param.h

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/**
 * @file param.h
 *
 * Global parameter store.
 *
 * Note that a number of API members are marked const or pure; these
 * assume that the set of parameters cannot change, or that a parameter
 * cannot change type or size over its lifetime.  If any of these assumptions
 * are invalidated, the attributes should be re-evaluated.
 */

#ifndef _SYSTEMLIB_PARAM_PARAM_H
#define _SYSTEMLIB_PARAM_PARAM_H

#include <stdint.h>
#include <stdbool.h>
#include <sys/types.h>

/** Maximum size of the parameter backing file */
#define PARAM_FILE_MAXSIZE      4096

__BEGIN_DECLS

/**
 * Parameter types.
 */
#define PARAM_TYPE_INT32        0
#define PARAM_TYPE_FLOAT        1
#define PARAM_TYPE_STRUCT       100
#define PARAM_TYPE_STRUCT_MAX   (16384 + PARAM_TYPE_STRUCT)
#define PARAM_TYPE_UNKNOWN      (0xffff)

typedef uint16_t param_type_t;


#ifdef __PX4_NUTTX // on NuttX use 16 bits to save RAM
/**
 * Parameter handle.
 *
 * Parameters are represented by parameter handles, which can
 * be obtained by looking up parameters. They are an offset into a global
 * constant parameter array.
 */
typedef uint16_t    param_t;

/**
 * Handle returned when a parameter cannot be found.
 */
#define PARAM_INVALID   ((uint16_t)0xffff)

/**
 * Magic handle for hash check param
 */
#define PARAM_HASH      ((uint16_t)INT16_MAX)

#else // on other platforms use 32 bits for better performance

/**
 * Parameter handle.
 *
 * Parameters are represented by parameter handles, which can
 * be obtained by looking up parameters. They are an offset into a global
 * constant parameter array.
 */
typedef uint32_t    param_t;

/**
 * Handle returned when a parameter cannot be found.
 */
#define PARAM_INVALID   ((uint32_t)0xffffffff)

/**
 * Magic handle for hash check param
 */
#define PARAM_HASH      ((uint32_t)INT32_MAX)

#endif /* __PX4_NUTTX */


/**
 * Initialize the param backend. Call this on startup before calling any other methods.
 */
__EXPORT void       param_init(void);

/**
 * Look up a parameter by name.
 *
 * @param name      The canonical name of the parameter being looked up.
 * @return      A handle to the parameter, or PARAM_INVALID if the parameter does not exist.
 *          This call will also set the parameter as "used" in the system, which is used
 *          to e.g. show the parameter via the RC interface
 */
__EXPORT param_t    param_find(const char *name);

/**
 * Look up a parameter by name.
 *
 * @param name      The canonical name of the parameter being looked up.
 * @return      A handle to the parameter, or PARAM_INVALID if the parameter does not exist.
 */
__EXPORT param_t    param_find_no_notification(const char *name);

/**
 * Return the total number of parameters.
 *
 * @return      The number of parameters.
 */
__EXPORT unsigned   param_count(void);

/**
 * Return the actually used number of parameters.
 *
 * @return      The number of parameters.
 */
__EXPORT unsigned   param_count_used(void);

/**
 * Wether a parameter is in use in the system.
 *
 * @return      True if it has been written or read
 */
__EXPORT bool       param_used(param_t param);

/**
 * Look up a parameter by index.
 *
 * @param index     An index from 0 to n, where n is param_count()-1.
 * @return      A handle to the parameter, or PARAM_INVALID if the index is out of range.
 */
__EXPORT param_t    param_for_index(unsigned index);

/**
 * Look up an used parameter by index.
 *
 * @param index     The parameter to obtain the index for.
 * @return      The index of the parameter in use, or -1 if the parameter does not exist.
 */
__EXPORT param_t    param_for_used_index(unsigned index);

/**
 * Look up the index of a parameter.
 *
 * @param param     The parameter to obtain the index for.
 * @return      The index, or -1 if the parameter does not exist.
 */
__EXPORT int        param_get_index(param_t param);

/**
 * Look up the index of an used parameter.
 *
 * @param param     The parameter to obtain the index for.
 * @return      The index of the parameter in use, or -1 if the parameter does not exist.
 */
__EXPORT int        param_get_used_index(param_t param);

/**
 * Obtain the name of a parameter.
 *
 * @param param     A handle returned by param_find or passed by param_foreach.
 * @return      The name assigned to the parameter, or NULL if the handle is invalid.
 */
__EXPORT const char *param_name(param_t param);

