--- title: Using IAP Firmware Update description: Learn how to update your host MCU firmware using Notehub via traditional IAP (In Application Programming) methods. source_url: https://dev.blues.io/notehub/host-firmware-updates/iap-firmware-update/ canonical_url: https://dev.blues.io/notehub/host-firmware-updates/iap-firmware-update/ markdown_url: https://dev.blues.io/notehub/host-firmware-updates/iap-firmware-update.md --- # Using IAP Firmware Update > **Warning:** > > If you're using a compatible STM32, ESP32, or nRF microcontroller, we highly recommend using [Notecard Outboard Firmware Update](https://dev.blues.io/notehub/host-firmware-updates/notecard-outboard-firmware-update.md) to perform DFU operations as it's more reliable, secure, and you can roll back any unintended changes. IAP (In Application Programming) is a more traditional form of DFU that performs firmware updates while the program is running. > Read more about IAP vs ISP (In System Programming) in [this kanda.com article](https://www.kanda.com/blog/general/isp-iap-programming-processes/). ## Upload Host MCU Firmware 1. Select **Settings > Firmware** from the left navigation bar and click **Upload Firmware**. ![Upload firmware option](https://dev.blues.io/images/notehub/settings_upload_firmware.png?v=509f88fe) 2. Upload your new firmware binary with the form provided. ![Upload page](https://dev.blues.io/images/notehub/firmware_upload_page.png?v=1d7d7d45) ## Deploy Firmware 1. Select **Devices** from the left navigation bar, select a device from the list of devices in the **Host Firmware** tab, and then click **Update**. ![Device selected from list](https://dev.blues.io/images/notehub/device_select_host_fw.png?v=a16c8fa5) 2. Select the firmware you wish to apply from the list of available firmware, and click **Apply**. ![Update host firmware button](https://dev.blues.io/images/notehub/select_host_firmware.png?v=f286fbb2) 3. Consult [Notecard API Requests for DFU](https://dev.blues.io/notehub/host-firmware-updates/notecard-api-requests-for-dfu.md#obtaining-firmware-download-status) to configure how Notecards process DFU requests. ## Implementing IAP on the Host Once a firmware binary has been uploaded to Notehub and a DFU action has been applied to a device, the host MCU is responsible for polling the Notecard, transferring the binary in chunks, validating it, and rebooting into the new image. Each individual API request used during this flow is documented on [Notecard API Requests for DFU](https://dev.blues.io/notehub/host-firmware-updates/notecard-api-requests-for-dfu.md); the steps below show how those requests fit together end-to-end. A typical host DFU loop, called periodically, performs the following actions: 1. Issues a `dfu.status` request to the Notecard and checks the `mode` field in the response to determine whether a firmware image is being downloaded by the Notecard (`downloading`), has finished downloading and is ready for installation (`ready`), failed to download (`error`), or no new firmware is available (`idle`). Only the `ready` mode should advance the loop. 2. Prepares the host's secondary (inactive) partition or update region to receive the incoming binary. Do this *before* entering DFU mode, so that slow work like erasing a large flash region doesn't run against the DFU-mode timeout described below. 3. Once a new firmware binary has been downloaded and any pending network activity completes, issues a `hub.set` request with `mode` set to `dfu`, signaling to the Notecard that the host is ready to retrieve firmware. 4. Confirms the Notecard has finished entering DFU mode by issuing a `dfu.get` request with `length` set to `0`, which checks readiness without transferring data. The Notecard has to finish any in-progress network activity and close its connection first, so this request returns a `{dfu-not-ready}` error until that completes — retry it until it succeeds rather than assuming a fixed delay. See [Ensuring Host DFU Mode is Active](https://dev.blues.io/notehub/host-firmware-updates/notecard-api-requests-for-dfu.md#iap-only-ensuring-host-dfu-mode-is-active). 5. Performs a series of `dfu.get` requests to obtain the host firmware binary in chunks, incrementing `offset` by the requested `length` on each request. Each chunk is CRC-validated and written to the host's update region using whatever flash-write or OTA utility the host platform provides. 6. After the entire binary is retrieved, issues another `hub.set` with `mode` set to `dfu-completed` to indicate that the Notecard can resume its normal operations. 7. Performs a final CRC check, comparing the CRC of the downloaded firmware to the `body.crc32` value provided by Notehub in the initial `dfu.status` response. (The same `body` object also carries `length` and `md5` values you can verify against.) If the values match, marks the new image as the boot target. 8. Issues a `dfu.status` request with the `stop` field set to `true`. Upon receipt, the Notecard removes the firmware binary from its internal storage. 9. Restarts the host and begins running the new firmware. > **Warning:** > > The Notecard does not stay in DFU mode indefinitely. If 15 minutes elapse without a `dfu.get` request, the Notecard leaves DFU mode on its own and resumes normal operation, and any in-progress transfer will start failing. If your host aborts partway through the update—because a `dfu.get` fails, or the CRC check does not match—make sure your error path still takes the Notecard back out of DFU mode with a `hub.set` request, and clears the DFU state so Notehub reflects the outcome. See [Clearing DFU State](https://dev.blues.io/notehub/host-firmware-updates/notecard-api-requests-for-dfu.md#clearing-dfu-state) for the requests to use. > **Tip:** > > For a complete reference implementation in C++ for the ESP32, see the [note-samples ESP32 DFU example](https://github.com/blues/note-samples/tree/main/esp32-dfu) on GitHub. The `dfu.cpp` file in that repository implements the full loop above and can be adapted to other host platforms. [Notecard Outboard Firmware Update](https://dev.blues.io/notehub/host-firmware-updates/notecard-outboard-firmware-update.md "Notecard Outboard Firmware Update") [Notehub API Requests for DFU](https://dev.blues.io/notehub/host-firmware-updates/notehub-api-requests-for-dfu.md "Notehub API Requests for DFU")