CRSF: Allow future use of unused bits in the "Arming status byte" by mha1 · Pull Request #7022 · EdgeTX/edgetx

mha1 · 2026-01-22T20:18:24Z

This PR allows future use of the currently unused status bits in the byte we use to communicate the commanded arming status to ExpressLRS modules if we ever have a need for them. The changes are fully backward compatible with the existing V2.11 and V2.12 implementation for communicating the commanded arming status to ExpressLRS modules. It is also compatible with modules using ExpressLRS V3 firmware.

Summary of changes:

sends status byte with every CRSF 0x16 RC Channels packet. Note: the TBS CRSF V3 specification allows sending extra fields. CRSF V3 Frame Details: "size may be bigger than expected frame of given type. This should not be a reason to count the frame invalid. Frame receiver should just ignore extra fields.". ExpressLRS pre-V4 firmware ignores the field and will use CH5 Arming.
determines arming method and status using bit 0 and 1 of the status byte

makes status byte bits 2 to 7 available for future use

This complements the changes made to V4 in ExpressLRS/ExpressLRS#3470 and is fully backwards compatible to the existing implementation

Summary by CodeRabbit

Bug Fixes
- Fixed Crossfire CHANNELS frame structure to use a consistent fixed-length payload with dedicated status byte
- Improved arming status reporting in Crossfire protocol to properly reflect armed state based on configuration

gagarinlg

what is this part of the code for?

gagarinlg · 2026-05-18T09:08:20Z

+  // Example: flag crsf errors to ELRS in bit 2 for resending linkstats
+  //
+  //extern bool crsfErrorFlag;
+  //if(crsfErrorFlag) {
+  //  *buf |= 0x04;                                   // flag crsf error
+  //  crsfErrorFlag = false;
+  //}
+
+  buf++;


what is this for?

This is indeed example code on how the spare bits can be used, e.g. for debugging. I'll remove the dead code.

Copilot

Pull request overview

This PR updates CRSF channel frame generation so the status byte is always appended, enabling arming-mode signaling while leaving higher bits available for future status flags.

Changes:

Always sends a 25-byte CRSF channel frame payload including the extra status byte.
Encodes Switch-mode armed state in bit 0 and CH5 arming mode in bit 1.
Updates CRC calculation to include the always-present status byte.

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

  uint8_t * buf = frame;
  *buf++ = MODULE_ADDRESS;
-  *buf++ = 24 + lenAdjust;      // 1(ID) + 22(channel data) + (+1 extra byte if Switch mode) + 1(CRC)
+  *buf++ = 25;                  // 1(ID) + 22(channel data) + 1(extra status byte) + 1(CRC)


+  // Example: flag crsf errors to ELRS in bit 2 for resending linkstats
+  //
+  //extern bool crsfErrorFlag;
+  //if(crsfErrorFlag) {
+  //  *buf |= 0x04;                                   // flag crsf error
+  //  crsfErrorFlag = false;
+  //}
+


coderabbitai · 2026-05-18T12:24:54Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: c7cc18bc-7954-4fbf-a3b7-2ac54497ada0

📥 Commits

Reviewing files that changed from the base of the PR and between de5f4eb and debd129.

📒 Files selected for processing (1)

radio/src/pulses/crossfire.cpp

📝 Walkthrough

Walkthrough

createCrossfireChannelsFrame now builds CHANNELS frames with fixed 25-byte payload including a status byte. Frame header construction and channel-assembly points are adjusted; status byte encodes armed state (Switch mode) or CH5 mode flag, with CRC8 recomputed for the new length.

Changes

Crossfire Frame Status Byte Integration

Layer / File(s)	Summary
Frame structure with status byte assembly `radio/src/pulses/crossfire.cpp`	Frame header allocates fixed 25-byte payload; channel-ID assembly offset adjusted. Status byte assembled after channel packing: reflects commanded armed status in Switch mode, or constant CH5 indicator (0x02) otherwise. CRC8 length updated to match new frame format.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: allowing future use of unused bits in the arming status byte while maintaining backward compatibility.
Description check	✅ Passed	The description covers the key aspects including backward compatibility, the status byte implementation, and a summary of changes with visual documentation.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

Create PR with unit tests

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

mha1 added 4 commits January 15, 2026 18:44

initial commit

1b7fb27

make flagging crsf errors an example

a6406bc

updated comment on bit meanings

de13f39

fix merge error

2ca8d26

gagarinlg requested a review from Copilot May 18, 2026 09:07

Copilot started reviewing on behalf of gagarinlg May 18, 2026 09:08 View session

gagarinlg reviewed May 18, 2026

View reviewed changes

Copilot AI reviewed May 18, 2026

View reviewed changes

removed dead example code

debd129

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

CRSF: Allow future use of unused bits in the "Arming status byte"#7022

CRSF: Allow future use of unused bits in the "Arming status byte"#7022
mha1 wants to merge 5 commits into
EdgeTX:mainfrom
mha1:PR_use_more_status_bits

mha1 commented Jan 22, 2026 •

edited by coderabbitai Bot

Loading

Uh oh!

gagarinlg left a comment

Uh oh!

gagarinlg May 18, 2026

Uh oh!

mha1 May 18, 2026 •

edited

Loading

Uh oh!

Copilot AI left a comment

Uh oh!

coderabbitai Bot commented May 18, 2026 •

edited

Loading

Walkthrough

Changes

Estimated code review effort

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Uh oh!

Conversation

mha1 commented Jan 22, 2026 • edited by coderabbitai Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary by CodeRabbit

Uh oh!

gagarinlg left a comment

Choose a reason for hiding this comment

Uh oh!

gagarinlg May 18, 2026

Choose a reason for hiding this comment

Uh oh!

mha1 May 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

coderabbitai Bot commented May 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Walkthrough

Changes

Estimated code review effort

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

mha1 commented Jan 22, 2026 •

edited by coderabbitai Bot

Loading

mha1 May 18, 2026 •

edited

Loading

coderabbitai Bot commented May 18, 2026 •

edited

Loading