Andreabont at 20:47, 22 April 2014

2014-04-22T20:47:02Z

← Older revision		Revision as of 20:47, 22 April 2014
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	The ''waitForCycleBegin()'' member function can be called by only one thread at a given time, so if you want to control more than one servo, be sure to put all the control code into only one loop. The other member functions are thread safe.		The ''waitForCycleBegin()'' member function can be called by only one thread at a given time, so if you want to control more than one servo, be sure to put all the control code into only one loop. The other member functions are thread safe.

			[[Category:API]]

Fede.tft: Created page with "Include statements and namespace required to use this library #include "drivers/servo_stm32.h" using namespace miosix; This is a C++ library, it ..."

2014-04-22T19:11:31Z

Created page with "Include statements and namespace required to use this library <source lang="CPP"> #include "drivers/servo_stm32.h" using namespace miosix; </source> This is a C++ library, it ..."

New page

Include statements and namespace required to use this library
<source lang="CPP">
#include "drivers/servo_stm32.h"
using namespace miosix;
</source>
This is a C++ library, it cannot be used from a C source file.

A servomotor is a device that allows to control the angular position of a shaft, like [https://www.sparkfun.com/products/10333 this one]. Servos work by reading a PWM signal with a fixed frequency, 50Hz by default, and a pulse period proportional to the desired angle.

== Supported boards ==

Miosix has a servo library that supports some boards using STM32 microcontrollers, namely the [[stm32f100rb_stm32vldiscovery]] and [[stm32f407vg_stm32f4discovery]].

== GPIO connection ==

The library supports up to 4 servo outputs, that must be connected to the following GPIOs (that the library configures as TIMER alternate function when the output is enabled).

* PB6 is the output 0
* PB7 is the output 1
* PB8 is the output 2
* PB9 is the output 3

== Library use ==

The library is a C++ class named ''SynchronizedServo''. It is a [https://en.wikipedia.org/wiki/Singleton_pattern singleton], so to instantiate it you have to call the ''instance()'' member function.

You can find examples on how to use the library in the [https://gitorious.org/miosix-kernel/miosix-kernel/source/0fb80132cd27fbd48021cd5a9adb21c90a9cb94e:miosix/_examples/servo miosix/_examples/servo] directory of the kernel.

=== Closed loop control support ===

If there is the need to run a closed loop control code using the servo as an actuator, the library supports a way to synchronize the controller with the servo waveform generation, using the ''waitForCycleBegin()'' member function in a loop. The value set with ''setPosition()'' will be output at the '''next''' cycle, so take into account the existence of a z^-1 in your plant model.

<source lang="CPP">
#include <stdio.h>
#include "drivers/servo_stm32.h"
using namespace miosix;

int main()
{
SynchronizedServo& servo=SynchronizedServo::instance();
servo.enable(0); //Enable channel 0 (connect servo to PB6)
servo.start();
for(;;)
{
//This loop will be executed 50 times a second, and be synchronized with the waveform generation
servo.waitForCycleBegin();
float pos=computeServoPosition();
servo.setPosition(0,pos);
}
}
</source>

== Thread safety considerations ==

The ''waitForCycleBegin()'' member function can be called by only one thread at a given time, so if you want to control more than one servo, be sure to put all the control code into only one loop. The other member functions are thread safe.

Servo tutorial - Revision history

Andreabont at 20:47, 22 April 2014

Fede.tft: Created page with "Include statements and namespace required to use this library #include "drivers/servo_stm32.h" using namespace miosix; This is a C++ library, it ..."