Timer0 and Servo library support

This exposes the Timer0
This provides a Servo library support compatible with Arduino Servo
library but only supports the two timers the esp8266 has available

libraries/Servo/src/Servo.h

@@ -0,0 +1,93 @@
+/*
+  Servo.h - Interrupt driven Servo library for Esp8266 using timers
+  Copyright (c) 2015 Michael C. Miller. All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+  */
+
+
+//   A servo is activated by creating an instance of the Servo class passing
+//   the desired pin to the attach() method.
+//   The servos are pulsed in the background using the value most recently
+//   written using the write() method.
+//
+//   This library uses time0 and timer1.
+//   Note that timer0 may be repurposed when the first servo is attached.
+//
+//   Timers are seized as needed in groups of 12 servos - 24 servos use two
+//   timers, there are only two timers for the esp8266 so the support stops here
+//   The sequence used to sieze timers is defined in timers.h
+//
+//   The methods are:
+//
+//   Servo - Class for manipulating servo motors connected to Arduino pins.
+//
+//   attach(pin )  - Attaches a servo motor to an i/o pin.
+//   attach(pin, min, max  ) - Attaches to a pin setting min and max values in microseconds
+//   default min is 544, max is 2400
+//
+//   write()     - Sets the servo angle in degrees.  (invalid angle that is valid as pulse in microseconds is treated as microseconds)
+//   writeMicroseconds() - Sets the servo pulse width in microseconds
+//   read()      - Gets the last written servo pulse width as an angle between 0 and 180.
+//   readMicroseconds()   - Gets the last written servo pulse width in microseconds. (was read_us() in first release)
+//   attached()  - Returns true if there is a servo attached.
+//   detach()    - Stops an attached servos from pulsing its i/o pin.
+  
+
+#ifndef Servo_h
+#define Servo_h
+
+#include <Arduino.h>
+
+// the following are in us (microseconds)
+//
+#define MIN_PULSE_WIDTH       544     // the shortest pulse sent to a servo  
+#define MAX_PULSE_WIDTH      2400     // the longest pulse sent to a servo 
+#define DEFAULT_PULSE_WIDTH  1500     // default pulse width when servo is attached
+#define REFRESH_INTERVAL    20000     // minumim time to refresh servos in microseconds 
+
+// NOTE: to maintain a strict refresh interval the user needs to not exceede 8 servos 
+#define SERVOS_PER_TIMER       12     // the maximum number of servos controlled by one timer 
+#define MAX_SERVOS   (ServoTimerSequence_COUNT  * SERVOS_PER_TIMER)
+
+#if defined(ESP8266)
+
+#include "esp8266/ServoTimers.h"
+
+#else
+
+#error "This library only supports esp8266 boards."
+
+#endif
+
+class Servo
+{
+public:
+    Servo();
+    uint8_t attach(int pin);           // attach the given pin to the next free channel, sets pinMode, returns channel number or 0 if failure
+    uint8_t attach(int pin, int min, int max); // as above but also sets min and max values for writes. 
+    void detach();
+    void write(int value);             // if value is < 200 its treated as an angle, otherwise as pulse width in microseconds 
+    void writeMicroseconds(int value); // Write pulse width in microseconds 
+    int read();                        // returns current pulse width as an angle between 0 and 180 degrees
+    int readMicroseconds();            // returns current pulse width in microseconds for this servo (was read_us() in first release)
+    bool attached();                   // return true if this servo is attached, otherwise false 
+private:
+    uint8_t _servoIndex;               // index into the channel data for this servo
+    uint16_t _minUs;                   
+    uint16_t _maxUs;                   
+};
+
+#endif