drivers: added servo motor driver

drivers/Makefile

@@ -34,5 +34,8 @@ endif
 ifneq (,$(filter rgbled,$(USEMODULE)))
     DIRS += rgbled
 endif
+ifneq (,$(filter servo,$(USEMODULE)))
+    DIRS += servo
+endif
 
 include $(RIOTBASE)/Makefile.base

drivers/include/servo.h

+/*
+ * Copyright (C) 2014 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License v2.1. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/**
+ * @defgroup    driver_servo Servo Motor Driver
+ * @ingroup     drivers
+ * @brief       High-level driver for servo motors
+ * @{
+ *
+ * @file
+ * @brief       High-level driver for easy handling of servo motors
+ *
+ * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ */
+
+#ifndef __SERVO_H
+#define __SERVO_H
+
+#include "periph/pwm.h"
+
+
+/**
+ * @name Descriptor struct for a servo
+ */
+typedef struct {
+    pwm_t device;       /**< the PWM device driving the servo */
+    int channel;        /**< the channel the servo is connected to */
+    unsigned int min;   /**< minimum pulse width, in us */
+    unsigned int max;   /**< maximum pulse width, in us */
+} servo_t;
+
+/**
+ * @brief Initialize a servo motor by assigning it a PWM device and channel
+ *
+ * Digital servos are controlled by regular pulses sent to them. The width
+ * of a pulse determines the position of the servo. A pulse width of 1.5ms
+ * puts the servo in the center position, a pulse width of about 1.0ms and
+ * about 2.0ms put the servo to the maximum angles. These values can however
+ * differ slightly from servo to servo, so the min and max values are
+ * parameterized in the init function.
+ *
+ * The servo is initialized with fixed PWM values:
+ * - frequency: 100Hz (10ms interval)
+ * - resolution: 10000 (1000 steps per ms)
+ *
+ * Caution: When initializing a servo, the PWM device will be reconfigured to
+ * new frequency/resolution values. It is however fine to use multiple servos
+ * with the same PWM device, just on different channels.
+ *
+ * @param[out] dev          struct describing the servo
+ * @param[in] pwm           the PWM device the servo is connected to
+ * @param[in] pwm_channel   the PWM channel the servo is connected to
+ * @param[in] min           minimum pulse width in us
+ * @param[in] max           maximum pulse width in us
+ *
+ * @return                  0 on success
+ * @return                  <0 on error
+ */
+int servo_init(servo_t *dev, pwm_t pwm, int pwm_channel, unsigned int min, unsigned int max);
+
+/**
+ * @brief Set the servo motor to a specified position
+ *
+ * The position of the servo is specified in the pulse width that controls the
+ * servo. A value of 1500 means a pulse width of 1.5 ms, which is the center
+ * position on most servos.
+ *
+ * In case pos is larger/smaller then the max/min values, pos will be set to
+ * these values.
+ *
+ * @param[in] dev           the servo to set
+ * @param[in] pos           the position to set the servo in us
+ *
+ * @return                  0 on success
+ * @return                  -1 on invalid configured channel
+ * @return                  -2 on invalid position
+ */
+int servo_set(servo_t *dev, unsigned int pos);
+
+#endif /* __SERVO_H */
+/** @} */

drivers/servo/Makefile

+MODULE = servo
+
+include $(RIOTBASE)/Makefile.base

drivers/servo/servo.c

+/*
+ * Copyright (C) 2014 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License v2.1. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/**
+ * @ingroup     driver_servo
+ * @{
+ *
+ * @file
+ * @brief       Servo motor driver implementation
+ *
+ * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ *
+ * @}
+ */
+
+#include "servo.h"
+#include "periph/pwm.h"
+
+#define FREQUENCY       (100U)
+#define RESOLUTION      (10000U)
+
+int servo_init(servo_t *dev, pwm_t pwm, int pwm_channel, unsigned int min, unsigned int max)
+{
+    dev->device = pwm;
+    dev->channel = pwm_channel;
+    dev->min = min;
+    dev->max = max;
+
+    return pwm_init(dev->device, PWM_LEFT, FREQUENCY, RESOLUTION);
+}
+
+int servo_set(servo_t *dev, unsigned int pos)
+{
+    if (pos > dev->max) {
+        pos = dev->max;
+    }
+    else (pos < dev->min) {
+        pos = dev->min;
+    }
+    return pwm_set(dev->device, dev->channel, pos);
+}