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/**
 * @file mixer.h
 *
 * Generic, programmable, procedural control signal mixers.
 *
 * This library implements a generic mixer interface that can be used
 * by any driver or subsytem that wants to combine several control signals
 * into a single output.
 *
 * Terminology
 * ===========
 *
 * control value
 *	A mixer input value, typically provided by some controlling
 *	component of the system.
 *
 * control group
 * 	A collection of controls provided by a single controlling component.
 *
 * actuator
 *	The mixer output value.
 *
 *
 * Mixing basics
 * =============
 *
 * An actuator derives its value from the combination of one or more
 * control values. Each of the control values is scaled according to
 * the actuator's configuration and then combined to produce the
 * actuator value, which may then be further scaled to suit the specific
 * output type.
 *
 * Internally, all scaling is performed using floating point values.
 * Inputs and outputs are clamped to the range -1.0 to 1.0.
 *
 * control    control   control
 *    |          |         |
 *    v          v         v
 *  scale      scale     scale
 *    |          |         |
 *    |          v         |
 *    +-------> mix <------+
 *               |
 *             scale
 *               |
 *               v
 *              out
 *
 * Scaling
 * -------
 *
 * Each scaler allows the input value to be scaled independently for
 * inputs greater/less than zero. An offset can be applied to the output,
 * as well as lower and upper boundary constraints.
 * Negative scaling factors cause the output to be inverted (negative input
 * produces positive output).
 *
 * Scaler pseudocode:
 *
 * if (input < 0)
 *     output = (input * NEGATIVE_SCALE) + OFFSET
 * else
 *     output = (input * POSITIVE_SCALE) + OFFSET
 *
 * if (output < LOWER_LIMIT)
 *     output = LOWER_LIMIT
 * if (output > UPPER_LIMIT)
 *     output = UPPER_LIMIT
 *
 *
 * Mixing
 * ------
 *
 * Mixing behaviour varies based on the specific mixer class; each
 * mixer class describes its behaviour in more detail.
 *
 *
 * Controls
 * --------
 *
 * The precise assignment of controls may vary depending on the
 * application, but the following assignments should be used
 * when appropriate.  Some mixer classes have specific assumptions
 * about the assignment of controls.
 *
 * control | standard meaning
 * --------+-----------------------
 *     0   | roll
 *     1   | pitch
 *     2   | yaw
 *     3   | primary thrust
 */


#ifndef _SYSTEMLIB_MIXER_MIXER_H
#define _SYSTEMLIB_MIXER_MIXER_H value

#include "drivers/drv_mixer.h"

/**
 * Abstract class defining a mixer mixing zero or more inputs to 
 * one or more outputs.
 */
class __EXPORT Mixer
{
public:
	/** next mixer in a list */
	Mixer				*_next;

	/**
	 * Fetch a control value.
	 *
	 * @param handle		Token passed when the callback is registered.
	 * @param control_group		The group to fetch the control from.
	 * @param control_index		The group-relative index to fetch the control from.
	 * @param control		The returned control
	 * @return			Zero if the value was fetched, nonzero otherwise.
	 */
	typedef int			(* ControlCallback)(uintptr_t handle,
							    uint8_t control_group,
							    uint8_t control_index,
							    float &control);

	/**
	 * Constructor.
	 *
	 * @param control_cb		Callback invoked when reading controls.
	 */
	Mixer(ControlCallback control_cb, uintptr_t cb_handle);
	~Mixer() {};

	/**
	 * Perform the mixing function.
	 *
	 * @param outputs		Array into which mixed output(s) should be placed.
	 * @param space			The number of available entries in the output array;
	 * @return			The number of entries in the output array that were populated.
	 */
	virtual unsigned		mix(float *outputs, unsigned space) = 0;

	/**
	 * Analyses the mix configuration and updates a bitmask of groups
	 * that are required.
	 *
	 * @param groups		A bitmask of groups (0-31) that the mixer requires.
	 */
	virtual void			groups_required(uint32_t &groups) = 0;

protected:
	/** client-supplied callback used when fetching control values */
	ControlCallback			_control_cb;
	uintptr_t			_cb_handle;

	/**
	 * Perform simpler linear scaling.
	 *
	 * @param scaler		The scaler configuration.
	 * @param input			The value to be scaled.
	 * @return			The scaled value.
	 */
	static float			scale(const mixer_scaler_s &scaler, float input);

