Add LoRaWAN Class C support

[Beetix]

Implement Class C continuous downlink reception capability:

• Add LMIC_ENABLE_class_c configuration flag in config.h
• Add Class C data structures (lmic_class_c_t) and radio state tracking
• Add RADIO_RXON_C mode for continuous RX on RX2 parameters
• Add os_radio_v2() for async radio operations with job callbacks
• Add os_setIdleJobFunction() for setting callback without scheduling
• Add LMIC_enableClassC() API to enable/disable Class C mode
• Add LMIC_isConfiguredClassC() to check if Class C is compiled in
• Add txrxFlags helpers: LMIC_txrxFlags_isClassC(), LMIC_txrxFlags_setClassC()
• Modify radio IRQ handlers to use LMIC.radio.pFrame for Class C buffer
• Add setupRxClassC() to start continuous RX after TX/RX completion
• Add processRxCDnData() callback for Class C downlink processing
• Report EV_RXCOMPLETE with Class C flag for received downlinks

Class C is disabled by default. Enable with LMIC_ENABLE_class_c=1. After OTAA join, call LMIC_enableClassC(1) to start continuous reception.

Tested on ESP32 (M5Stack Core2) with SX1276 radio and EU868 band.

[terrillmoore]

Many thanks for this contribution!

A few things we'll need before merging:

1. Preserve history: Please layer your changes on top of my branch https://github.com/mcci-catena/arduino-lmic/tree/issue208-578a rather than starting fresh. It looks like your work is substantially based on my code in that branch, and we need to maintain the commit history. Please don't squash the commits.
2. Regression tests: We need compile-time regression tests for Class C enabled builds. I suspect ChatGPT (or Claude Code) should be able to help generate these.
3. Documentation: Your PR doesn't pull forward the documentation and other changes from my branch.
4. After rebasing, we'll need to update all the docs to reflect the Class C API as finally implemented.

Checklist:

• Do not discard history from issue208-578a -- you may need to cherry-pick patches one by one, but with automation that's pretty easy.
• Need to rebase onto the official V5.0.1 branch
• Add regression compile tests for Class C enabled
• Update documentation

I suspect ChatGPT can do all this pretty automatically.

Alternatively, if you'd prefer, you could delegate this to me and I can merge your relevant changes onto my branch.

Thanks again for pushing this forward!

Best regards,
--Terry

[Beetix]

Hi Terry,

Yes, you guessed right. I asked Claude Code to implement class C on the latest version based on the work you had already carried out on branch issue208-578a. I understand that you'd like to keep the history of that work. From what I see there are 36 commits in that branch that are not in v5.0.1 (diverged at commit 8d378ea). Some of which don't seem to concern class C like commit b17b4c7. Is that normal?

I'm happy to help see this through. That being said, if you think it's more appropriate that you take over from here, I have no issue that.

Best regards,
Benjamin

[terrillmoore]

Practically speaking, it will happen sooner if you do the next step. I suspect you run claude less conservatively than I do, I watch it carefully at each step, and that's time consuming. And my time is at a premium.

I also use Claude Code. I believe that if you tell Claude: "OK, that works. Now we need to rebase Terry's branch issue208-578a on the real v5.0.1; then we need compare that to this pull request and figure out whan changed and add those changes to branch isseu208-578a. Preserve all the commit history from branch issue208-578a (do not squash commits)," it will probably work. Anyway, it's easy to try. If claude screws up, it's not very hard to do it manually.

This would make it much easier to review.

Once that's done, one of us can ask Claude to review the documentation and make the appropriate updates, and to create compilation test cases.

[terrillmoore]

By the way -- the commits in the branch that are not class C were other bugs that I found in my review. My intention was to rebase once I got done -- keeping commit history and having lots of commits help you do this. If we can get to the point of having a branch with the full commit history, we can then ask claude to rearrange the order of the commits to keep non-Classs-C things separate. It's possible that I already cherry-picked non-class-C things. I think Claude will figure that out.

