Notecard Firmware Update Issue

Notecards that performed an over-the-air Notecard firmware update (DFU) via Notehub to Notecard firmware version are subject to an issue that prevents further over-the-air updates.

If you received a Notecard from Blues with this version installed already, you should not experience this problem. If you have questions about your specific Notecard and if it’s firmware version is subject to this issue, please reach out to

Issue Behavior

If a Notecard is running a firmware image that is subject to this problem, when the Notecard receives a request to download a new firmware image, either for the Notecard or the host MCU, the Notecard will get stuck in a loop attempting to download and store 0 bytes of the image. This happens in a repeated fashion. The Notecard will not connect to the network until it resets. A reset will abort the DFU process and re-enable network connectivity.

On Notehub the firmware download progress will be stuck at 0%. And should be updated with error message that the DFU has been aborted once the Notecard restarts and connects to Notehub.

We know this affects the image of Notecard firmware that had been published on Notehub. It did not affect Notecards that were shipped with this image to customers from Blues.

Root Cause

The image for that was published on Notehub was corrupted as part of the firmware build process.


Our analysis of devices connecting to Notehub shows that very few devices are affected by this issue. If that changes, we will update this post.

We are reaching out to Notehub users we’ve identified that are affected by this issue.

If you are concerned about whether or not your devices are affected by this issue, please reach out to

Corrective Actions

Here’s what we’ve been doing to address this issue and prevent it from occurring in the future.

  1. We have unpublished and removed Notecard firmware from Notehub
  2. We have published an uncorrupted build on Notehub, and incremented the build number to
  3. We have updated our firmware image repository with this version as well to maintain consistency between images on the Notehub and the image repository Notecard Firmware Updates - Blues Developers
  4. We are updating our build, release, and publish process to avoid this type of issue going forward
  5. We are adding defensive logic to future Notecard firmware releases to prevent looping on a 0 byte download.

Issue Mitigation Strategies

If you have an affected device, here are some strategies to mitigate or resolve the problem posed by the corrupted firmware image.

  1. Manually update the Notecard firmware with the uncorrupted version.
    This will correct the problem, not just avoid it. This is only possible with physical access to the device. Use notecard-$20230511152328.bin or later Notecard Firmware Updates - Blues Developers Follow the manual update process here: Manually Updating Notecard Firmware v5.1.1 and later via USB

    If you require assistance, please reach out to

  2. Disable firmware updates for the specific devices that are affected.

    This is to prevent the case where a firmware update is unintentionally applied to the device, and the firmware download issue inhibits network communication. This might not be effective in cases where the host MCU determines if firmware download is permissible.

    For assistance on this option, please reach out to

  3. Set the _restart_no_activity_hours environment variable from Notehub.
    Understanding Environment Variables - Blues Developers

    This is a fallback if the firmware updates are still enabled, and the affected Notecards are requested to update either Notecard or Host MCU firmware. It will force a Notecard to restart if it hasn’t connected to Notehub after a timeout period. This is to mitigate network connectivity inhibition in the event of an unintentional over-the-air firmware update.

If the above strategies don’t work for your situation, you need assistance determining the appropriate strategy, or implementing the strategy don’t hesitate to reach out to

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