docs(docs): subedit

docs/en/dronecan/index.md

@@ -6,7 +6,7 @@
 
 - DroneCAN is not enabled by default, and nor are specific sensors and features that use it.
   For setup information see [PX4 Configuration](#px4-configuration).
-- PX4 requires an SD card to enable dynamic node allocation and for firmware update.
+- PX4 requires an SD card to enable dynamic node allocation and for [firmware update](#firmware-update).
   The SD card is not used in flight.
 
 :::
@@ -310,34 +310,44 @@ Most DroneCAN nodes require no further setup, unless specifically noted in their
 ## Firmware Update
 
 PX4 can upgrade device firmware over DroneCAN.
-On boot the flight controller scans for firmware binaries, migrates them to the firmware directory, and automatically transfers the firmware to any connected node whose version does not match.
 
-### Placing Firmware Files
+::: info
+PX4 identifies valid firmware binaries (`.bin`) based on the presence of an **APDescriptor** — a metadata block embedded in the `.bin` file that contains the target board ID, firmware version, and a checksum.
+PX4 uses this descriptor to match each binary to the correct node and to determine whether an update is needed.
+:::
 
-Place firmware binaries (`.bin` files with a valid APDescriptor) in one of these locations on the SD card before rebooting:
+### Firmware Directories
+
+Place firmware binaries in one of these locations on the SD card before rebooting:
 
 - **SD card root** (`/fs/microsd/`): Simplest option for manual updates.
-- **Staging directory** (`/fs/microsd/ufw_staging/`): Preferred for remote/programmatic updates. The directory is swapped in atomically at boot, avoiding write conflicts if files are uploaded while the vehicle is running.
+- **Staging directory** (`/fs/microsd/ufw_staging/`): Preferred for remote/programmatic updates.
+  Files are moved to `/fs/microsd/ufw/` at boot before any node is flashed, avoiding write conflicts if firmware is uploaded while the vehicle is running.
 
-On boot, the UAVCAN server scans both locations, reads the board ID from the APDescriptor of each file, and copies it to `/fs/microsd/ufw/<board_id>.bin`. The source file is then deleted. Any connected node whose running version does not match is then flashed over the CAN bus.
+On boot, PX4 scans both locations, reads the board ID from the _APDescriptor_ of each file, and copies them to `/fs/microsd/ufw/<board_id>.bin`.
+The source file is then deleted.
+Any connected node whose running version does not match is then flashed over the CAN bus.
 
 ### Firmware Database
 
-A flat-file database at `/fs/microsd/ufw/FW.db` maps each board ID filename to the original filename that was installed. Stale entries are removed automatically on every boot. Example entry:
+A flat-file database at `/fs/microsd/ufw/FW.db` maps each board ID to the original firmware filename that was installed.
+Stale entries are removed automatically on every boot.
+Example entry:
 
-```
+```txt
 122.bin=122-1.17.63eeff1a.uavcan.bin
 ```
 
 ### Remote Update
 
-Firmware can be delivered remotely by bundling `.bin` files into an update archive. An external update tool can extract the archive on the target and copy the CAN firmware files into `/fs/microsd/ufw_staging/`. They are then picked up on the next boot.
+Firmware can be delivered remotely by bundling `.bin` files into an update archive.
+An external update tool can extract the archive on the target and copy the CAN firmware files into `/fs/microsd/ufw_staging/`. They are then picked up on the next boot.
 
 Before uploading, the tool can read `/fs/microsd/ufw/FW.db` to check which firmware is already installed and skip files that haven't changed, reducing transfer size.
 
 `upload_skynode.sh` handles the bundling via the `--ext-fw` flag (repeatable for multiple nodes):
 
-```
+```sh
 ./Tools/auterion/upload_skynode.sh \
   --ext-fw=build/auterion_canio_default/auterion_canio_default.uavcan.bin
 ```