diff --git a/lambda-test/Makefile b/lambda-test/Makefile
index a981d1c..061a775 100644
--- a/lambda-test/Makefile
+++ b/lambda-test/Makefile
@@ -14,8 +14,8 @@
 
 ## If you've split your program into multiple .c / .h files, 
 ## include the additional source (in same directory) here 
-LOCAL_SOURCE = avrjunit.c adc-test.c alert-test.c command-test.c \
-display-test.c integers-test.c interrupts-test.c release-test.c \
+LOCAL_SOURCE = avrjunit.c utils.c adc-test.c airgate-test.c alert-test.c \
+command-test.c display-test.c integers-test.c interrupts-test.c release-test.c \
 rules-test.c scheduler-test.c sensors-test.c strings-test.c usart-test.c
 
 ## Here you can link to one more directory (and multiple .c files)
diff --git a/lambda-test/adc-test.c b/lambda-test/adc-test.c
index 140085c..36133a8 100644
--- a/lambda-test/adc-test.c
+++ b/lambda-test/adc-test.c
@@ -9,7 +9,6 @@
  */
 
 #include "avrjunit.h"
-#include "integers.h"
 #include "interrupts.h"
 #include "adc.h"
 #include "pins.h"
diff --git a/lambda-test/airgate-test.c b/lambda-test/airgate-test.c
new file mode 100644
index 0000000..fafe36a
--- /dev/null
+++ b/lambda-test/airgate-test.c
@@ -0,0 +1,129 @@
+/*
+ * airgate-test.c
+ *
+ *  Created on: 28.03.2016
+ *      Author: dode@luniks.net
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include "avrjunit.h"
+#include "pins.h"
+#include "airgate.h"
+#include "integers.h"
+#include "utils.h"
+
+/* Module airgate */
+
+static bool testSetAirgate(void) {
+
+	resetAirgate(0);
+	setAirgate(100);
+
+	assertTrue(isAirgateBusy());
+	// full motor current is set
+	assertTrue(bit_is_clear(PORT, PIN_CURRENT));
+	// direction 0
+	assertTrue(bit_is_clear(PORT, PIN_DIR));
+	// min speed is set
+	assertTrue(MIN_SPEED == OCR2A);
+	// timer2 is running (prescaler is set)
+	assertTrue(0 != TCCR2B);
+
+	stepUntilDone();
+
+	assertFalse(isAirgateBusy());
+	// reduced motor current is set
+	assertFalse(bit_is_clear(PORT, PIN_CURRENT));
+	// timer2 is stopped
+	assertTrue(0 == TCCR2B);
+	// requested position reached
+	assertTrue(100 == getAirgate());
+
+	return true;
+}
+
+static bool testMakeSteps(void) {
+
+	const uint16_t SPEED_PROD = (uint16_t)MIN_SPEED * MAX_SPEED;
+	const uint16_t ramp = MIN(abs(MAX_SPEED - MIN_SPEED), (100 << STEPPING_MODE) >> 1);
+	uint8_t speed = MIN_SPEED;
+
+	resetAirgate(0);
+	setAirgate(100);
+
+	// full motor current is set
+	assertTrue(bit_is_clear(PORT, PIN_CURRENT));
+	// step pin is low
+	assertTrue(bit_is_clear(PORT, PIN_STEP));
+	assertTrue(MIN_SPEED == OCR2A);
+
+	makeSteps();
+
+	// step pin is toggled high
+	assertTrue(bit_is_set(PORT, PIN_STEP));
+	// accelerated by 1
+	assertTrue((SPEED_PROD / ++speed) == OCR2A);
+
+	makeSteps();
+
+	// step pin is toggled low
+	assertTrue(bit_is_clear(PORT, PIN_STEP));
+	// no acceleration
+	assertTrue((SPEED_PROD / speed) == OCR2A);
+
+	// step until end of acceleration ramp
+	for (uint16_t i = 1; i < ramp; i++) {
+		makeSteps();
+		makeSteps();
+	}
+
+	// should have accelerated to MAX_SPEED
+	speed = MAX_SPEED;
+	assertTrue((SPEED_PROD / speed) == OCR2A);
+
+	// make remaining steps
+	stepUntilDone();
+
+	// step pin is toggled low
+	assertTrue(bit_is_clear(PORT, PIN_STEP));
+	// decelerated to MIN_SPEED
+	speed = MIN_SPEED;
+	assertTrue((SPEED_PROD / speed) == OCR2A);
+	// reached requested position
+	assertTrue(100 == getAirgate());
+	// reduced motor current is set
+	assertTrue(bit_is_set(PORT, PIN_CURRENT));
+
+	return true;
+}
+
+static bool testSetSleepMode(void) {
+
+	setSleepMode(false);
+
+	assertTrue(bit_is_set(PORT, PIN_SLEEP));
+
+	setSleepMode(true);
+
+	assertTrue(bit_is_clear(PORT, PIN_SLEEP));
+
+	return true;
+}
+
+/* Test "class" */
+static const char class[] PROGMEM = "airgate";
+
+/* Test names */
+static const char testSetAirgate_P[] PROGMEM = "testSetAirgate";
+static const char testMakeSteps_P[] PROGMEM = "testMakeSteps";
+static const char testSetSleepMode_P[] PROGMEM = "testSetSleepMode";
+
+/* Tests */
+static TestCase const tests[] = {
+		{class, testSetAirgate_P, testSetAirgate},
+		{class, testMakeSteps_P, testMakeSteps},
+		{class, testSetSleepMode_P, testSetSleepMode}
+};
+
+TestClass airgateClass = {tests, ARRAY_LENGTH(tests)};
diff --git a/lambda-test/alert-test.c b/lambda-test/alert-test.c
index 99bf76b..d2d9291 100644
--- a/lambda-test/alert-test.c
+++ b/lambda-test/alert-test.c
@@ -9,7 +9,6 @@
  */
 