We've been doing group Claude sessions in The Things Network New York meetings recently; if you wanted to join a Teams meeting we could do this jointly. Or just continue via email like this. Thing is I need to watch it working to figure out what needs to be in CLAUDE.md and other project instructions to let it do the best job -- it's hard to do that via comments in a commit history.

[Beetix]

Ok, so all commits even the ones that are not Class C related should be rebased on v5.0.1 right?

I'll go ahead and try this with the help of your instructions.

I'm also interested in joining one of your Claude group sessions. Could you please send me the details via mail (in commit)?

[terrillmoore]

I would first ask claude to rebase https://github.com/mcci-catena/arduino-lmic/tree/issue208-578a onto master. (This will remove all changes that I already incorporated into 5.0.1.) Then ask it to compare the result to what you have, and incorporate fixes from your branch into the new branch. Code is pretty capable; if you do this from the same session (use claude --resume) that generated the changes, it will figure out what you're doing and fill in the blanks. You can make a PDF of this email thread and ask Claude to read it for context.

Best way to join meetings is to get into the slack for thethings.nyc -- normally that needs an email address. My address is already published: terry@thethings.nyc -- if you email me, I'll add you to the slack.

[Beetix]

I proceeded as instructed. Here is the result after force pushing the changes.

An issue was found with the SX126x driver. Should that be fixed in this PR too?

[terrillmoore]

This is very helpful! Now I can see from the log that we're also merging the secure element changes -- that's not a bad idea at all. I think it also merges the doxygen setup.

Re the bug in the SX126x driver: I think it's ok to push the change, as long as an issue is created and the commit message for the fix starts with "Fix #{issue-num}: ..." so that the issue will be autoclosed when we merge.

While you're at it, can you ask ask Claude why Github is not running the CI tests against this branch. There's a config problem of some kind. I found the button I had to push, so the existing CI tests are now being run. We'll need to review results.

Since the main doc is a word doc, I may use CoWork to try to update the word doc.

(What happens with AI is that you can do so much more, that the work of prompting expands to fill the available time. We should ask Claude CoWork to study all of the documentation, and reorganize and unify so that it's easier for people to get started; and to look at the issue history to write up a troubleshooting guide. Although for troubleshooting, people probably should just ask Claude at this point.)

Thanks!

[terrillmoore]

Looks like AVR failed, probably due to code size. We could probably ask Claude Code to look into it. We might need to make a config change for the AVR CI builds..

[Beetix]

Re the bug in the SX126x driver: I think it's ok to push the change, as long as an issue is created and the commit message for the fix starts with "Fix #{issue-num}: ..." so that the issue will be autoclosed when we merge.

Created issue #1021 and pushed the fix

[Beetix]

Looks like AVR failed, probably due to code size. We could probably ask Claude Code to look into it. We might need to make a config change for the AVR CI builds..

Strange... The tests pass locally on my end

[Beetix]

I had Claude look into the AVR failing test issue:

The compliance example also fails on v5.0.1 - this is a pre-existing bug in the upstream repository, not related to my SX1262 fix.

The issue is that compliance-otaa-halconfig.ino contains STM32-specific code (RTC_HandleTypeDef, HAL_RTC_* functions) that isn't properly guarded with architecture checks. When compiled for AVR, these symbols
don't exist.

Summary:

• The AVR CI failure for compliance-otaa-halconfig is a pre-existing upstream bug
• It fails on both v5.0.1 and the feature branch identically
• My SX1262 fix only touched radio_sx126x.c and doesn't affect AVR/SX1276 builds at all

The CI workflow from mcci-catena-ci repo tests this example, but the local ci/platformio.sh script (which passes) doesn't. This is why it wasn't caught before.

Would you like me to fix the compliance example's architecture guards, or should we note this as a known issue to address separately?

How do you want to proceed?

