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/drivers/drv_mixer.h

@@ -34,10 +34,20 @@
 /**
  * @file drv_mixer.h
  *
- * Mixer ioctl interface.
+ * Mixer ioctl interfaces.
  *
- * This interface can/should be exported by any device that supports
- * control -> actuator mixing.
+ * 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
@@ -46,51 +56,83 @@
 #include <stdint.h>
 #include <sys/ioctl.h>
 
-#include <systemlib/mixer.h>
-
-/**
- * Structure used for receiving mixers.
- *
- * Note that the mixers array is not actually an array of mixers; it
- * simply represents the first mixer in the buffer.
- */
-struct MixInfo {
-	unsigned	num_controls;
-	struct mixer_s	mixer;
-};
-
-/**
- * Handy macro for determining the allocation size of a MixInfo structure.
- */
-#define MIXINFO_SIZE(_num_controls)	(sizeof(struct MixInfo) + ((_num_controls) * sizeof(struct scaler_s)))
+#define MIXER_DEVICE_PATH		"/dev/mixer"
 
 /*
  * ioctl() definitions
  */
-
 #define _MIXERIOCBASE		(0x2400)
 #define _MIXERIOC(_n)		(_IOC(_MIXERIOCBASE, _n))
 
-/** get the number of actuators that require mixers in *(unsigned)arg */
-#define MIXERIOCGETMIXERCOUNT	_MIXERIOC(0)
+/** 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_input_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			input_count;	/**< number of inputs */
+	struct mixer_scaler_s	output_scaler;	/**< scaling for the output */
+	struct mixer_input_s	inputs[0];	/**< actual size of the array is set by input_count */
+};
+
+#define MIXER_SIMPLE_SIZE(_icount)	(sizeof(struct mixer_simple_s) + (_icount) * sizeof(struct mixer_input_s))
 
 /**
- * Copy a mixer from the device into *(struct MixInfo *)arg.
- *
- * The num_controls field indicates the number of controls for which space
- * is allocated following the MixInfo structure.  If the allocation
- * is too small, no mixer data is retured.  The control_count field in
- * the MixInfo.mixer structure is always updated.
- *
- * If no mixer is assigned for the given index, the ioctl returns ENOENT.
+ * add a simple mixer in (struct mixer_simple_s *)arg 
  */
-#define MIXERIOCGETMIXER(_mixer)	_MIXERIOC(0x20 + _mixer)
+#define MIXERIOCADDSIMPLE	_MIXERIOC(2)
+
+/** multirotor output definition */
+struct mixer_rotor_output_s
+{
+	float			angle;		/**< rotor angle clockwise from forward in radians */
+	float			distance;	/**< motor distance from centre in arbitrary units */
+};
+
+/** multirotor mixer */
+struct mixer_multirotor_s
+{
+	uint8_t			rotor_count;
+	struct mixer_input_s	inputs[4];	/**< inputs are roll, pitch, yaw, thrust */
+	struct mixer_rotor_output_s rotors[0];	/**< actual size of the array is set by rotor_count */
+};
 
 /**
- * Copy a mixer from *(struct mixer_s *)arg to the device.
- *
- * If arg is zero, the mixer is deleted.
+ * Add a multirotor mixer in (struct mixer_multirotor_s *)arg
+ */
+#define MIXERIOCADDMULTIROTOR	_MIXERIOC(3)
+
+/**
+ * Add mixers(s) from a the file in (const char *)arg
+ */
+#define MIXERIOCLOADFILE	_MIXERIOC(4)
+
+/*
+ * XXX Thoughts for additional operations:
+ *
+ * - get/set output scale, for tuning center/limit values.
+ * - save/serialise for saving tuned mixers.
  */
-#define MIXERIOCSETMIXER(_mixer)	_MIXERIOC(0x40 + _mixer)
 
 #endif /* _DRV_ACCEL_H */