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Updating Here4 GNSS Firmware

This guide walks through the only reliable method we found for updating firmware on a CubePilot Here4 RTK GNSS module (CAN node) when your flight controller normally runs PX4.

Read this whole document once before starting. The process is safe and repeatable if followed exactly, but skipping or reordering steps can leave the Here4 in an unusable (though recoverable) state.

Why this process is necessary

  • You cannot use QGroundControl (QGC) to flash Here4 firmware. Period. QGC has no reliable CAN-node firmware-push tool for this device.
  • PX4 does support flashing CAN peripherals directly via an SD card (official PX4 docs) — but in practice, this gets the Here4 stuck mid-update. It is not unrecoverable, but it will leave your GPS non-functional until you complete the procedure below.
  • Mission Planner (the tool that does reliably flash this device) is built around ArduPilot, not PX4. Its DroneCAN detection does not work reliably against a PX4 flight controller — even with a known-good, freshly-purchased Here4 unit.
  • The practical fix: temporarily flash ArduPilot onto your flight controller, use Mission Planner to update the Here4, then flash PX4 back. The Here4's firmware lives entirely on its own separate microcontroller — flashing ArduPilot onto your flight controller does not touch the Here4 at all, it just changes who's "talking" to it on the CAN bus.
  • This tutorial may be relevant if the RTK setup you are using isn't working as expected.

Requirements

  • A Windows computer. Mission Planner is stated to also work on Linux/Android, but in our testing it fails to connect on Linux even after the commonly suggested sudo apt install mono-complete fix. Don't waste your time on Linux — use Windows.
  • Mission Planner installed.
  • QGroundControl installed (you already have this for normal PX4 operation).
  • A CubePilot Blue flight controller (standard Cube carrier board).
  • A microUSB cable.
  • The quadcopter's battery must NOT be connected for the entire process below. Everything is powered via USB only.

Throughout this guide, "reboot" means: unplug the microUSB cable, wait a few seconds, then plug it back in. Do not connect the battery at any point during this procedure unless explicitly told to.

Step 0: Back up your PX4 parameters

Before touching anything, export your current PX4 parameter file from QGC (Vehicle Setup → Parameters → Tools → Save to file). You'll need to reconfigure PX4's DroneCAN/GPS parameters from scratch after this process (ArduPilot and PX4 use completely separate parameter systems — nothing carries over automatically), and having your old values on hand makes that faster.

Step 1: Check your wiring

The Here4 connects to the flight controller over CAN using a 3-wire (white/green/blue) cable — plug this into CAN 1 on the CubePilot Blue.

Ignore the red and black cable entirely. Leave it unplugged from everything for this whole process.

Step 2: Flash ArduPilot onto the flight controller

Using QGC (while still connected to the quad as normal, over USB or your telemetry link):

  1. Go to the firmware flashing screen and select ArduCopter. The latest stable version is fine.
  2. Let it flash and reboot as prompted.

Your flight controller is now running ArduPilot instead of PX4. This is temporary — you'll flash PX4 back in the final step.

Step 3: Set the required ArduPilot CAN/GPS parameters

Physical state at this point: quad powered via microUSB only, no battery connected, Here4 wired to CAN1 as in Step 1.

  1. Open Mission Planner and connect over USB (not radio/telemetry) — click Connect in the upper-right corner.
  2. In the parameter list, set the following:
Parameter Value
CAN_D1_PROTOCOL 1
CAN_D2_PROTOCOL 1
CAN_P1_DRIVER 1
CAN_P2_DRIVER 1
GPS_TYPE 9
NTF_LED_TYPES 231
CAN_D1_UC_OPTION 1

CAN_D1_UC_OPTION is the critical, easy-to-miss step. The official Here4 manual (docs.cubepilot.org) does not mention it, but without it, the Here4 will not appear in Step 4 below.

  1. Click Write Params.
  2. Reboot the quad (unplug/replug the microUSB cable).
  3. Reconnect in Mission Planner and double-check every parameter above stuck. Mission Planner's parameter display is not always trustworthy immediately after a write — verify by reading them back after the reboot, not just trusting the write confirmation.

Important: After this reboot, CAN_D1_UC_OPTION will read back as 0 again. This is expected and correct — it means the CAN register did its job of resetting so ArduPilot can now see the Here4. Do not "fix" this back to 1; leave it as the post-reboot value shows.

Step 4: Confirm the Here4 is detected

Physical state: unchanged from Step 3 (USB only, no battery).

  1. In Mission Planner, go to Setup → Optional Hardware → DroneCAN/UAVCAN.
  2. Select the entry corresponding to CAN1. The Here4 manual calls this MAVLinkCAN1, but as of September 2026 Mission Planner has renamed this option — look for whichever entry corresponds to CAN1 rather than matching the exact old name.
  3. Click Connect — not the Connect button in the upper-right corner. This is a separate button in the top-middle of the DroneCAN/UAVCAN screen itself.

You should now see three entries appear: - org.missionplanner - org.ardupilot0 - org.com.cubepilot.here4

If you only see org.missionplanner and nothing else, stop and troubleshoot before proceeding — this means the Here4 isn't visible on the bus yet. Common causes: still running PX4 (Step 2 wasn't completed/saved), CAN_D1_UC_OPTION wasn't set before the reboot in Step 3, or a wiring issue from Step 1.

