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/******************************************************************************
* The MIT License
*
* Copyright (c) 2010, LeafLabs, LLC.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*****************************************************************************/
#ifndef _SERVO_H_
#define _SERVO_H_
#include <stdint.h>
#include "HardwareTimer.h"
/* Note on Arduino compatibility:
In the Arduino implementation, PWM is done "by hand" in the sense
that timer channels are hijacked in groups and an ISR is set which
toggles Servo::attach()ed pins using digitalWrite().
While this scheme allows any pin to drive a servo, it chews up
cycles and complicates the programmer's notion of when a particular
timer channel will be in use.
This implementation only allows Servo instances to Servo::attach()
to pins that already have a timer channel associated with them, and
just uses pwmWrite() to drive the wave.
This introduces an incompatibility: while the Arduino
implementation of attach() returns the affected channel on success
and 0 on failure, this one returns true on success and false on
failure.
RC Servos expect a pulse every 20ms. Since periods are set for
entire timers, rather than individual channels, attach()ing a Servo
to a pin can interfere with other pins associated with the same
timer. As always, the pin mapping mega table is your friend.
*/
// Pin number of unattached pins
#define NOT_ATTACHED (-1)
// Maximum angle in degrees you can write(), exclusive. Value chosen
// for Arduino compatibility.
#define SERVO_MAX_WRITE_ANGLE (200)
// Default min (0 deg)/max(180 deg) pulse widths, in microseconds.
// Value chosen for Arduino compatibility.
#define SERVO_DEFAULT_MIN_PW (544)
#define SERVO_DEFAULT_MAX_PW (2400)
class Servo {
public:
Servo();
/* Pin has to have a timer channel associated with it already;
* sets pinMode to PWM and returns true iff successful (failure
* when pin doesn't support PWM). doesn't detach any ISRs
* associated with timer channel. */
bool attach(uint8_t pin);
/* Like attach(int), but with (inclusive) min (0 degree) and max
* (180 degree) pulse widths, in microseconds.
*/
bool attach(uint8_t pin, uint16_t min, uint16_t max);
/* Return pin number if currently attach()ed to a pin,
NOT_ATTACHED otherwise. */
int attached() const { return pin; }
/* Stop driving the wave by disabling the output compare
interrupt. Returns true if this call did anything. */
bool detach();
/* If value < MAX_WRITE_ANGLE, treated as an angle in degrees.
Otherwise, it's treated as a pulse width. */
void write(unsigned int value);
/* If outside of [min, max] determined by attach(), it is clamped
to lie in that range. */
void writeMicroseconds(uint16_t pulseWidth);
/* Return servo target angle, in degrees. This will lie between 0
and 180. */
int read() const;
/* Returns the current pulse width, in microseconds. This will
lie within the [min, max] range. */
uint16_t readMicroseconds() const;
private:
int8_t pin;
HardwareTimer *timer;
int channel;
uint16_t min;
uint16_t max;
};
#endif /* _SERVO_H_ */
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