add NO_AUTO_IDLE option to prevent powercuts after inactivity, add temp_all_zero so power isn't cut if heater remains off for a while but has a non-zero set temperature

clock.c

@@ -23,17 +23,21 @@
 	called from clock_10ms(), do not call directly
 */
 void clock_250ms() {
-	if (steptimeout > (30 * 4)) {
+	#ifndef	NO_AUTO_IDLE
-		power_off();
+	if (temp_all_zero())	{
-	}
+		if (steptimeout > (30 * 4)) {
-	else if (heaters_all_off())	{
+			power_off();
-		uint8_t save_reg = SREG;
+		}
-		cli();
+		else {
-		CLI_SEI_BUG_MEMORY_BARRIER();
+			uint8_t save_reg = SREG;
-		steptimeout++;
+			cli();
-		MEMORY_BARRIER();
+			CLI_SEI_BUG_MEMORY_BARRIER();
-		SREG = save_reg;
+			steptimeout++;
+			MEMORY_BARRIER();
+			SREG = save_reg;
+		}
 	}
+	#endif
 
 	ifclock(clock_flag_1s) {
 		if (DEBUG_POSITION && (debug_flags & DEBUG_POSITION)) {

temp.c

@@ -326,6 +326,17 @@ uint16_t temp_get(temp_sensor_t index) {
 	return temp_sensors_runtime[index].last_read_temp;
 }
 
+uint8_t temp_all_zero() {
+	uint8_t i;
+	for (i = 0; i < NUM_TEMP_SENSORS; i++) {
+		if (temp_sensors[i].heater < NUM_HEATERS) {
+			if (temp_sensors_runtime[i].target_temp)
+				return 0;
+		}
+	}
+	return 255;
+}
+
 // extruder doesn't have sersendf_P
 #ifndef	EXTRUDER
 /// send temperatures to host

temp.h

@@ -41,6 +41,8 @@ uint8_t	temp_achieved(void);
 void temp_set(temp_sensor_t index, uint16_t temperature);
 uint16_t temp_get(temp_sensor_t index);
 
+uint8_t temp_all_zero(void);
+
 void temp_print(temp_sensor_t index);
 
 #endif	/* _TEMP_H */