Rework the mixer architecture based on discussions about arbitrary geometry mixing and plugins.

Now the mixer is a C++ library that can be fairly easily bolted into an output driver to provide mixing services.

Teach the FMU driver how to use it as an example.  More testing is still required.

apps/systemlib/mixer/Makefile

@@ -0,0 +1,39 @@
+############################################################################
+#
+#   Copyright (C) 2012 PX4 Development Team. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in
+#    the documentation and/or other materials provided with the
+#    distribution.
+# 3. Neither the name PX4 nor the names of its contributors may be
+#    used to endorse or promote products derived from this software
+#    without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+# OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+############################################################################
+
+#
+# mixer library
+#
+LIBNAME	= mixerlib
+
+include $(APPDIR)/mk/app.mk

apps/systemlib/mixer/mixer.cpp

@@ -0,0 +1,211 @@
+/****************************************************************************
+ *
+ *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file mixer.cpp
+ *
+ * Programmable multi-channel mixer library.
+ */
+
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <errno.h>
+#include <stdio.h>
+#include <math.h>
+#include <unistd.h>
+
+#include "mixer.h"
+
+Mixer::Mixer(ControlCallback control_cb, uintptr_t cb_handle) :
+	_control_cb(control_cb),
+	_cb_handle(cb_handle)
+{
+}
+
+float
+Mixer::scale(const mixer_scaler_s &scaler, float input)
+{
+	float output;
+
+	if (input < 0.0f) {
+		output = (input * scaler.negative_scale) + scaler.offset;
+
+	} else {
+		output = (input * scaler.positive_scale) + scaler.offset;
+	}
+
+	if (output > scaler.max_output) {
+		output = scaler.max_output;
+
+	} else if (output < scaler.min_output) {
+		output = scaler.min_output;
+	}
+
+	return output;
+}
+
+int
+Mixer::scale_check(struct mixer_scaler_s &scaler)
+{
+	if (scaler.offset > 1.001f)
+		return 1;
+
+	if (scaler.offset < -1.001f)
+		return 2;
+
+	if (scaler.min_output > scaler.max_output)
+		return 3;
+
+	if (scaler.min_output < -1.001f)
+		return 4;
+
+	if (scaler.max_output > 1.001f)
+		return 5;
+
+	return 0;
+}
+
+/****************************************************************************/
+
+NullMixer::NullMixer() :
+	Mixer(nullptr, 0)
+{
+}
+
+unsigned
+NullMixer::mix(float *outputs, unsigned space)
+{
+	if (space > 0) {
+		*outputs = 0.0f;
+		return 1;
+	}
+	return 0;
+}
+
+void
+NullMixer::groups_required(uint32_t &groups)
+{
+
+}
+
+/****************************************************************************/
+
+SimpleMixer::SimpleMixer(ControlCallback control_cb,
+			 uintptr_t cb_handle,
+			 mixer_simple_s *mixinfo) :
+	Mixer(control_cb, cb_handle),
+	_info(mixinfo)
+{
+}
+
+SimpleMixer::~SimpleMixer()
+{
+	if (_info != nullptr)
+		free(_info);
+}
+
+unsigned
+SimpleMixer::mix(float *outputs, unsigned space)
+{
+	float		sum = 0.0f;
+
+	if (_info == nullptr)
+		return 0;
+	if (space < 1)
+		return 0;
+
+	for (unsigned i = 0; i < _info->input_count; i++) {
+		float input;
+
+		_control_cb(_cb_handle,
+			    _info->inputs[i].control_group,
+			    _info->inputs[i].control_index,
+			    input);
+
+		sum += scale(_info->inputs[i].scaler, input);
+	}
+	*outputs = scale(_info->output_scaler, sum);
+	return 1;
+}
+
+void
+SimpleMixer::groups_required(uint32_t &groups)
+{
+	for (unsigned i = 0; i < _info->input_count; i++)
+		groups |= 1 << _info->inputs[i].control_group;
+}
+
+int
+SimpleMixer::check()
+{
+	int ret;
+	float junk;
+
+	/* sanity that presumes that a mixer includes a control no more than once */
+	/* max of 32 groups due to groups_required API */
+	if (_info->input_count > 32)
+		return -2;
+
+	/* validate the output scaler */
+	ret = scale_check(_info->output_scaler);
+
+	if (ret != 0)
+		return ret;
+
+	/* validate input scalers */
+	for (unsigned i = 0; i < _info->input_count; i++) {
+
+		/* verify that we can fetch the control */
+		if (_control_cb(_cb_handle,
+				_info->inputs[i].control_group,
+				_info->inputs[i].control_index,
+				junk) != 0) {
+			return -3;
+		}
+
+		/* validate the scaler */
+		ret = scale_check(_info->inputs[i].scaler);
+
+		if (ret != 0)
+			return (10 * i + ret);
+	}
+
+	return 0;
+}