 #include "avrjunit.h"
-#include "integers.h"
 #include "interrupts.h"
 #include "alert.h"
 
diff --git a/lambda-test/avrjunit.h b/lambda-test/avrjunit.h
index 1d0fef3..18206df 100644
--- a/lambda-test/avrjunit.h
+++ b/lambda-test/avrjunit.h
@@ -35,6 +35,11 @@
 #define assertNotNull(exp) if ((exp) == NULL) return false
 
 /**
+ * Computes the length of the given array.
+ */
+#define ARRAY_LENGTH(array) (sizeof(array) / sizeof(array[0]))
+
+/**
  * Function pointer for test functions taking no parameters and returning
  * true on success and false on failure.
  */
diff --git a/lambda-test/command-test.c b/lambda-test/command-test.c
index 26b550f..1de23c2 100644
--- a/lambda-test/command-test.c
+++ b/lambda-test/command-test.c
@@ -12,9 +12,10 @@
 #include "alert.h"
 #include "command.h"
 #include "display.h"
-#include "integers.h"
 #include "interrupts.h"
 #include "sensors.h"
+#include "airgate.h"
+#include "utils.h"
 
 /* Module command */
 
@@ -70,6 +71,18 @@
 	return true;
 }
 
+static bool testSetAirgate(void) {
+
+	resetAirgate(0);
+
+	runCommand("sa 100");
+	stepUntilDone();
+
+	assertTrue(100 == getAirgate());
+
+	return true;
+}
+
 /* Test "class" */
 static const char class[] PROGMEM = "command";
 
@@ -78,13 +91,15 @@
 static const char testIsLogging_P[] PROGMEM = "testIsLogging";
 static const char testHeater_P[] PROGMEM = "testHeater";
 static const char testCycleDisplay_P[] PROGMEM = "testCycleDisplay";
+static const char testSetAirgate_P[] PROGMEM = "testSetAirgate";
 
 /* Tests */
 static TestCase const tests[] = {
 		{class, testIsSimulation_P, testIsSimulation},
 		{class, testIsLogging_P, testIsLogging},
 		{class, testHeater_P, testHeater},
-		{class, testCycleDisplay_P, testCycleDisplay}
+		{class, testCycleDisplay_P, testCycleDisplay},
+		{class, testSetAirgate_P, testSetAirgate}
 };
 
 TestClass commandClass = {tests, ARRAY_LENGTH(tests)};
diff --git a/lambda-test/display-test.c b/lambda-test/display-test.c
index 6057024..4d4b8e8 100644
--- a/lambda-test/display-test.c
+++ b/lambda-test/display-test.c
@@ -11,7 +11,6 @@
 #include <string.h>
 #include "avrjunit.h"
 #include "display.h"
-#include "integers.h"
 #include "sensors.h"
 #include "alert.h"
 
diff --git a/lambda-test/interrupts-test.c b/lambda-test/interrupts-test.c
index e71db71..0202471 100644
--- a/lambda-test/interrupts-test.c
+++ b/lambda-test/interrupts-test.c
@@ -11,7 +11,6 @@
 #include <string.h>
 #include <util/delay.h>
 #include "avrjunit.h"
-#include "integers.h"
 #include "interrupts.h"
 
