Add draft: OTA Firmware Updates for Matter Devices via nRF Cloud by franc0is · Pull Request #629 · memfault/interrupt

franc0is · 2026-03-27T20:40:03Z

Fix trailing comma in YAML front matter description (OTA backend, → OTA backend.)
Fix mixed reference-link/footnote syntax ([Memfault OTA documentation][^memfault_ota] → Memfault OTA documentation[^memfault_ota])

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Pull request overview

Adds a new draft blog post describing an approach for performing OTA firmware updates on Matter-over-Thread devices using CoAP blockwise transfers over DTLS with nRF Cloud as the backend, and MCUboot for safe image swapping.

Changes:

Introduces a new draft post detailing an end-to-end OTA architecture (version check, blockwise download, flash streaming, MCUboot swap/confirm).
Includes configuration snippets, illustrative CoAP request/Block2 examples, and a “Trying it out” walkthrough with sample logs.

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_drafts/matter-ota-nrfcloud.md

franc0is · 2026-04-02T19:28:24Z

@copilot apply changes based on the comments in this thread

Copilot · 2026-04-02T20:22:07Z

@copilot apply changes based on the comments in this thread

Applied both changes in commit 5baa440:

Removed trailing comma in the YAML front matter description (OTA backend, → OTA backend.)
Fixed the mixed reference-link/footnote syntax ([Memfault OTA documentation][^memfault_ota] → Memfault OTA documentation[^memfault_ota])

noahp

we don't currently require it, but a nice rewrap with npx prettier --write --prose-wrap=always _drafts/matter-ota-nrfcloud.md would be great, to make it easier to review/read.

great post! ship it 🚢

noahp · 2026-04-03T18:47:37Z

_drafts/matter-ota-nrfcloud.md

+  with nRF Cloud as the OTA backend.
+  on the nRF54LM20 DK.


dangling fragment here?

noahp · 2026-04-03T18:49:40Z

_drafts/matter-ota-nrfcloud.md

+
+`CONFIG_STREAM_FLASH` provides a buffered flash write API that handles page alignment for us. `CONFIG_IMG_MANAGER` and `CONFIG_MCUBOOT_IMG_MANAGER` give us the MCUboot APIs to request an image swap and confirm the new image after boot.
+
+The nRF54LM20's partition layout places the MCUboot primary slot in internal RRAM (the nRF54LM20 uses RRAM, not traditional flash and the secondary slot on external SPI NOR flash (a MX25R6435F). This means the secondary slot erase is slow (~60 seconds for 2 MB), but the primary slot benefits from RRAM's fast write speeds.


Suggested change

The nRF54LM20's partition layout places the MCUboot primary slot in internal RRAM (the nRF54LM20 uses RRAM, not traditional flash and the secondary slot on external SPI NOR flash (a MX25R6435F). This means the secondary slot erase is slow (~60 seconds for 2 MB), but the primary slot benefits from RRAM's fast write speeds.

The nRF54LM20's partition layout places the MCUboot primary slot in internal RRAM (the nRF54LM20 uses RRAM, not traditional flash and the secondary slot on external SPI NOR flash (a MX25R6435F)). This means the secondary slot erase is slow (~60 seconds for 2 MB), but the primary slot benefits from RRAM's fast write speeds.

there's a parenthesis bug here, but not the one you caught ;-). Fixed.

noahp · 2026-04-03T18:52:39Z

_drafts/matter-ota-nrfcloud.md

+    int pos = coap_start_request(coap_buf, sizeof(coap_buf),
+                                 COAP_CODE_GET, 0);
+    coap_buf[0] = 0x48; /* Ver=1, Type=CON, TKL=8 */
+    memcpy(coap_buf + 4, token, 8);
+    pos = 12;


nit- pos return value is overwritten here?

