Servo lib works, *but* within the scope of the following... (From the Servo.h comments)
/*
* 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 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, your board's pin map is your friend.
*/
In other words, you can have more servos than the default Arduino Servo lib provides for (12 on the STM, but only two on an Arduino) but they must be on STM32 PWM pins... on the STM32 according to the Maple Mini documentation PWM pins are 3, 4, 5, 8, 9, 10, 11, 15, 16, 25, 26, 27
I tested with a servo in PIN 3 (D3 -> PB0 on my clone board) and this sketch.
// Sweep
// by BARRAGAN <http://barraganstudio.com>
// This example code is in the public domain.
#include <Servo.h>
// For STM32 testing...
// Note: on the STM32 PWM pins are 3, 4, 5, 8, 9, 10, 11, 15, 16, 25, 26, 27
#define SERVO 3
Servo myservo; // create servo object to control a servo
int pos = 0; // variable to store the servo position
void setup()
{
myservo.attach(SERVO); // attaches the servo on pin XX to the servo object
// on an AVR Arduino this is either 9 or 10
// on the STM32
}
void loop()
{
for(pos = 0; pos < 180; pos += 1) // goes from 0 degrees to 180 degrees
{ // in steps of 1 degree
myservo.write(pos); // tell servo to go to position in variable 'pos'
delay(15); // waits 15ms for the servo to reach the position
}
for(pos = 180; pos>=1; pos-=1) // goes from 180 degrees to 0 degrees
{
myservo.write(pos); // tell servo to go to position in variable 'pos'
delay(15); // waits 15ms for the servo to reach the position
}
}
NOTE: I only tested on pin 3, due to lack of time, but have no reason to suppose there will be any problem with using the other PWM pins. The waveform on my oscilloscope look correct but are obviously only 3v3, which my servo is quite happy with.
For the record, the servo used in the test was a
very cheap 9g "Micro Servo".. this sort of thing.If you don't already have a few of these lying around, get them, they are very useful.