 /* Module interrupts */
diff --git a/lambda-test/lambda-test.c b/lambda-test/lambda-test.c
index 57f7dd0..a11d66f 100644
--- a/lambda-test/lambda-test.c
+++ b/lambda-test/lambda-test.c
@@ -25,6 +25,7 @@
 
 	extern TestClass releaseClass;
 	extern TestClass adcClass;
+	extern TestClass airgateClass;
 	extern TestClass alertClass;
 	extern TestClass commandClass;
 	extern TestClass displayClass;
@@ -41,6 +42,7 @@
 	// run these before interrupts are initialized to avoid interference
 	runClass(rulesClass);
 	runClass(adcClass);
+	runClass(airgateClass);
 	runClass(alertClass);
 	runClass(commandClass);
 	runClass(displayClass);
diff --git a/lambda-test/release-test.c b/lambda-test/release-test.c
index e481238..b53600e 100644
--- a/lambda-test/release-test.c
+++ b/lambda-test/release-test.c
@@ -9,7 +9,6 @@
  */
 
 #include "avrjunit.h"
-#include "integers.h"
 #include "interrupts.h"
 #include "messages.h"
 #include "pins.h"
diff --git a/lambda-test/rules-test.c b/lambda-test/rules-test.c
index 33dcfc4..fab9aa8 100644
--- a/lambda-test/rules-test.c
+++ b/lambda-test/rules-test.c
@@ -12,9 +12,9 @@
 #include "avrjunit.h"
 #include "rules.h"
 #include "alert.h"
-#include "integers.h"
 #include "interrupts.h"
 #include "airgate.h"
+#include "utils.h"
 
 /* Module rules */
 
@@ -22,13 +22,6 @@
 extern int8_t state;
 extern Rule rules[];
 
-static void stepUntilDone(void) {
-	while (isAirgateBusy()) {
-		makeSteps();
-	}
-	makeSteps();
-}
-
 static bool testAirgate50(void) {
 
 	Measurement meas = {0, 0, 0, 0};
@@ -455,7 +448,7 @@
 	return true;
 }
 
-static bool testHeaterTimeout0(void) {
+static bool testHeaterTimeout(void) {
 
 	resetRules(true);
 	resetTime();
@@ -477,28 +470,6 @@
 	return true;
 }
 
-static bool testHeaterTimeout1(void) {
-
-	resetRules(true);
-	resetTime();
-	Measurement meas = {0, 0, 0, 0};
-
-	setHeaterState(heaterStateOn);
-
-	// equal or more than 3 hours below TEMP_AIRGATE_0
-	addTime(10800UL);
-
-	meas.tempI = TEMP_AIRGATE_0 - 1;
-	meas.lambda = LAMBDA_MAX;
-	meas.current = milliAmpsReady;
-	reason(meas);
-	assertTrue(heaterStateOff == getHeaterState());
-
-	cancelAlert();
-
-	return true;
-}
-
 /* Test "class" */
 static const char class[] PROGMEM = "rules";
 
@@ -514,8 +485,7 @@
 static const char testHeaterFaultNoconn_P[] PROGMEM = "testHeaterFaultNoconn";
 static const char testHeaterFaultShort_P[] PROGMEM = "testHeaterFaultShort";
 static const char testHeaterFaultNoheat_P[] PROGMEM = "testHeaterFaultNoheat";
-static const char testHeaterTimeout0_P[] PROGMEM = "testHeaterTimeout0";
-static const char testHeaterTimeout1_P[] PROGMEM = "testHeaterTimeout1";
+static const char testHeaterTimeout_P[] PROGMEM = "testHeaterTimeout";
 
 /* Tests */
 static TestCase const tests[] = {
@@ -530,8 +500,7 @@
 		{class, testHeaterFaultNoconn_P, testHeaterFaultNoconn},
 		{class, testHeaterFaultShort_P, testHeaterFaultShort},
 		{class, testHeaterFaultNoheat_P, testHeaterFaultNoheat},
-		{class, testHeaterTimeout0_P, testHeaterTimeout0},
-		{class, testHeaterTimeout1_P, testHeaterTimeout1}
+		{class, testHeaterTimeout_P, testHeaterTimeout}
 };
 
 TestClass rulesClass = {tests, ARRAY_LENGTH(tests)};
diff --git a/lambda-test/scheduler-test.c b/lambda-test/scheduler-test.c
index 06ef9b2..bfe7b0b 100644
--- a/lambda-test/scheduler-test.c
+++ b/lambda-test/scheduler-test.c
@@ -6,7 +6,6 @@
  */
 
