fix(icom): verify the data flag after a mode set, and correct it with 0x26

The IC-7760 acknowledges the 1A 06 data-mode command and stays in USB-D
anyway, which left the operator unable to get back to plain USB from the
console at all. After every mode set the flag is read back; on a mismatch it
is said again with 0x26 — mode, data flag and filter in one frame, the form
the newer rigs actually honour. Only on a mismatch, so rigs that predate 0x26
never see the command.

changelog.json

@@ -7,14 +7,16 @@
       "Elecraft console: an SWR spike (the K3’s own blip at the end of an FT8 frame) no longer fades over twelve seconds — the peak shows briefly, then the meter returns straight to the live reading.",
       "Icom: the IC-7760 joins the model list (CI-V address B2h).",
       "Icom console: the IC-7760 gets its real attenuator steps — 6/12/18 dB.",
-      "Icom network audio: the RX stream is decoded correctly — mono is requested and the payload offset was confirmed on a real IC-7760, curing the garbled, clicking audio."
+      "Icom network audio: the RX stream is decoded correctly — mono is requested and the payload offset was confirmed on a real IC-7760, curing the garbled, clicking audio.",
+      "Icom: switching back from a data mode (USB-D1) to plain USB now sticks — if the rig ignores the data-flag command, it is repeated with the modern one-frame form (0x26). Seen on the IC-7760."
     ],
     "fr": [
       "Console Elecraft : le S-mètre est calibré sur un vrai K3 — S9 et les +dB correspondent désormais à l’affichage de la radio (il lisait environ deux points S trop bas).",
       "Console Elecraft : un pic de ROS (le sursaut du K3 en fin de trame FT8) ne s’estompe plus pendant douze secondes — le pic s’affiche brièvement, puis le ros-mètre revient directement à la valeur réelle.",
       "Icom : l’IC-7760 rejoint la liste des modèles (adresse CI-V B2h).",
       "Console Icom : l’IC-7760 reçoit ses vrais crans d’atténuateur — 6/12/18 dB.",
-      "Audio réseau Icom : le flux RX est décodé correctement — le mono est demandé et l’offset du payload a été confirmé sur un vrai IC-7760, ce qui guérit le son inaudible et les clics."
+      "Audio réseau Icom : le flux RX est décodé correctement — le mono est demandé et l’offset du payload a été confirmé sur un vrai IC-7760, ce qui guérit le son inaudible et les clics.",
+      "Icom : revenir d’un mode data (USB-D1) au USB simple tient désormais — si la radio ignore la commande du drapeau data, elle est répétée sous la forme moderne en une trame (0x26). Constaté sur l’IC-7760."
     ]
   },
   {

internal/cat/civ/civ.go

@@ -36,6 +36,7 @@ const (
 	CmdVfoFreq        = 0x25 // read a specific VFO's freq (sub 0x00 selected, 0x01 unselected)
 	CmdPTT            = 0x1C // sub 0x00 = PTT
 	CmdExtra          = 0x1A // sub 0x06 = data mode on modern Icoms
+	CmdModeDataFil    = 0x26 // sub 0x00 = selected VFO: mode + data flag + filter in one frame
 	CmdReadID         = 0x19 // sub 0x00 = rig's own CI-V address (identifies model)
 	CmdPower          = 0x18 // power on/off (sub 0x01 = on, 0x00 = off; on needs an FE wake preamble)
 

internal/cat/icomserial.go

@@ -559,6 +559,18 @@ func (b *IcomSerial) SetMode(mode string) error {
 	}
 	// Filter 0x01 (FIL1) is the conventional default for the data-mode set.
 	_ = b.execIdempotent("set data mode", civ.CmdExtra, civ.SubDataMode, dataByte, 0x01)
+	// Trust, then verify: the IC-7760 acknowledges 1A 06 and stays in USB-D
+	// anyway, which left an operator unable to get back to plain USB at all.
+	// When the readback disagrees, say it again with 0x26 — mode, data flag and
+	// filter in one frame, the command the newer rigs actually honour. Only on
+	// a mismatch, so rigs that predate 0x26 never see it.
+	if got := b.readDataMode(); got != data {
+		if err := b.execIdempotent("set mode+data (0x26)", civ.CmdModeDataFil, 0x00, code, dataByte, 0x01); err != nil {
+			applog.Printf("icom: data flag stuck at %v after mode %s, and 0x26 failed too: %v", got, mode, err)
+		} else {
+			applog.Printf("icom: data flag stuck after 1A06, corrected via 0x26 (mode %s)", mode)
+		}
+	}
 	return nil
 }