AP_Param: added convert_parameter_width()

this allows for easy conversion of the width of a parameter without
changing indexes

libraries/AP_Param/AP_Param.cpp

@@ -1832,6 +1832,65 @@ void AP_Param::convert_parent_class(uint8_t param_key, void *object_pointer,
     }
 }
 
+/*
+ convert width of a parameter, allowing update to wider scalar values
+ without changing the parameter indexes
+*/
+bool AP_Param::convert_parameter_width(ap_var_type old_ptype)
+{
+    if (configured_in_storage()) {
+        // already converted or set by the user
+        return false;
+    }
+
+    uint32_t group_element = 0;
+    const struct GroupInfo *ginfo;
+    struct GroupNesting group_nesting {};
+    uint8_t idx;
+    const struct AP_Param::Info *info = find_var_info(&group_element, ginfo, group_nesting, &idx);
+
+    if (info == nullptr) {
+        return false;
+    }
+
+    // remember the type
+    ap_var_type new_ptype;
+    if (ginfo != nullptr) {
+        new_ptype = (ap_var_type)ginfo->type;
+    } else {
+        new_ptype = (ap_var_type)info->type;
+    }
+    
+    // create the header we will use to scan for the variable
+    struct Param_header phdr;
+    phdr.type = old_ptype;
+    set_key(phdr, info->key);
+    phdr.group_element = group_element;
+
+    // scan EEPROM to find the right location
+    uint16_t pofs;
+    if (!scan(&phdr, &pofs)) {
+        // it isn't in storage
+        return false;
+    }
+
+    // load the old value from EEPROM
+    uint8_t old_value[type_size(old_ptype)];
+    _storage.read_block(old_value, pofs+sizeof(phdr), sizeof(old_value));
+    
+    AP_Param *old_ap = (AP_Param *)&old_value[0];
+
+    // going via float is safe as the only time we would be converting
+    // from AP_Int32 is when converting to float
+    float old_float_value = old_ap->cast_to_float(old_ptype);
+    set_value(new_ptype, this, old_float_value);
+
+    // force save as the new type
+    save(true);
+
+    return true;
+}
+
 
 /*
   set a parameter to a float value

libraries/AP_Param/AP_Param.h

@@ -389,6 +389,13 @@ public:
     // convert old vehicle parameters to new object parameters
     static void         convert_old_parameters(const struct ConversionInfo *conversion_table, uint8_t table_size, uint8_t flags=0);
 
+    /*
+      convert width of a parameter, allowing update to wider scalar
+      values without changing the parameter indexes. This will return
+      true if the parameter was converted from an old parameter value
+    */
+    bool convert_parameter_width(ap_var_type old_ptype);
+    
     // convert a single parameter with scaling
     enum {
         CONVERT_FLAG_REVERSE=1, // handle _REV -> _REVERSED conversion