239A0071 / T114_DFU	0C3F2902
Mesh_pocket_repeater_lora_ota_no_external_sensors	239A0071 / MESH_POCKET_OTA	059277F4
KeepteenLT1_repeater_lora_ota_no_external_sensors	239A00B3 / KeepteenLT1_OTA	DB2E7B51
Minewsemi_me25ls01_repeater_lora_ota_no_external_sensors	239A0029 / MX25_DFU	026AA982
ProMicro_repeater_lora_ota_no_external_sensors	239A00B3 / PROM_DFU	AF79E8CC
t1000e_repeater_lora_ota_no_external_sensors	28860057 / T1KE_DFU	E6F5F03F
ThinkNode_M3_repeater_lora_ota_no_external_sensors	239A00DA / TNM3_DFU	0CA41DB2
RAK_3401_repeater_lora_ota_no_external_sensors	239A0029 / 3401_DFU	23818A80
RAK4631 lean repeater and both lean RS232 bridges	239A0029 / 4631_DFU	2D0DF000
GAT562 30S/Tracker Pro/EVB Pro and R1Neo lean carrier aliases	239A0029 / 4631_DFU	2D0DF000
RAK_WisMesh_Tag_repeater_lora_ota_no_external_sensors	239A0029 / RTAG_DFU	C72E9C9C

Board IDs are not globally unique. For generic targets, the signed hardware ID is the exact NUL-padded 32-byte value NRF_BL_<BOARD_ID>_<DEVICE_NAME>. The wire target is the little-endian first four SHA-256 bytes of all 32 padded bytes. The installed and candidate embedded manifest pairs must match exactly. XIAO retains its deployed XIAO_BL_28860044 / XIAO_BL_28860045 identity and raw board-ID target.

The Python reference builder and release tooling audit these boot targets for duplicates and collisions with application target IDs. Generic image parsing can inspect a future canonical identity, but signing/building a package fails until that exact identity is in the qualified inventory.

The no_external_sensors profiles omit optional/add-on sensor and GPS packages to preserve flash headroom. Board-integrated GPS can be retained by a board's recipe. The RAK3401 lean target specifically omits RAK12501/add-on GPS; use the ordinary full-sensor target when that module is required.

Boards with onboard external flash are not silently redirected to internal staging. Mesh Solar, Nano G2 Ultra, T-Impulse Plus, ThinkNode M8, T-Echo Lite/Card, MeshTracker X1, and Wio WM1110 have board-specific QSPI hardware and need a separately matched QSPI path where available. Full Companions, SD/QSPI/ExtraFS roles, Ethernet roles, source-only roles, and unqualified full-sensor roles are excluded.

This internal layout is limited to nRF52840 devices with 1 MiB internal flash, the exact S140 v6/v7 map, and the 40 KiB boot region at 0xF4000..0xFE000. nRF52833 and smaller nRF52 parts cannot provide that map plus a non-overlapping 41,330-byte live staging slot, so configuration fails closed instead of selecting smaller or overlapping geometry.

Explicit install workflow

Check the installed identity and capability marker:

ota bootloader

The response must show a CRC-valid exact identity, ABI 3 or newer, full codec, and exact flags 0x0A for internal shared storage or 0x0E for XIAO QSPI. A bootloader row is visible in ota ls, but it is never autofetched or autoinstalled. Fetch its exact MID, then explicitly arm it:

ota pull <MID8> flash
# wait for ota status to report the download ready
ota bootloader
ota bootloader install <MID8> <HASH16>

Copy both confirmation values from the second ota bootloader response. Ordinary ota install rejects a bootloader package; the bootloader command rejects an application package. The FULL-codec exception exists only for that manual bootloader MID. Ordinary application FULL remains disabled on an internal single-slot node, bootloader autofetch remains off, and a partial bootloader package is not automatically resumed after an application reboot.

Before writing APRV, the application authenticates and authorizes the package: exact v3 geometry, trusted Ed25519 signer, signed/embedded identity, one unambiguous capability marker, embedded CRC, sane vectors, complete Merkle/payload/image hashes, safe live placement, and the typed MID/hash confirmation. OTAFIX consumes that application-written authorization and then independently rechecks the safety/integrity subset: strict v3 structure, canonical identity/capabilities, vectors, full payload SHA, embedded manifest CRC, live EndF no-overlap geometry, page readback, and final copy hash. It does not re-run Ed25519, the signer allowlist, Merkle leaves/root, or the typed operator confirmation. Success is reported as blup:C8.

Failure behavior

The feature fails closed when the MCU/map is wrong, current valid EndF headroom is insufficient, external/ExtraFS storage owns the target, the exact installed capability marker is absent or ambiguous, identity cannot be derived unambiguously, or any package check fails. Before compaction, the application and bootloader are unchanged. OTAFIX consumes the trigger/approval before the first in-place compaction erase, so an interrupted conversion cannot retry a partly converted package; it boots the untouched application and old bootloader instead. Use USB/BLE DFU or SWD for initial provisioning and local recovery.

For XIAO and ordinary external-QSPI details, see nRF52 repeater LoRa OTA with external QSPI.