 #include "avrjunit.h"
-#include "integers.h"
 #include "interrupts.h"
 #include "scheduler.h"
 
diff --git a/lambda-test/sensors-test.c b/lambda-test/sensors-test.c
index f690e14..7d1f0e3 100644
--- a/lambda-test/sensors-test.c
+++ b/lambda-test/sensors-test.c
@@ -11,7 +11,6 @@
 #include <stdio.h>
 #include <string.h>
 #include "avrjunit.h"
-#include "integers.h"
 #include "interrupts.h"
 #include "adc.h"
 #include "sensors.h"
diff --git a/lambda-test/strings-test.c b/lambda-test/strings-test.c
index 0a9b727..83229ac 100644
--- a/lambda-test/strings-test.c
+++ b/lambda-test/strings-test.c
@@ -10,7 +10,6 @@
 
 #include <string.h>
 #include "avrjunit.h"
-#include "integers.h"
 #include "strings.h"
 
 /* Module strings */
diff --git a/lambda-test/usart-test.c b/lambda-test/usart-test.c
index 98f3611..63c074f 100644
--- a/lambda-test/usart-test.c
+++ b/lambda-test/usart-test.c
@@ -11,7 +11,6 @@
 #include "usart.h"
 #include <util/setbaud.h>
 #include "avrjunit.h"
-#include "integers.h"
 
 /* Module usart */
 
diff --git a/lambda-test/utils.c b/lambda-test/utils.c
new file mode 100644
index 0000000..fab2de0
--- /dev/null
+++ b/lambda-test/utils.c
@@ -0,0 +1,16 @@
+/*
+ * utils.c
+ *
+ *  Created on: 28.03.2016
+ *      Author: dode@luniks.net
+ */
+
+#include "utils.h"
+#include "airgate.h"
+
+void stepUntilDone(void) {
+	while (isAirgateBusy()) {
+		makeSteps();
+	}
+	makeSteps();
+}
diff --git a/lambda-test/utils.h b/lambda-test/utils.h
new file mode 100644
index 0000000..31d2e22
--- /dev/null
+++ b/lambda-test/utils.h
@@ -0,0 +1,19 @@
+/*
+ * utils.h
+ *
+ *  Created on: 28.03.2016
+ *      Author: dode@luniks.net
+ *
+ * Some utility functions used by many tests.
+ */
+
+#ifndef UTILS_H_
+#define UTILS_H_
+
+/**
+ * Trigger steps as done by the timer ISR until the requested motor position
+ * is reached.
+ */
+void stepUntilDone(void);
+
+#endif /* UTILS_H_ */
diff --git a/lambda/TODO b/lambda/TODO
index c615f43..712fa87 100644
--- a/lambda/TODO
+++ b/lambda/TODO
@@ -3,6 +3,7 @@
 * AVR
 
 * Functionality
+- Evaluate driver fault pin value (rule)
   
 * Circuit
 - AVCC should be connected to VCC via an LC network
diff --git a/lambda/airgate.c b/lambda/airgate.c
index 9ee2957..c84b745 100644
--- a/lambda/airgate.c
+++ b/lambda/airgate.c
@@ -6,11 +6,10 @@
  *
  *  Simple stepper motor control with a linear acceleration profile using the
  *  DRV8825. An absolute position from 0 to 255 can be set where 200 units
- *  correspond to 360° rotation.
+ *  correspond to 360° rotation (with 1.8 ° step angle).
  */
 
 #include <stdlib.h>
-#include <stdbool.h>
 #include <util/atomic.h>
 #include <util/delay.h>
 #include "airgate.h"
@@ -18,6 +17,8 @@
 #include "interrupts.h"
 #include "pins.h"
 
