FlexControl: Add support for knob button (X4S) as a configurable action

[rsaue]

Request preparation

• I used an AI assistant to help structure this request
• I checked for existing issues covering the same feature

What would you like?

Feature Request

What would you like?

Add handling for the X4S serial command from the FlexControl device —
emitted when the main tuning knob is pressed (single click). This would
allow users to assign a radio action to the knob button press, just as
the three AUX buttons (X1S, X2S, X3S) already support configurable actions.

Background / protocol reference

The FlexControl sends plain ASCII commands terminated with ; over its
serial port. The knob-as-button identifier is documented in third-party
projects that implement the protocol (e.g. https://github.com/brianbruff/flctrl):

• U; / U02; — knob rotated clockwise (with pulse count)
• D; / D02; — knob rotated counter-clockwise
• X1S; / X2S; / X3S; — AUX button 1/2/3 single press
• X4S; — main knob single press (currently unhandled in AetherSDR)

The Python reference implementation handles X4S to cycle tuning step
size — demonstrating that the command is reliably sent by the hardware.

SmartSDR equivalent

SmartSDR for Windows allows the knob press to be assigned to radio
functions just like the AUX buttons (e.g. toggle RIT, swap VFOs,
change tuning step). AetherSDR currently handles rotation but not
the knob press.

Suggested implementation

In whatever source file handles the FlexControl serial command parsing
(likely something like FlexControlController.cpp or similar):

1. Parse X4S alongside the existing X1S, X2S, X3S button handlers
2. Expose it in the FlexControl settings UI as "Knob Button" with a
   configurable action dropdown (same options available to the AUX buttons)
3. A sensible default action would be "Cycle Tune Step" (matching the
   Python reference and SmartSDR behaviour)

Why this matters

The knob button is physically the most natural and frequently pressed
control on the FlexControl — it sits right under the thumb during
tuning. Leaving it unmapped means operators lose a prime control
surface. Virtually all other FlexControl integrations (SmartSDR,
FTDXRC, DDUtil) support it.

73 LB2EG Richard

[aethersdr-agent]

This looks similar to #373 — is this the same issue, or something different? If it is the same, we can track it there. — AetherClaude (automated agent for AetherSDR)

[aethersdr-agent]

Triage Analysis

Thanks for the detailed write-up, Richard — and for the protocol reference.

Relationship to #373

This is a partial duplicate of #373 (also filed by you). Issue #373 requested two things:

1. Slice-switching via FlexControl buttons — already implemented (NextSlice/PrevSlice actions exist in the action list)
2. Using the knob press (X4S) as an additional button — not yet implemented, which is exactly what this issue requests

I'd suggest we track the X4S work here in #1295 since it's more specific and better documented, and close the slice-switching part of #373 as done.

Root Cause

The X4S command is explicitly filtered out in FlexControlManager::processCommand() at src/core/FlexControlManager.cpp:106:

int button = cmd.at(1) - '0';
if (button < 1 || button > 3) return;   // ← X4S is rejected here

The guard discards any button outside the 1–3 range. Additionally, the settings UI (RadioSetupDialog.cpp:2912) only loops over 3 buttons, and the defaults table in MainWindow.cpp:1485–1488 only has 3 rows. So three places need updating.

Proposed Fix

src/core/FlexControlManager.cpp — extend the guard from button > 3 to button > 4:

if (button < 1 || button > 4) return;

src/core/FlexControlManager.h — add X4S to the protocol comment block and update the buttonPressed signal doc to say buttons 1–4.

src/gui/MainWindow.cpp (~line 1485) — add a 4th row to the defaults table and extend the bounds check:

static const char* defaults[4][3] = {
    {"StepUp",     "StepDown",     "None"},
    {"ToggleMox",  "ToggleTune",   "None"},
    {"ToggleMute", "ToggleLock",   "None"},
    {"StepUp",     "StepDown",     "None"},  // Knob button — default to step cycling
};
// ...
const char* def = (button >= 1 && button <= 4 && action >= 0 && action <= 2)
                  ? defaults[button-1][action] : "None";

src/gui/RadioSetupDialog.cpp (~line 2904–2912) — extend the UI from 3 to 4 buttons:

static const char* defaultActions[4][2] = {
    {"StepUp", "StepDown"},
    {"ToggleMox", "ToggleTune"},
    {"ToggleMute", "ToggleLock"},
    {"StepUp", "StepDown"},      // Knob button defaults
};
static const char* btnLabels[4] = {"Button 1:", "Button 2:", "Button 3:", "Knob Button:"};
// ...
for (int b = 0; b < 4; ++b) {

Also need to bump the auto-detect checkbox grid row from 4 to 5 (and subsequent rows) since the new button row takes a slot.

Default Action

The issue suggests "Cycle Tune Step" as the default, matching SmartSDR and the Python reference. We already have StepUp/StepDown actions which cycle the tuning step — using StepUp for tap and StepDown for double-tap seems like a natural fit and is consistent with Button 1's defaults.

Questions

1. Does the FlexControl hardware also send X4C (double-tap) and X4L (long-press) for the knob button, or only X4S (single tap)? The code already parses the action character generically, so if the hardware sends them they'll work automatically — but it affects whether we should show double-tap config in the UI for the knob button.

---

— AetherClaude (automated triage for AetherSDR)

[aethersdr-agent]

Claude here — fix applied in PR #1296: #1296

What was changed: Add FlexControl knob button (X4S) as configurable action (#1295)

Files touched:

• src/core/FlexControlManager.cpp
• src/core/FlexControlManager.h
• src/gui/MainWindow.cpp
• src/gui/RadioSetupDialog.cpp

— AetherClaude (automated agent for AetherSDR)

[ten9876]

Claude here — merged into main. The FlexControl knob button press (X4S) is now handled as a configurable action, just like the three AUX buttons. Default is StepUp (tap) / StepDown (double-tap). Configure it in Radio Setup → Serial → Knob Button. Will be in the next release.

73, Jeremy KK7GWY & Claude (AI dev partner)