[education/kstars] kstars/ekos/align: Fix align hang when a slew completes without an observable IPS_BUSY

Git commit 6b46891bf8018b758b9682938a98a2f0ce62748b by Jasem Mutlaq.
Committed on 15/08/2026 at 10:11.
Pushed by mutlaqja into branch 'master'.

Fix align hang when a slew completes without an observable IPS_BUSY

Some mount drivers finish very short corrective slews (e.g. the small
residual left after a Sync) within a single status tick and never emit
an intermediate IPS_BUSY for EQUATORIAL_EOD_COORD/COORD. Align's
ALIGN_SLEWING handler only trusted an IPS_OK once it had witnessed
IPS_BUSY (or a 10s timer elapsed), and that elapsed-timer fallback is
only re-evaluated when a new property update arrives - so once the
mount settled and stopped pushing updates, align was stuck forever,
never re-triggering capture/plate-solving.

Snapshot the mount's reported RA/DE right before Slew() commands the
move, and also accept an IPS_OK whose position differs from that
snapshot as proof of a genuine completion. IPS_OK means "not busy" by
INDI convention, so a changed position can only mean the mount already
reported completion, never that it's still mid-slew - this can't fire
while a slew, however long, is still genuinely in progress.

M  +5    -0    kstars/ekos/align/align.h
M  +23   -1    kstars/ekos/align/align_goto.cpp

https://invent.kde.org/education/kstars/-/commit/6b46891bf8018b758b9682938a98a2f0ce62748b

diff --git a/kstars/ekos/align/align.h b/kstars/ekos/align/align.h
index 258a032c30..353e1c55c1 100644
--- a/kstars/ekos/align/align.h
+++ b/kstars/ekos/align/align.h
@@ -915,6 +915,11 @@ class Align : public QWidget, public Ui::Align
         // Only wait this many milliseconds for slew to start.
         // Otherwise assume it has begun.
         static constexpr int MAX_WAIT_FOR_SLEW_START_MSEC = 10000;
+        // Mount's reported RA/DE (raw property values) right before the last Slew() was
+        // commanded. Lets the ALIGN_SLEWING/IPS_OK handler recognize a fresh completion even
+        // when no IPS_BUSY was ever observed for that slew.
+        double m_PreSlewRA { 0 };
+        double m_PreSlewDE { 0 };
 
         // Online and Offline parsers
         AstrometryParser* parser { nullptr };
diff --git a/kstars/ekos/align/align_goto.cpp b/kstars/ekos/align/align_goto.cpp
index 484120dfdb..a6c554d0ae 100644
--- a/kstars/ekos/align/align_goto.cpp
+++ b/kstars/ekos/align/align_goto.cpp
@@ -185,7 +185,17 @@ void Align::updateProperty(INDI::Property prop)
 
                     case ALIGN_SLEWING:
 
-                        if (!didSlewStart())
+                        // didSlewStart() only trusts an IPS_OK if we previously witnessed an
+                        // IPS_BUSY for this slew (or a 10s timer has elapsed). Some drivers
+                        // complete very short slews within a single status tick and never emit
+                        // an observable IPS_BUSY, so that condition alone can stay false forever
+                        // even though the mount genuinely already moved. Also accept the update
+                        // if the reported position differs from what it was right before this
+                        // slew was commanded: IPS_OK means "not busy" by INDI convention, so a
+                        // changed position can only mean the mount already reported completion,
+                        // never that it's still mid-slew.
+                        if (!didSlewStart() &&
+                                nvp->np[0].value == m_PreSlewRA && nvp->np[1].value == m_PreSlewDE)
                         {
                             qCDebug(KSTARS_EKOS_ALIGN) << "Mount slew planned, but not started slewing yet...";
                             break;
@@ -484,6 +494,18 @@ void Align::Slew()
     setState(ALIGN_SLEWING);
     Q_EMIT newStatus(state);
 
+    // Snapshot the mount's currently-reported coordinates before commanding the slew, so the
+    // ALIGN_SLEWING/IPS_OK handler above can tell a fresh completion from a stale, pre-slew
+    // property value that simply hasn't been superseded by an observable IPS_BUSY yet.
+    if (auto pn = m_Mount->getNumber(m_Mount->isJ2000() ? "EQUATORIAL_COORD" : "EQUATORIAL_EOD_COORD"))
+    {
+        if (auto nvp = pn.getNumber())
+        {
+            m_PreSlewRA = nvp->np[0].value;
+            m_PreSlewDE = nvp->np[1].value;
+        }
+    }
+
     if (m_Mount->Slew(&m_TargetCoord))
     {
         slewStartTimer.start();