/**
 * Obtain the volatile state of a parameter.
 *
 * @param param     A handle returned by param_find or passed by param_foreach.
 * @return          true if the parameter is volatile
 */
__EXPORT bool       param_is_volatile(param_t param);

/**
 * Test whether a parameter's value has changed from the default.
 *
 * @return      If true, the parameter's value has not been changed from the default.
 */
__EXPORT bool       param_value_is_default(param_t param);

/**
 * Test whether a parameter's value has been changed but not saved.
 *
 * @return      If true, the parameter's value has not been saved.
 */
__EXPORT bool       param_value_unsaved(param_t param);

/**
 * Obtain the type of a parameter.
 *
 * @param param     A handle returned by param_find or passed by param_foreach.
 * @return      The type assigned to the parameter.
 */
__EXPORT param_type_t   param_type(param_t param);

/**
 * Determine the size of a parameter.
 *
 * @param param     A handle returned by param_find or passed by param_foreach.
 * @return      The size of the parameter's value.
 */
__EXPORT size_t     param_size(param_t param);

/**
 * Copy the value of a parameter.
 *
 * @param param     A handle returned by param_find or passed by param_foreach.
 * @param val       Where to return the value, assumed to point to suitable storage for the parameter type.
 *          For structures, a bitwise copy of the structure is performed to this address.
 * @return      Zero if the parameter's value could be returned, nonzero otherwise.
 */
__EXPORT int        param_get(param_t param, void *val);

/**
 * Set the value of a parameter.
 *
 * @param param     A handle returned by param_find or passed by param_foreach.
 * @param val       The value to set; assumed to point to a variable of the parameter type.
 *          For structures, the pointer is assumed to point to a structure to be copied.
 * @return      Zero if the parameter's value could be set from a scalar, nonzero otherwise.
 */
__EXPORT int        param_set(param_t param, const void *val);

/**
 * Mark a parameter as used. Only marked parameters will be sent to a GCS.
 * A call to param_find() will mark a param as used as well.
 *
 * @param param     A handle returned by param_find or passed by param_foreach.
 */
__EXPORT void       param_set_used(param_t param);

/**
 * Set the value of a parameter, but do not notify the system about the change.
 *
 * @param param     A handle returned by param_find or passed by param_foreach.
 * @param val       The value to set; assumed to point to a variable of the parameter type.
 *          For structures, the pointer is assumed to point to a structure to be copied.
 * @return      Zero if the parameter's value could be set from a scalar, nonzero otherwise.
 */
__EXPORT int        param_set_no_notification(param_t param, const void *val);

/**
 * Notify the system about parameter changes. Can be used for example after several calls to
 * param_set_no_notification() to avoid unnecessary system notifications.
 */
__EXPORT void       param_notify_changes(void);

/**
 * Reset a parameter to its default value.
 *
 * This function frees any storage used by struct parameters, and returns the parameter
 * to its default value.
 *
 * @param param     A handle returned by param_find or passed by param_foreach.
 * @return      Zero on success, nonzero on failure
 */
__EXPORT int        param_reset(param_t param);

/**
 * Reset all parameters to their default values.
 *
 * This function also releases the storage used by struct parameters.
 */
__EXPORT void       param_reset_all(void);

/**
 * Reset all parameters to their default values except for excluded parameters.
 *
 * This function also releases the storage used by struct parameters.
 *
 * @param excludes          Array of param names to exclude from resetting. Use a wildcard
 *                          at the end to exclude parameters with a certain prefix.
 * @param num_excludes      The number of excludes provided.
 */
__EXPORT void       param_reset_excludes(const char *excludes[], int num_excludes);

/**
 * Export changed parameters to a file.
 * Note: this method requires a large amount of stack size!
 *
 * @param fd        File descriptor to export to (-1 selects the FLASH storage).
 * @param only_unsaved  Only export changed parameters that have not yet been exported.
 * @return      Zero on success, nonzero on failure.
 */
__EXPORT int        param_export(int fd, bool only_unsaved);

/**
 * Import parameters from a file, discarding any unrecognized parameters.
 *
 * This function merges the imported parameters with the current parameter set.
 *
 * @param fd        File descriptor to import from (-1 selects the FLASH storage).
 * @return      Zero on success, nonzero if an error occurred during import.
 *          Note that in the failure case, parameters may be inconsistent.
 */
__EXPORT int        param_import(int fd);