apps/systemlib/mixer/mixer.h

@@ -0,0 +1,358 @@
+/****************************************************************************
+ *
+ *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @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

apps/systemlib/mixer/mixer_group.cpp

@@ -0,0 +1,288 @@
+/****************************************************************************
+ *
+ *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file mixer_group.cpp
+ *
+ * Mixer collection.
+ */
+
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <errno.h>
+#include <stdio.h>
+#include <math.h>
+#include <unistd.h>
+
+#include "mixer.h"
+
+namespace
+{
+
+/**
+ * Effectively fdgets() with some extra smarts.
+ */
+static int
+mixer_getline(int fd, char *line, unsigned maxlen)
+{
+	/* reduce line budget by 1 to account for terminal NUL */
+	maxlen--;
+
+	/* loop looking for a non-comment line */
+	for (;;) {
+		int	ret;
+		char	c;
+		char	*p = line;
+
+		/* loop reading characters for this line */
+		for (;;) {
+			ret = read(fd, &c, 1);
+
+			/* on error or EOF, return same */
+			if (ret <= 0)
+				return ret;
+
+			/* ignore carriage returns */
+			if (c == '\r')
+				continue;
+
+			/* line termination */
+			if (c == '\n') {
+				/* ignore malformed lines */
+				if ((p - line) < 4)
+					break;
+
+				if (line[1] != ':')
+					break;
+
+				/* terminate line as string and return */
+				*p = '\0';
+				return 1;
+			}
+
+			/* if we have space, accumulate the byte and go on */
+			if ((p - line) < maxlen)
+				*p++ = c;
+		}
+	}
+}
+
+/**
+ * Parse a scaler from the buffer.
+ */
+static int
+mixer_parse_scaler(const char *buf, mixer_scaler_s &scaler, uint8_t &control_group, uint8_t &control_index)
+{
+	unsigned u[2];
+	int s[5];
+
+	if (sscanf(buf, "S: %u %u %d %d %d %d %d",
+		   &u[0], &u[1], &s[0], &s[1], &s[2], &s[3], &s[4]) != 7)
+		return -1;
+
+	control_group	= u[0];
+	control_index	= u[1];
+	scaler.negative_scale	= s[0] / 10000.0f;
+	scaler.positive_scale	= s[1] / 10000.0f;
+	scaler.offset		= s[2] / 10000.0f;
+	scaler.min_output	= s[3] / 10000.0f;
+	scaler.max_output	= s[4] / 10000.0f;
+
+	return 0;
+}
+
+SimpleMixer *
+mixer_load_simple(Mixer::ControlCallback control_cb, uintptr_t cb_handle, int fd, unsigned inputs)
+{
+	mixer_simple_s	*mixinfo = nullptr;
+	char		buf[60];
+	uint8_t		control_group, control_index;
+	int		ret;
+
+	/* let's assume we're going to read a simple mixer */
+	mixinfo = (mixer_simple_s *)malloc(MIXER_SIMPLE_SIZE(inputs));
+
+	/* first, get the output scaler */
+	ret = mixer_getline(fd, buf, sizeof(buf));
+	if (ret < 1)
+		goto fail;
+	if (mixer_parse_scaler(buf, mixinfo->output_scaler, control_group, control_index))
+		goto fail;
+
+	/* now get any inputs */
+	for (unsigned i = 0; i < inputs; i++) {
+		ret = mixer_getline(fd, buf, sizeof(buf));
+		if (ret < 1)
+			goto fail;
+		if (mixer_parse_scaler(buf, 
+				       mixinfo->inputs[i].scaler,
+				       mixinfo->inputs[i].control_group,
+				       mixinfo->inputs[i].control_index)) {
+			goto fail;
+		}
+	}
+
