diff --git a/lambda/airgate.c b/lambda/airgate.c
index 7bb5a2d..ec1f9df 100644
--- a/lambda/airgate.c
+++ b/lambda/airgate.c
@@ -14,20 +14,27 @@
 
 #include "usart.h"
 
-#define MIN_SPEED 150
-#define MAX_SPEED 20
-// 1 = full step, 2 = half step, 3 = 1/4 step, 4 = 8 microsteps, ...
-#define SCALE 3
-
 // TODO pins
 
+/* Direction */
 static int8_t dir = 0;
+/* Current position */
 static uint16_t pos = 0;
+/* Target position */
+static int16_t target = 0;
+/* Steps remaining */
 static uint16_t steps = 0;
+/* Steps done */
 static uint16_t done = 0;
+/* Acceleration profile ramp */
 static uint16_t ramp = 0;
+/* Speed */
 static uint8_t speed = MIN_SPEED;
 
+/**
+ * Wakes up the driver if sleeping, sets the direction and initial speed and
+ * starts the motor by starting the timer.
+ */
 static void start(void) {
 	if (bit_is_clear(PORTC, PC5)) {
 		// wake up driver
@@ -49,41 +56,66 @@
 	TCCR2B |= (1 << CS22) | (1 << CS21);
 }
 
+/**
+ * Stops the motor by stopping the timer.
+ */
 static void stop(void) {
 	// stop timer2
 	TCCR2B = 0;
 	// GTCCR |= (1 << PSRASY);
 }
 
+/**
+ * Calculates the direction and steps to take to get to the target position,
+ * the ramp length for the acceleration profile, sets the speed and starts
+ * the motor.
+ */
+static void set(void) {
+	done = 0;
+	int16_t diff = (target << SCALE) - pos;
+	if (diff != 0) {
+		target = -1;
+		dir = MAX(-1, MIN(diff, 1));
+		steps = abs(diff);
+		ramp = MIN(MIN_SPEED - MAX_SPEED, steps >> 1);
+		speed = MIN_SPEED;
+		start();
+	}
+}
+
 void makeSteps(void) {
 	if (steps > 0) {
 		PORTB ^= (1 << PB7);
 		pos += dir;
 		steps--;
 		done++;
-		if (done < ramp && speed > MAX_SPEED) --speed;
-		if (steps < ramp && speed < MIN_SPEED) ++speed;
+		// accelerate within ramp
+		if (done < ramp && speed > MAX_SPEED) speed--;
+		// decelerate within ramp
+		if (steps < ramp && speed < MIN_SPEED) speed++;
 		OCR2A = speed;
 	} else {
-		stop();
 		done = 0;
-		if (pos == 0) {
+		stop();
+		if (target != -1) {
+			// move to target position
+			set();
+		} else if (pos == 0) {
 			// driver sleep mode
+			// TODO when is it best to do this?
 			PORTC &= ~(1 << PC5);
 		}
 	}
 }
 
 void setAirgate(uint8_t const position) {
-	stop();
-	done = 0;
-	int16_t diff = (((int16_t)position) << SCALE) - pos;
-	if (diff != 0) {
-		dir = MAX(-1, MIN(diff, 1));
-		steps = abs(diff);
-		speed = MIN_SPEED;
-		ramp = MIN(MIN_SPEED - MAX_SPEED, steps >> 1);
-		start();
+	target = position;
+	if (steps > 0) {
+		// motor busy - decelerate and move to target position when stopped
+		steps = MIN(ramp, steps);
+	} else {
+		// move to target position
+		set();
 	}
 }
 
diff --git a/lambda/airgate.h b/lambda/airgate.h
index 8757c34..6fbf49f 100644
--- a/lambda/airgate.h
+++ b/lambda/airgate.h
@@ -5,13 +5,35 @@
  *      Author: dode@luniks.net
  */
 
-#ifndef MOTOR_H_
-#define MOTOR_H_
+#ifndef AIRGATE_H_
+#define AIRGATE_H_
 
+#define MIN_SPEED 150
+#define MAX_SPEED 20
+/**
+ * 1 = full step, 2 = half step, 3 = 1/4 step, 4 = 8 microsteps, ...
+ * for 180°.
+ */
+#define SCALE 3
+
+/**
+ * Called from the timer interrupt ISR and makes one step or stops the
+ * timer/motor if the target position is reached.
+ */
 void makeSteps(void);
 
-uint8_t getAirgate(void);
-
+/**
+ * Sets the airgate position 0 - 100%. The actual number of degrees the motor
+ * spins depends on the SCALE and the stepping mode. If the motor is currently
+ * moving to a target position when this function is called, it is first
+ * decelerated and then moves to the new target position.
+ */
 void setAirgate(uint8_t const position);
 
-#endif /* MOTOR_H_ */
+/**
+ * Returns the current airgate position, assuming the motor did all the steps
+ * it was requested to do.
+ */
+uint8_t getAirgate(void);
+
+#endif /* AIRGATE_H_ */