Servo: Calling write() before attach() causes problems

[chrisfraser]

In other servo libraries calling write() or writeMicroseconds() before attach sets the initial position of the servo on attach.

This causes the servo to not work in the latest staging release. See code to reproduce below.

#include <Servo.h>

Servo servo;

int servoPin = 13;

void setup()
{
  servo.writeMicroseconds(544);

  servo.attach(servoPin);

  delay(3000);
}

void loop()
{
  int us;

  for (us = 544; us <= 2400; us += 2)
  {
    servo.writeMicroseconds(us);
    delay(3);
  }
  for (us = 2400; us >= 544; us -= 2)
  {
    servo.write(us);
    delay(3);
  }
}

[chrisfraser]

Upon further investigation, the _minUs and _maxUs variables are only initialised in attach(). This means that the values are 0 when calling write().

In write() the value will evaluate to 0.

value = map(value, 0, 180, _minUs, _maxUs);

In writeMicroseconds() the value will evaluate to 0 too.

value = max(_minUs, min(_maxUs, value));

Will create a pull request.