Step 5: Get the correct firmware file

  1. Go to github.com/CubePilot/GNSSPeriph-release/releases.
  2. Download the latest STABLE release — do not pick a pre-release.
  3. From that release, download the .bin file. Ignore any .apj or .elf files if present in the release assets — .bin is the correct format for flashing this CAN peripheral (.apj is used for flight-controller firmware, and .elf is a debug-symbols build for use with a hardware debug probe — neither applies here).

Step 6: Flash the Here4

  1. Back in Mission Planner's DroneCAN/UAVCAN screen (Step 4), find the org.com.cubepilot.here4 entry.
  2. Click Menu → Update.
  3. When asked whether to search the internet for the latest firmware, click No. In our testing, this internet search can return a mismatched or even older version specifically for the Here4 — always supply the file you downloaded directly from CubePilot's GitHub in Step 5 instead.
  4. When prompted, browse to and select the .bin file you downloaded.
  5. Let it run. Do not unplug the USB cable or interrupt this process.

Reading the Here4's LED during this step

This isn't documented well anywhere else, so pay attention to the LED on the Here4 itself while it updates:

  • Slowly pulsing white — normal. The update is in progress; let it finish.
  • Solid (steady, non-pulsing) white — this may indicate the update has failed or the unit is stuck in a bad state. If you see solid white rather than a pulse, stop and don't keep power-cycling repeatedly hoping it resolves on its own.

If the update genuinely stalls (no LED change, no progress) for an extended period — more than roughly 10 minutes with zero change — treat it as stuck rather than "still working," and move to the fallback below rather than continuing to wait indefinitely.

Step 7: Verify the update succeeded

After Mission Planner reports the update as complete:

  1. In the DroneCAN/UAVCAN screen, refresh/reconnect and confirm the Here4's reported firmware version now matches the release you selected in Step 5.
  2. Confirm the LED has settled to its normal steady/breathing state (not pulsing, not solid white).

Step 8: Return to PX4

The Here4 is now updated and independent of whatever the flight controller runs — but your quad still needs to fly on PX4.

  1. In QGC, flash PX4 back onto the flight controller (whatever version you were running before — we used v1.16.2).
  2. Let the flight controller boot on PX4's own default parameters first — do not immediately load your saved .params file from Step 0. Reflashing firmware families back and forth can leave the parameter set in an inconsistent state if you load a saved file over it too quickly. Let PX4 come up clean once, then load your saved parameters as a deliberate, separate step afterward.
  3. Re-set/verify your PX4 DroneCAN/GPS parameters. These do not carry over from ArduPilot. At minimum, revisit:
  4. UAVCAN_ENABLE
  5. UAVCAN_SUB_GPS
  6. UAVCAN_PUB_RTCM (if using RTK corrections)
  7. EKF2_GPS_CTRL

Use your Step 0 backup as a reference for the values you had before. 4. Confirm PX4 detects the Here4 again: open the MAVLink Console and run uavcan status — the Here4's node should show up with mode OPERAT.

⚠️ Double-check your parameters actually loaded correctly

Do not trust a loaded .params file blindly — verify it, parameter by parameter, before you fly. In our case, after loading our saved parameters back in, several CA_ (control allocation / motor mixer) parameters silently came back wrong — for example, a value that should have been 0.25 loaded as 1.00 instead. We didn't catch this immediately, and it made the quad unflyable (the motor mixer was effectively miscalibrated). There was no obvious error or warning — the parameter file simply didn't apply cleanly across the reflash. Spot-check your critical parameters (especially anything under CA_) against your Step 0 backup after loading, rather than assuming the load succeeded just because it didn't throw an error.

Recalibrate your sensors before flying

After all of the above, recalibrate the compass — this is required, not optional, after this process. In our case, one indoor calibration attempt wasn't enough to clear the errors; we had to calibrate the compass a second time outdoors before it stuck cleanly. If you see persistent compass-related errors after an indoor calibration, don't assume something else is broken — try again outside first.

For good measure, we also recalibrated Level Horizon, the accelerometer, and the gyroscope (i.e., all onboard sensors) at the same time, rather than just the compass alone. After doing all of this, the quad flew normally.

Only once you've verified your parameters, recalibrated all sensors, and confirmed a healthy GPS fix should you consider reconnecting the battery and proceeding to normal flight testing. You can put the GPS back on the CAN extender rather than CAN1.

Fallback: if Mission Planner still won't cooperate

If you hit a wall anywhere in the above — Mission Planner won't detect anything even after correctly following every step, or the Here4 ends up in the solid-white stuck state — the more robust (but slightly more involved) option is to bypass Mission Planner entirely:

  1. Buy a USB-to-CAN adapter (an adapter running "slcan" firmware, such as a CANable-style adapter, is a common and inexpensive choice).
  2. Wire the adapter's CAN-H/CAN-L leads directly onto the CAN bus, in parallel with the existing Here4-to-flight-controller wiring (CAN is a shared bus, so tapping in alongside the existing connection is fine).
  3. Install and run dronecan_gui_tool (free, cross-platform) pointed at that adapter.
  4. Flash the same .bin file from Step 5 through this tool instead of Mission Planner.

This talks to the CAN bus directly at the protocol level, with no dependency on either Mission Planner's or QGC's flakier CAN-over-MAVLink bridging — it's the method a PX4 core developer has used to resolve this exact class of issue in the past.