[ychlc]

Hey all, a few things:

A. Bumping this, as it looks like it's super close to getting merged, which would be fantastic!

EDIT: After writing everything below, I realized...are we supposed to be using LMIC.classC.frame when processing class C data, and not LMIC.frame? The doc/CLASS-C.md uses LMIC.frame:

case EV_RXCOMPLETE:
            Serial.print("Received ");
            Serial.print(LMIC.dataLen);
            Serial.println(" bytes");

            if (LMIC_txrxFlags_isClassC(LMIC.txrxFlags)) {
                Serial.println("(Class C downlink)");
            }

            // Process received data
            for (int i = 0; i < LMIC.dataLen; i++) {
                Serial.print(LMIC.frame[LMIC.dataBeg + i], HEX);
                Serial.print(" ");
            }
            Serial.println();
            break;

But everything works totally fine if we instead use:

Serial.print(LMIC.classC.frame[LMIC.dataBeg + i], HEX);

Original comment:

B. On that note, I have been testing this branch and appear to have found a bug(?) with the class C message decoding. Unfortunately, I don't have a great understanding of the inner workings here, so pardon my ignorance. If I should move this to an issue, let me know; I'm not a big contributor on GH.

In processRxCDnData(), the class C frame is copied to the regular frame:

os_copyMem(LMIC.frame, LMIC.classC.frame, LMIC.dataLen);

However, when processing the downlink:

if (LMIC.dataLen > 0 && decodeFrame()) {
...

decodeFrame() references LMIC.radio.pFrame as the frame, rather than LMIC.frame:

...
xref2u1_t d = LMIC.radio.pFrame;
...

This leads to the payload being incorrect. That's the part I'm unsure about. I'm hoping it'll be a quick fix for @Beetix, as it causes the payload data you process in a RX_COMPLETE callback to be incorrect.

I debugged the frames just before decoding, but I don't know enough to know why, even though pFrame appears to be the classC frame, the "correct" frame to decode is LMIC.frame.

radio.pFrame=0x20001ad0 frame=0x200019b8 classC=0x20001ad0

As a temporary workaround, I added the following in processRxCDnData():

...
if (LMIC.dataLen > 0) {
        os_copyMem(LMIC.frame, LMIC.classC.frame, LMIC.dataLen);
        LMIC.radio.pFrame = LMIC.frame; // <--
    }
...

Of course, after adding the line above, debugging the frames is as expected:

radio.pFrame=0x200019b8 frame=0x200019b8 classC=0x20001ad0

And my payload is now decoded correctly. Instead of getting random integers from my payload (due to it still being encrypted?), I get my payload value of 1 when I send a downlink payload with a hex value of 01.

Otherwise, this branch and class C work amazingly! Thanks for all the work here.

[Beetix]

Hi @ychlc,

Your finding is correct! Thank you for your contribution to this PR. I've commited and pushed the modification you propose.

I'm still waiting for @terrillmoore to respond so it can me merged. Fingers crossed!

[terrillmoore]

Hi all, I’m hoping to review and push this along this weekend. Sorry for the delay.

…

--Terry From: Benjamin Freeman ***@***.***> Sent: Friday, March 13, 2026 18:38 To: mcci-catena/arduino-lmic ***@***.***> Cc: Terry Moore ***@***.***>; Mention ***@***.***> Subject: Re: [mcci-catena/arduino-lmic] Add LoRaWAN Class C support (PR #1019) <https://avatars.githubusercontent.com/u/10374047?s=20&v=4> Beetix left a comment (mcci-catena/arduino-lmic#1019) <#1019 (comment)> Hi @ychlc <https://github.com/ychlc> , Your finding is correct! Thank you for your contribution to this PR. I've commited and pushed the modification you propose. I'm still waiting for @terrillmoore <https://github.com/terrillmoore> to respond so it can me merged. Fingers crossed! — Reply to this email directly, view it on GitHub <#1019 (comment)> , or unsubscribe <https://github.com/notifications/unsubscribe-auth/AETP73YPL4435R6XQ2TU6EL4QSEUHAVCNFSM6AAAAACSVTUW7CVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DANJYGQ2TGMRSHA> . You are receiving this because you were mentioned. <https://github.com/notifications/beacon/AETP733NJ5NFYPFLUBE22C34QSEUHA5CNFSM6AAAAACSVTUW7CWGG33NNVSW45C7OR4XAZNMJFZXG5LFINXW23LFNZ2KUY3PNVWWK3TUL5UWJTXR44KOY.gif> Message ID: ***@***.*** ***@***.***> >