+	/* XXX should be a factory that validates the mixinfo ... */
+	return new SimpleMixer(control_cb, cb_handle, mixinfo);
+
+fail:
+	free(mixinfo);
+	return nullptr;
+}
+
+int
+mixer_load(Mixer::ControlCallback control_cb, uintptr_t cb_handle, int fd, Mixer *&mixer)
+{
+	int		ret;
+	char		buf[60];
+	unsigned	scalers;
+
+	ret = mixer_getline(fd, buf, sizeof(buf));
+
+	/* end of file or error ?*/
+	if (ret < 1)
+		return ret;
+
+	/* slot is empty - allocate a null mixer */
+	if (buf[0] == 'Z') {
+		mixer = new NullMixer();
+		return 0;
+	}
+
+	/* is it a simple mixer? */
+	if (sscanf(buf, "M: %u", &scalers) == 1) {
+		mixer = mixer_load_simple(control_cb, cb_handle, fd, scalers);
+		return (mixer == nullptr) ? -1 : 0;
+	}
+
+	/* we don't recognise the mixer type */
+	return -1;
+}
+
+
+} // namespace
+
+MixerGroup::MixerGroup(ControlCallback control_cb, uintptr_t cb_handle) :
+	Mixer(control_cb, cb_handle),
+	_first(nullptr)
+{
+}
+
+MixerGroup::~MixerGroup()
+{
+	Mixer *mixer;
+
+	/* discard sub-mixers */
+	while (_first != nullptr) {
+		mixer = _first;
+		_first = mixer->_next;
+		delete mixer;
+	}
+}
+
+void
+MixerGroup::add_mixer(Mixer *mixer)
+{
+	Mixer **mpp;
+
+	mpp = &_first;
+	while (*mpp != nullptr)
+		mpp = &((*mpp)->_next);
+	*mpp = mixer;
+	mixer->_next = nullptr;
+}
+
+unsigned
+MixerGroup::mix(float *outputs, unsigned space)
+{
+	Mixer	*mixer = _first;
+	unsigned index = 0;
+
+	while ((mixer != nullptr) && (index < space)) {
+		index += mixer->mix(outputs + index, space - index);
+		mixer = mixer->_next;
+	}
+	return index;
+}
+
+void
+MixerGroup::groups_required(uint32_t &groups)
+{
+	Mixer	*mixer = _first;
+
+	while (mixer != nullptr) {
+		mixer->groups_required(groups);
+		mixer = mixer->_next;
+	}
+}
+
+int
+MixerGroup::load_from_file(const char *path)
+{
+	if (_first != nullptr)
+		return -1;
+
+	int fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	for (;;) {
+		int	result;
+		Mixer	*mixer;
+
+		result = mixer_load(_control_cb,
+				    _cb_handle,
+				    fd,
+				    mixer);
+
+		/* error? */
+		if (result < 0)
+			return -1;
+
+		/* EOF or error */
+		if (result < 1)
+			break;
+
+		add_mixer(mixer);
+	}
+
+	close(fd);
+	return 0;
+}

apps/systemlib/mixer/mixer_multirotor.cpp

@@ -0,0 +1,81 @@
+/****************************************************************************
+ *
+ *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file mixer_multirotor.cpp
+ *
+ * Multi-rotor mixers.
+ */
+
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <errno.h>
+#include <stdio.h>
+#include <math.h>
+#include <unistd.h>
+
+#include "mixer.h"
+
+MultirotorMixer::MultirotorMixer(ControlCallback control_cb,
+				 uintptr_t cb_handle,
+				 MultirotorMixer::Geometry geom) :
+	Mixer(control_cb, cb_handle),
+	_geometry(geom)
+{
+}
+
+MultirotorMixer::~MultirotorMixer()
+{
+}
+
+unsigned
+MultirotorMixer::mix(float *outputs, unsigned space)
+{
+	/* XXX implement this */
+	return 0;
+}
+
+void
+MultirotorMixer::groups_required(uint32_t &groups)
+{
+	/* XXX for now, hardcoded to indexes 0-3 in control group zero */
+	groups |= (1 << 0);
+}
+