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Avoid nozzle heat loss when restarting after a cancelled print #585

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d195107
Update README.md
leomeyer Aug 12, 2025
47dc7c9
Add M104 parameter C<min_temp>: Sets the target temperature to the cu…
leomeyer Aug 12, 2025
cc80044
Revert "Update README.md"
leomeyer Aug 12, 2025
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24 changes: 20 additions & 4 deletions Marlin/src/gcode/temp/M104_M109.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -50,9 +50,11 @@
* M109: Set Hotend Temperature target and wait
*
* Parameters
* I<preset> : Material Preset index (if material presets are defined)
* T<index> : Tool index. If omitted, applies to the active tool
* S<target> : The target temperature in current units. For M109, only wait when heating up.
* I<preset> : Material Preset index (if material presets are defined)
* T<index> : Tool index. If omitted, applies to the active tool
* C<min_temp> : Sets the target temperature to the current temperature of the selected tool
* or to min_temp if it is higher. This can avoid unnecessary heat loss.
* S<target> : The target temperature in current units. For M109, only wait when heating up.
*
* With AUTOTEMP...
* F<factor> : Autotemp Scaling Factor. Set non-zero to enable Auto-temp.
Expand All @@ -65,6 +67,7 @@
* Examples
* M104 S100 : Set target to 100° and return.
* M109 R150 : Set target to 150°. Wait until the hotend gets close to 150°.
* M104 C100 : Set target to 100° or the current temperature, whichever is higher.
*
* With PRINTJOB_TIMER_AUTOSTART turning on heaters will start the print job timer
* (used by printingIsActive, etc.) and turning off heaters will stop the timer.
Expand Down Expand Up @@ -92,8 +95,21 @@ void GcodeSuite::M104_M109(const bool isM109) {
}
#endif

// Get the temperature from 'S' or 'R'
bool no_wait_for_cooling = false;

// Avoid nozzle heat loss:
// If 'C' is specified for M104 keep the hotend at its current temperature.
// The value after 'C' specifies the minimum temperature (to avoid heating to e. g. 20 °C).
if (!got_temp && !isM109 && parser.seenval('C')) {
celsius_t min_temp = parser.value_celsius();
temp = thermalManager.wholeDegHotend(target_extruder);
// If the current temperature is below the minimum, start heating to the minimum
if (temp < min_temp)
temp = min_temp;
no_wait_for_cooling = got_temp = true;
}

// Get the temperature from 'S' or 'R'
if (!got_temp) {
no_wait_for_cooling = parser.seenval('S');
got_temp = no_wait_for_cooling || (isM109 && parser.seenval('R'));
Expand Down