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/**
* @file mixer.h
*
* Generic control value mixing library.
*
* This library implements a generic mixer function that can be used
* by any driver or subsytem that wants to combine several control signals
* into a single output.
*
* Terminology
* ===========
*
* control
* A mixer input value, typically provided by some controlling
* component of the system.
*
* 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 is performed by summing the scaled control values.
*
*
* Controls
* --------
*
* Each mixer is presented with an array of controls from which it
* selects the set that will be mixed for each actuator.
*
* The precise assignment of controls may vary depending on the
* application, but the following assignments should be used
* when appropriate.
*
* control | standard meaning
* --------+-----------------------
* 0 | roll
* 1 | pitch
* 2 | yaw
* 3 | primary thrust
*/
struct MixScaler
{
unsigned control; /**< control consumed by this scaler */
float negative_scale; /**< scale for inputs < 0 */
float positive_scale; /**< scale for inputs > 0 */
float offset; /**< bias applied to output */
float lower_limit; /**< minimum output value */
float upper_limit; /**< maximum output value */
};
struct MixMixer
{
unsigned control_count; /**< number of control scalers */
struct MixScaler output_scaler; /**< scaler applied to mixer output */
struct MixScaler control_scaler[0]; /**< array of control scalers */
};
__BEGIN_DECLS
/**
* Perform a mixer calculation.
*
* Note that the controls array is assumed to be sufficiently large for any control
* index in the mixer.
*
* @param mixer Mixer configuration.
* @param controls Array of input control values.
* @return The mixed output.
*/
__EXPORT float mixer_mix(struct MixMixer *mixer, float *controls);
/**
* Check a mixer configuration for sanity.
*
* @param mixer The mixer configuration to be checked.
* @param control_count The number of controls in the system.
* @return Zero if the mixer configuration is sane,
* nonzero otherwise.
*/
__EXPORT int mixer_check(struct MixMixer *mixer, unsigned control_count);
__END_DECLS