	/**
	 * Validate a scaler
	 *
	 * @param scaler		The scaler to be validated.
	 * @return			Zero if good, nonzero otherwise.
	 */
	static int			scale_check(struct mixer_scaler_s &scaler);

private:
};

/**
 * Group of mixers, built up from single mixers and processed
 * in order when mixing.
 */
class __EXPORT MixerGroup : public Mixer
{
public:
	MixerGroup(ControlCallback control_cb, uintptr_t cb_handle);
	~MixerGroup();

	virtual unsigned		mix(float *outputs, unsigned space);
	virtual void			groups_required(uint32_t &groups);

	/**
	 * Add a mixer to the group.
	 *
	 * @param mixer			The mixer to be added.
	 */
	void				add_mixer(Mixer *mixer);

	/**
	 * Reads a mixer definition from a file and configures a corresponding
	 * group.
	 *
	 * The mixer group must be empty when this function is called.
	 *
	 * A mixer definition is a text representation of the configuration of a
	 * mixer. Definition lines begin with a capital letter followed by a colon.
	 *
	 * Null Mixer:
	 *
	 * Z:
	 *
	 * This mixer generates a constant zero output, and is normally used to 
	 * skip over outputs that are not in use. 
	 *
	 * Simple Mixer:
	 *
	 * M: <scaler count>
	 * S: <control group> <control index> <negative_scale*> <positive_scale*> <offset*> <lower_limit*> <upper_limit*>
	 * S: ...
	 *
	 * The definition consists of a single-line header indicating the
	 * number of scalers and then one line defining each scaler.  The first
	 * scaler in the file is always the output scaler, followed by the input
	 * scalers.
	 *
	 * The <control ...> values for the output scaler are ignored by the mixer.
	 *
	 *
	 *
	 * Values marked * are integers representing floating point values; values are
	 * scaled by 10000 on load/save.
	 *
	 * Multiple mixer definitions may be stored in a single file; it is assumed that
	 * the reader will know how many to expect and read accordingly.
	 *
	 * A mixer entry with a scaler count of zero indicates a disabled mixer. This
	 * will return NULL for the mixer when processed by this function, and will be
	 * generated by passing NULL as the mixer to mixer_save.
	 *
	 * @param path			The mixer configuration file to read.
	 * @return			Zero on successful load, nonzero otherwise.
	 */
	int				load_from_file(const char *path);

private:
	Mixer				*_first;	/**< linked list of mixers */
};

/**
 * Null mixer; returns zero.
 *
 * Used as a placeholder for output channels that are unassigned in groups.
 */
class __EXPORT NullMixer : public Mixer
{
public:
	NullMixer();
	~NullMixer() {};

	virtual unsigned		mix(float *outputs, unsigned space);
	virtual void			groups_required(uint32_t &groups);
};

/**
 * Simple summing mixer.
 *
 * Collects zero or more inputs and mixes them to a single output.
 */
class __EXPORT SimpleMixer : public Mixer
{
public:
	/**
	 * Constructor
	 *
	 * @param mixinfo		Mixer configuration.  The pointer passed
	 *				becomes the property of the mixer and
	 *				will be freed when the mixer is deleted.
	 */
	SimpleMixer(ControlCallback control_cb,
		    uintptr_t cb_handle,
		    mixer_simple_s *mixinfo);
	~SimpleMixer();

	virtual unsigned		mix(float *outputs, unsigned space);
	virtual void			groups_required(uint32_t &groups);

	/**
	 * Check that the mixer configuration as loaded is sensible.
	 *
	 * Note that this function will call control_cb, but only cares about
	 * error returns, not the input value.
	 *
	 * @return			Zero if the mixer makes sense, nonzero otherwise.
	 */
	int				check();
protected:

private:
	mixer_simple_s		*_info;
};

/**
 * Multi-rotor mixer.
 *
 * Collects four inputs (roll, pitch, yaw, thrust) and mixes them to
 * a set of outputs based on the configured geometry.
 */
class __EXPORT MultirotorMixer : public Mixer
{
public:
	enum Geometry
	{
		MULTIROTOR_QUAD_PLUS,
		MULTIROTOR_QUAD_X
		/* XXX add more here */
	};

	MultirotorMixer(ControlCallback control_cb,
			uintptr_t cb_handle,
			Geometry geom);
	~MultirotorMixer();

	virtual unsigned		mix(float *outputs, unsigned space);
	virtual void			groups_required(uint32_t &groups);

private:
	Geometry			_geometry;
};

#endif