/**
 * Load parameters from a file.
 *
 * This function resets all parameters to their default values, then loads new
 * values from a file.
 *
 * @param fd        File descriptor to import from (-1 selects the FLASH storage).
 * @return      Zero on success, nonzero if an error occurred during import.
 *          Note that in the failure case, parameters may be inconsistent.
 */
__EXPORT int        param_load(int fd);

/**
 * Apply a function to each parameter.
 *
 * Note that the parameter set is not locked during the traversal. It also does
 * not hold an internal state, so the callback function can block or sleep between
 * parameter callbacks.
 *
 * @param func      The function to invoke for each parameter.
 * @param arg       Argument passed to the function.
 * @param only_changed  If true, the function is only called for parameters whose values have
 *          been changed from the default.
 * @param only_used If true, the function is only called for parameters which have been
 *          used in one of the running applications.
 */
__EXPORT void       param_foreach(void (*func)(void *arg, param_t param), void *arg, bool only_changed, bool only_used);

/**
 * Set the default parameter file name.
 * This has no effect if the FLASH-based storage is enabled.
 *
 * @param filename  Path to the default parameter file.  The file is not required to
 *          exist.
 * @return      Zero on success.
 */
__EXPORT int        param_set_default_file(const char *filename);

/**
 * Get the default parameter file name.
 *
 * @return      The path to the current default parameter file; either as
 *          a result of a call to param_set_default_file, or the
 *          built-in default.
 */
__EXPORT const char *param_get_default_file(void);

/**
 * Save parameters to the default file.
 * Note: this method requires a large amount of stack size!
 *
 * This function saves all parameters with non-default values.
 *
 * @return      Zero on success.
 */
__EXPORT int        param_save_default(void);

/**
 * Load parameters from the default parameter file.
 *
 * @return      Zero on success.
 */
__EXPORT int        param_load_default(void);

/**
 * Generate the hash of all parameters and their values
 *
 * @return      CRC32 hash of all param_ids and values
 */
__EXPORT uint32_t   param_hash_check(void);

/**
 * Print the status of the param system
 *
 */
__EXPORT void   param_print_status(void);

/**
 * Enable/disable the param autosaving.
 * Re-enabling with changed params will not cause an autosave.
 * @param enable true: enable autosaving, false: disable autosaving
 */
__EXPORT void   param_control_autosave(bool enable);

/**
 * Parameter value union.
 */
union param_value_u {
    void        *p;
    int32_t     i;
    float       f;
};

/**
 * Static parameter definition structure.
 *
 * This is normally not used by user code; see the PARAM_DEFINE macros
 * instead.
 */
struct param_info_s {
    const char  *name

// GCC 4.8 and higher don't implement proper alignment of static data on
// 64-bit. This means that the 24-byte param_info_s variables are
// 16 byte aligned by GCC and that messes up the assumption that
// sequential items in the __param segment can be addressed as an array.
// The assumption is that the address of the second parameter is at
// &param[0]+sizeof(param[0]). When compiled with clang it is
// true, with gcc is is not true.
// See https://llvm.org/bugs/show_bug.cgi?format=multiple&id=18006
// The following hack is for GCC >=4.8 only. Clang works fine without
// this.
#ifdef __PX4_POSIX
    __attribute__((aligned(16)));
#else
    ;
#endif
    param_type_t    type;
    uint16_t        volatile_param: 1;
    union param_value_u val;
};

__END_DECLS



#ifdef  __cplusplus
#if 0 // set to 1 to debug param type mismatches
#include <cstdio>
#define CHECK_PARAM_TYPE(param, type) \
    if (param_type(param) != type) { \
        /* use printf() to avoid having to use more includes */ \
        printf("wrong type passed to param_get() for param %s\n", param_name(param)); \
    }
#else
#define CHECK_PARAM_TYPE(param, type)
#endif

// param is a C-interface. This means there is no overloading, and thus no type-safety for param_get().
// So for C++ code we redefine param_get() to inlined overloaded versions, which gives us type-safety
// w/o having to use a different interface
static inline int param_get(param_t param, float *val)
{
    CHECK_PARAM_TYPE(param, PARAM_TYPE_FLOAT);
    return param_get(param, (void *)val);
}
static inline int param_get(param_t param, int32_t *val)
{
    CHECK_PARAM_TYPE(param, PARAM_TYPE_INT32);
    return param_get(param, (void *)val);
}
#undef CHECK_PARAM_TYPE

#endif /* __cplusplus */

#endif