Fixed it - this code isn't the best, I might take one more swing at it.

noahp · 2026-04-03T18:53:54Z

_drafts/matter-ota-nrfcloud.md

+    nrfcloud_send(s, coap_buf, pos);
+
+    /* Receive response, filtering by token to skip stale packets */
+    /* ... (token matching loop omitted for brevity) ... */


maybe also note that error handling is omitted for brevity too, this loop will silently exit if all fail, and i think stream_flash_buffered_write will end up being called with junk

Added a note about it.

noahp · 2026-04-03T18:55:44Z

_drafts/matter-ota-nrfcloud.md

+
+`BOOT_UPGRADE_TEST` tells MCUboot to swap the images, but treat the new image as a **test**. If the new firmware does not explicitly confirm itself, MCUboot will revert to the previous image on the next reboot. This is the safety net for remote devices: a buggy firmware that crashes before confirming will be rolled back automatically.
+
+The image is confirmed early in `main()`, before the application starts:


maybe note that it's unconditionally confirmed here, but could be done after the device has successfully established a connection, for example, in case a rollback is needed

noahp · 2026-04-03T18:56:50Z

_drafts/matter-ota-nrfcloud.md

+
+Block2 over Thread is reliable but not fast. At ~4 KB/s, a 250 KB image takes about a minute. For typical firmware sizes this is fine, but very large images would benefit from a faster transport.
+
+nRF Cloud provides the fleet management features that Matter's DCL lacks: staged rollouts, cohort targeting, and version management with a fast development loop. It offers a free tier for up to 10 devices, and scales at $0.10/device/month.


maybe- soften it to "check nRF Cloud's pricing page for current tiers." so we don't have to update in the future, if pricing changes

gminn

Looks great! I few notes

gminn · 2026-04-03T19:05:41Z

_drafts/matter-ota-nrfcloud.md

+**An OTA backend that speaks UDP.** Our Matter device cannot use HTTP, so we need a backend that supports CoAP over DTLS. I am using nRF Cloud[^nrfcloud] because it provides this out of the box, along with firmware hosting, version management, staged rollouts, and cohort targeting. You could also roll your own.
+
+**Application firmware** on the device that checks for updates, downloads the new image, and writes it to flash. This is the code we will walk through in this post.
+
+**MCUboot**[^mcuboot] is the bootloader. It manages two firmware slots (primary and secondary) and can swap between them safely. If a new firmware fails to boot, MCUboot automatically reverts to the previous version.


nit for readability: bullets

Suggested change

**An OTA backend that speaks UDP.** Our Matter device cannot use HTTP, so we need a backend that supports CoAP over DTLS. I am using nRF Cloud[^nrfcloud] because it provides this out of the box, along with firmware hosting, version management, staged rollouts, and cohort targeting. You could also roll your own.

**Application firmware** on the device that checks for updates, downloads the new image, and writes it to flash. This is the code we will walk through in this post.

**MCUboot**[^mcuboot] is the bootloader. It manages two firmware slots (primary and secondary) and can swap between them safely. If a new firmware fails to boot, MCUboot automatically reverts to the previous version.

- **An OTA backend that speaks UDP.** Our Matter device cannot use HTTP, so we need a backend that supports CoAP over DTLS. I am using nRF Cloud[^nrfcloud] because it provides this out of the box, along with firmware hosting, version management, staged rollouts, and cohort targeting. You could also roll your own.

- **Application firmware** on the device that checks for updates, downloads the new image, and writes it to flash. This is the code we will walk through in this post.

- **MCUboot**[^mcuboot] is the bootloader. It manages two firmware slots (primary and secondary) and can swap between them safely. If a new firmware fails to boot, MCUboot automatically reverts to the previous version.

gminn · 2026-04-03T19:25:33Z

_drafts/matter-ota-nrfcloud.md

+Now the full update - check, erase, download, and reboot:
+
+```
+uart:~$ nrfcloud ota


If you have the timestamps from the zephyr logs, that would be nice to have here so users can see the progression

I'm too lazy to rerun it all :-P

Very fair! A nice to have for sure

gminn · 2026-04-03T19:29:53Z

_drafts/matter-ota-nrfcloud.md

+[00:00:02.145,000] <inf> chip: [SVR]Server initializing...
+```
+
+The whole process takes about 5 minutes.


Could add a little celebration here! I also think it might feel better to have the time discussion here instead of the conclusion (I also added the timestamp callout, in case you add it):

Suggested change

The whole process takes about 5 minutes.

