hsk_filter.h

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/** \file
 * HSK Filter generator
 *
 * This file offers preprocessor macros to filter analogue values, by
 * calculating the average of a set of a given length.
 *
 * The buffer for the filter is stored in xdata memory.
 *
 * @author kami
 */

#ifndef _HSK_FILTER_H_
#define _HSK_FILTER_H_

#include <Infineon/XC878.h>

#include <string.h> /* memset() */

/**
 * Generates a filter.
 *
 * The filter can be accessed with:
 * - void <prefix>_init(void)
 *      - Initializes the filter with 0
 * - <valueType> <prefix>_update(const <valueType> value)
 *      - Update the filter and return the current average
 *
 * @param prefix
 *      A prefix for the generated internals and functions
 * @param valueType
 *      The data type of the stored values
 * @param sumType
 *      A data type that can contain the sum of all buffered values
 * @param sizeType
 *      A data type that can hold the length of the buffer
 * @param size
 *      The length of the buffer
 */
#define FILTER_FACTORY(prefix, valueType, sumType, sizeType, size) \
        \
        /**
         * Holds the buffer and its current state.
         */ \
        struct { \
                /**
                 * The value buffer.
                 */ \
                valueType values[size]; \
        \
                /**
                 * The sum of the buffered values.
                 */ \
                sumType sum; \
        \
                /**
                 * The index of the oldest buffered value.
                 */ \
                sizeType current; \
        } xdata prefix; \
        \
        /**
         * Initializes the buffer with 0.
         */ \
        void prefix##_init(void) { \
                memset(&prefix, 0, sizeof(prefix)); \
        } \
        \
        /**
         * Updates the filter and returns the current sliding average of
         * buffered values.
         *
         * @param value
         *      The value to add to the buffer
         * @return
         *      The average of the buffed values
         */ \
        valueType prefix##_update(const valueType value) { \
                prefix.sum -= prefix.values[prefix.current]; \
                prefix.values[prefix.current++] = value; \
                prefix.sum += value; \
                prefix.current %= size; \
                return prefix.sum / size; \
        } \


/**
 * Generates a group of filters.
 *
 * The filters can be accessed with:
 * - void <prefix>_init(void)
 *      - Initializes all filters with 0
 * - <valueType> <prefix>_update(const ubyte filter, const <valueType> value)
 *      - Update the given filter and return the current average
 *
 * @param prefix
 *      A prefix for the generated internals and functions
 * @param filters
 *      The number of filters
 * @param valueType
 *      The data type of the stored values
 * @param sumType
 *      A data type that can contain the sum of all buffered values
 * @param sizeType
 *      A data type that can hold the length of the buffer
 * @param size
 *      The length of the buffer
 */
#define FILTER_GROUP_FACTORY(prefix, filters, valueType, sumType, sizeType, size) \
        \
        /**
         * Holds the buffers and their current states.
         */ \
        struct { \
                /**
                 * The value buffer.
                 */ \
                valueType values[size]; \
        \
                /**
                 * The sum of the buffered values.
                 */ \
                sumType sum; \
        \
                /**
                 * The index of the oldest buffered value.
                 */ \
                sizeType current; \
        } xdata prefix[filters]; \
        \
        /**
         * Initializes all buffers with 0.
         */ \
        void prefix##_init(void) { \
                memset(&prefix, 0, sizeof(prefix)); \
        } \
        \
        /**
         * Updates the given filter and returns the current sliding average of
         * buffered values.
         *
         * @param filter
         *      The filter to update
         * @param value
         *      The value to add to the buffer
         * @return
         *      The average of the buffed values
         */ \
        valueType prefix##_update(const ubyte filter, const valueType value) { \
                prefix[filter].sum -= prefix[filter].values[prefix[filter].current]; \
                prefix[filter].values[prefix[filter].current++] = value; \
                prefix[filter].sum += value; \
                prefix[filter].current %= size; \
                return prefix[filter].sum / size; \
        } \


#endif /* _HSK_FILTER_H_ */