From 16922c26433b9aec9e09f4cc60fe5d5dd09a691a Mon Sep 17 00:00:00 2001
From: Yuri D'Elia <wavexx@thregr.org>
Date: Sun, 15 Jan 2023 17:32:56 +0100
Subject: [PATCH] TM: Restore extruder autofan state when stopping/resuming

During thermal errors all fans are set to full speed.

When the print is resumed or stopped *and* the thermal error is gone,
also restore the autofan state.

Fixes #3893
---
 Firmware/fancheck.cpp | 10 ++++++++++
 Firmware/fancheck.h   |  1 +
 Firmware/ultralcd.cpp | 10 +++++++++-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/Firmware/fancheck.cpp b/Firmware/fancheck.cpp
index 12724582..ad14e3b4 100755
--- a/Firmware/fancheck.cpp
+++ b/Firmware/fancheck.cpp
@@ -294,3 +294,13 @@ void hotendFanSetFullSpeed()
 #endif //FAN_SOFT_PWM
     fanSpeed = 255;
 }
+
+void hotendDefaultAutoFanState()
+{
+#if (defined(EXTRUDER_0_AUTO_FAN_PIN) && EXTRUDER_0_AUTO_FAN_PIN > -1)
+#ifdef EXTRUDER_ALTFAN_DETECT
+    altfanStatus.altfanOverride = eeprom_read_byte((uint8_t*)EEPROM_ALTFAN_OVERRIDE);
+#endif
+    setExtruderAutoFanState(1);
+#endif
+}
diff --git a/Firmware/fancheck.h b/Firmware/fancheck.h
index 31214397..0e0f2743 100755
--- a/Firmware/fancheck.h
+++ b/Firmware/fancheck.h
@@ -33,3 +33,4 @@ void checkExtruderAutoFans();
 
 void checkFans();
 void hotendFanSetFullSpeed();
+void hotendDefaultAutoFanState();
diff --git a/Firmware/ultralcd.cpp b/Firmware/ultralcd.cpp
index de20edaf..67f9d4af 100755
--- a/Firmware/ultralcd.cpp
+++ b/Firmware/ultralcd.cpp
@@ -5435,7 +5435,12 @@ void lcd_resume_print()
     st_synchronize();
     custom_message_type = CustomMsg::Resuming;
     isPrintPaused = false;
-    Stopped = false; // resume processing USB commands again
+
+    // resume processing USB commands again and restore hotend fan state (in case the print was
+    // stopped due to a thermal error)
+    hotendDefaultAutoFanState();
+    Stopped = false;
+
     restore_print_from_ram_and_continue(default_retraction);
     pause_time += (_millis() - start_pause_print); //accumulate time when print is paused for correct statistics calculation
     refresh_cmd_timeout();
@@ -6073,6 +6078,9 @@ void lcd_print_stop_finish()
     } else {
         // Turn off the print fan
         fanSpeed = 0;
+
+        // restore the auto hotend state
+        hotendDefaultAutoFanState();
     }
 
     if (mmu_enabled) extr_unload(); //M702 C