And we're done! 🎉

As the log timestamps show, the whole process takes about 5 minutes. Block2 over Thread is reliable but not fast. At ~4 KB/s, a 250 KB image takes about a minute. For typical firmware sizes this is fine, but very large images would benefit from a faster transport, such as HTTPS.

gminn · 2026-04-03T19:38:11Z

_drafts/matter-ota-nrfcloud.md

+    pos = coap_append_option(coap_buf, pos, sizeof(coap_buf),
+                             &prev_opt, COAP_OPT_MEMFAULT_KEY,
+                             project_key, strlen(project_key));
+


This is an optimization, but the proxy endpoint will now honor response format requests, and plaintext URL would be cleaner to parse than json. You should be able to add this here with:

Suggested change

const uint8_t content_format = 0; /* 0 = text/plain */

pos = coap_append_option(coap_buf, pos, sizeof(coap_buf),

&prev_opt, COAP_OPT_CONTENT_FORMAT,

&content_format, 1);

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Agent-Logs-Url: https://github.com/memfault/interrupt/sessions/d43707dd-81d9-421a-9e40-bb36551e5000 Co-authored-by: franc0is <4192460+franc0is@users.noreply.github.com>

franc0is requested a review from a team as a code owner March 27, 2026 20:40

noahp requested a review from Copilot March 28, 2026 16:07

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Copilot started work on behalf of franc0is April 2, 2026 20:21 View session

Copilot finished work on behalf of franc0is April 2, 2026 20:23

noahp approved these changes Apr 3, 2026

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gminn approved these changes Apr 3, 2026

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franc0is and others added 3 commits April 3, 2026 15:47

Add draft: OTA Firmware Updates for Matter Devices via nRF Cloud

cbd0644

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Fix trailing comma in description and footnote link syntax

0df0399

Agent-Logs-Url: https://github.com/memfault/interrupt/sessions/d43707dd-81d9-421a-9e40-bb36551e5000 Co-authored-by: franc0is <4192460+franc0is@users.noreply.github.com>

Address review comments

47b66f3

franc0is force-pushed the matter-ota-nrfcloud branch from 5ea722c to 47b66f3 Compare April 3, 2026 19:47


		`CONFIG_STREAM_FLASH` provides a buffered flash write API that handles page alignment for us. `CONFIG_IMG_MANAGER` and `CONFIG_MCUBOOT_IMG_MANAGER` give us the MCUboot APIs to request an image swap and confirm the new image after boot.

		The nRF54LM20's partition layout places the MCUboot primary slot in internal RRAM (the nRF54LM20 uses RRAM, not traditional flash and the secondary slot on external SPI NOR flash (a MX25R6435F). This means the secondary slot erase is slow (~60 seconds for 2 MB), but the primary slot benefits from RRAM's fast write speeds.


		`BOOT_UPGRADE_TEST` tells MCUboot to swap the images, but treat the new image as a test. If the new firmware does not explicitly confirm itself, MCUboot will revert to the previous image on the next reboot. This is the safety net for remote devices: a buggy firmware that crashes before confirming will be rolled back automatically.

		The image is confirmed early in `main()`, before the application starts:


		Block2 over Thread is reliable but not fast. At ~4 KB/s, a 250 KB image takes about a minute. For typical firmware sizes this is fine, but very large images would benefit from a faster transport.

		nRF Cloud provides the fleet management features that Matter's DCL lacks: staged rollouts, cohort targeting, and version management with a fast development loop. It offers a free tier for up to 10 devices, and scales at $0.10/device/month.

-The whole process takes about 5 minutes.
+And we're done! 🎉
+As the log timestamps show, the whole process takes about 5 minutes. Block2 over Thread is reliable but not fast. At ~4 KB/s, a 250 KB image takes about a minute. For typical firmware sizes this is fine, but very large images would benefit from a faster transport, such as HTTPS.

+const uint8_t content_format = 0; /* 0 = text/plain */
+pos = coap_append_option(coap_buf, pos, sizeof(coap_buf),
+                         &prev_opt, COAP_OPT_CONTENT_FORMAT,
+                         &content_format, 1);

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franc0is commented Mar 27, 2026 •

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