Avoid homing the idler at start when printing

src/main.cpp

@@ -113,8 +113,8 @@ void setup() {
     }
     ml::leds.Step();
 
-    // Idler will home on its own by default
+    // Idler and Selector decide whether homing is possible/safe
-    // Selector decides whether homing is possible
+    mi::idler.Init();
     ms::selector.Init();
 }
 

src/modules/idler.cpp

@@ -1,6 +1,7 @@
 /// @file idler.cpp
 #include "idler.h"
 #include "buttons.h"
+#include "globals.h"
 #include "leds.h"
 #include "motion.h"
 #include "permanent_storage.h"
@@ -76,7 +77,10 @@ Idler::OperationResult Idler::Engage(uint8_t slot) {
     }
 
     // coordinates invalid, first home, then engage
-    if (!homingValid) {
+    // avoid homing if filament in fsensor or in nozzle
+    // - the printer may be printing right now and holding the filament
+    // against the pulley even for a short period of time may not be healthy
+    if (!homingValid && mg::globals.FilamentLoaded() < mg::InFSensor) {
         PlanHome(mm::Idler);
         return OperationResult::Accepted;
     }
@@ -102,7 +106,7 @@ bool Idler::Step() {
         PerformHome(mm::Idler);
         return false;
     case Ready:
-        if (!homingValid) {
+        if (!homingValid && mg::globals.FilamentLoaded() < mg::InFSensor) {
             PlanHome(mm::Idler);
             return false;
         }
@@ -114,5 +118,16 @@ bool Idler::Step() {
     }
 }
 
+void Idler::Init() {
+    if (mg::globals.FilamentLoaded() < mg::InFSensor) {
+        // home the Idler only in case we don't have filament loaded in the printer (or at least we think we don't)
+        PlanHome(mm::Idler);
+    } else {
+        // otherwise set selector's position according to know slot positions (and pretend it is correct)
+        mm::motion.SetPosition(mm::Idler, SlotPosition(mg::globals.ActiveSlot()).v);
+        InvalidateHoming(); // and plan homing sequence ASAP
+    }
+}
+
 } // namespace idler
 } // namespace modules

src/modules/idler.h

@@ -45,6 +45,12 @@ public:
     /// @returns the index of idle position of the idler, usually 5 in case of 0-4 valid indices of filament slots
     inline static constexpr uint8_t IdleSlotIndex() { return config::toolCount; }
 
+    /// Initializes the idler after restart/cold boot
+    /// Reads the active slot from the EEPROM and decides if the idler is safe to move (not hold the filament while printing)
+    /// - free -> home the idler
+    /// - blocked -> set idler's position according to the active filament slot
+    void Init();
+
 protected:
     virtual void PrepareMoveToPlannedSlot() override;
     virtual void PlanHomingMove() override;