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diff --git a/src/drivers/drv_mixer.h b/src/drivers/drv_mixer.h
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+/****************************************************************************
+ *
+ *   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 drv_mixer.h
+ *
+ * Mixer ioctl interfaces.
+ *
+ * Normal workflow is:
+ *
+ * - open mixer device
+ * - add mixer(s)
+ * loop:
+ *  - mix actuators to array
+ *
+ * Each client has its own configuration.
+ *
+ * When mixing, outputs are produced by mixers in the order they are
+ * added.  A simple mixer produces one output; a multotor mixer will
+ * produce several outputs, etc.
+ */
+
+#ifndef _DRV_MIXER_H
+#define _DRV_MIXER_H
+
+#include <stdint.h>
+#include <sys/ioctl.h>
+
+#define MIXER_DEVICE_PATH		"/dev/mixer"
+
+/*
+ * ioctl() definitions
+ */
+#define _MIXERIOCBASE		(0x2500)
+#define _MIXERIOC(_n)		(_IOC(_MIXERIOCBASE, _n))
+
+/** get the number of mixable outputs */
+#define MIXERIOCGETOUTPUTCOUNT	_MIXERIOC(0)
+
+/** reset (clear) the mixer configuration */
+#define MIXERIOCRESET		_MIXERIOC(1)
+
+/** simple channel scaler */
+struct mixer_scaler_s {
+	float			negative_scale;
+	float			positive_scale;
+	float			offset;
+	float			min_output;
+	float			max_output;
+};
+
+/** mixer input */
+struct mixer_control_s {
+	uint8_t			control_group;	/**< group from which the input reads */
+	uint8_t			control_index;	/**< index within the control group */
+	struct mixer_scaler_s 	scaler;		/**< scaling applied to the input before use */
+};
+
+/** simple mixer */
+struct mixer_simple_s {
+	uint8_t			control_count;	/**< number of inputs */
+	struct mixer_scaler_s	output_scaler;	/**< scaling for the output */
+	struct mixer_control_s	controls[0];	/**< actual size of the array is set by control_count */
+};
+
+#define MIXER_SIMPLE_SIZE(_icount)	(sizeof(struct mixer_simple_s) + (_icount) * sizeof(struct mixer_control_s))
+
+/**
+ * add a simple mixer in (struct mixer_simple_s *)arg
+ */
+#define MIXERIOCADDSIMPLE	_MIXERIOC(2)
+
+/* _MIXERIOC(3) was deprecated */
+/* _MIXERIOC(4) was deprecated */
+
+/**
+ * Add mixer(s) from the buffer in (const char *)arg
+ */
+#define MIXERIOCLOADBUF		_MIXERIOC(5)
+
+/*
+ * XXX Thoughts for additional operations:
+ *
+ * - get/set output scale, for tuning center/limit values.
+ * - save/serialise for saving tuned mixers.
+ */
+
+#endif /* _DRV_ACCEL_H */