+static const uint16_t SPEED_PROD = (uint16_t)MIN_SPEED * MAX_SPEED;
+
 /* Direction */
 static volatile int8_t dir = 0;
 /* Current position */
@@ -49,6 +50,7 @@
 	// setup time
 	_delay_us(3);
 	// set start speed
+	speed = MIN_SPEED;
 	OCR2A = MIN_SPEED;
 	// start timer2
 	TCCR2B |= TIMER2_PRESCALE;
@@ -66,18 +68,21 @@
 void makeSteps(void) {
 	if (steps > 0) {
 		PORT ^= (1 << PIN_STEP);
-		done++;
-		steps--;
-		if (done < ramp && speed < MAX_SPEED) {
-			// accelerate within ramp
-			speed++;
-		} else if (steps < ramp && speed > MIN_SPEED) {
-			// decelerate within ramp
-			speed--;
+		if (bit_is_set(PORT, PIN_STEP)) {
+			done++;
+			steps--;
+			if (done < ramp && speed < MAX_SPEED) {
+				// accelerate within ramp
+				speed++;
+			} else if (steps < ramp && speed > MIN_SPEED) {
+				// decelerate within ramp
+				speed--;
+			}
+			// linearize an unfavourably increasing acceleration curve
+			OCR2A = SPEED_PROD / speed;
 		}
-		// linearize an unfavourably increasing acceleration curve
-		OCR2A = ((uint16_t)MIN_SPEED * MAX_SPEED) / speed;
 	} else {
+		PORT &= ~(1 << PIN_STEP);
 		stop();
 		pos += (done * dir);
 		done = 0;
@@ -93,7 +98,7 @@
 	if (bit_is_clear(PORT, PIN_SLEEP)) {
 		setSleepMode(false);
 	}
-	int16_t diff = (((int16_t)target) << SCALE) - pos;
+	int16_t diff = (((int16_t)target) << STEPPING_MODE) - pos;
 	if (diff != 0) {
 		dir = (diff > 0) - (diff < 0);
 		steps = abs(diff);
@@ -103,15 +108,7 @@
 }
 
 uint8_t getAirgate(void) {
-	return pos >> SCALE;
-}
-
-uint8_t getAirgateInPercent(void) {
-	if (getAirgate() == 0) {
-		return 0;
-	}
-
-	return 100000 / ((AIRGATE_OPEN * 1000UL) / getAirgate());
+	return pos >> STEPPING_MODE;
 }
 
 bool isAirgateBusy(void) {
@@ -135,7 +132,7 @@
 
 void resetAirgate(uint16_t const position) {
 	dir = 0;
-	pos = position << SCALE;
+	pos = position << STEPPING_MODE;
 	steps = 0;
 	done = 0;
 	ramp = 0;
diff --git a/lambda/airgate.h b/lambda/airgate.h
index 0dfa80b..bc6693c 100644
--- a/lambda/airgate.h
+++ b/lambda/airgate.h
@@ -5,6 +5,9 @@
  *      Author: dode@luniks.net
  */
 
+#include <stdint.h>
+#include <stdbool.h>
+
 #ifndef AIRGATE_H_
 #define AIRGATE_H_
 
@@ -19,10 +22,9 @@
 #define AIRGATE_OPEN 	60
 
 /**
- * 1 = full step, 2 = half step, 3 = 1/4 step, 4 = 8 microsteps, ...
- * for 180°.
+ * 0 = full step, 1 = half step, 2 = 1/4 step, 3 = 8 microsteps, ...
  */
-#define SCALE 3
+#define STEPPING_MODE 2
 
 /**
  * Called from the timer interrupt ISR and makes a half step or stops the
@@ -32,7 +34,7 @@
 
 /**
  * Sets the airgate position 0 - 255, where 200 units correspond to 360°
- * rotation.
+ * rotation (with 1.8 ° step angle).
  */
 void setAirgate(uint8_t const position);
 
@@ -43,11 +45,6 @@
 uint8_t getAirgate(void);
 
 /**
- * Returns the current airgate position translated to percent.
- */
-uint8_t getAirgateInPercent(void);
-
-/**
  * Returns true if the motor is currently busy setting an airgate position,
  * false otherwise.
  */
diff --git a/lambda/display.c b/lambda/display.c
index 44eb9df..dae8e04 100644
--- a/lambda/display.c
+++ b/lambda/display.c
@@ -83,8 +83,12 @@
  * Displays the airgate position in %.
  */
 static void displayAirgate(uint8_t const airgate) {
+	uint16_t airgateInPercent = 0;
+	if (airgate > 0) {
+		airgateInPercent = 100000UL / ((AIRGATE_OPEN * 1000UL) / airgate);
+	}
 	char line1[17];
-	snprintf(line1, sizeof(line1), "%d%%", airgate);
+	snprintf(line1, sizeof(line1), "%d%%", airgateInPercent);
 	setText(MSG_AIRGATE, line1);
 }
 
@@ -137,7 +141,7 @@
 		if (position == displayPosMax) {
 			displayMeas(measMax, " ^");
 		} else if (position == displayPosAirgate) {
-			displayAirgate(getAirgateInPercent());
+			displayAirgate(getAirgate());
 		} else if (position == displayPosHeater) {
 			displayCurrent(measLatest.current);
 		} else if (position == displayPosLastText) {