User Type Objects

User type objects are provided to implement special behavior of read and/or write access to an object entry. Several system types are using this mechanism to provide the specified behavior of several pre-defined CANopen object entries.

The implemented access hook functions (called "type functions") are used for any access to the object entry, regardless of the accessing component (CAN network via CAN messages or the application via service functions).

An example user type (called "DemoType") is declared with the following structure.

CO_OBJ_TYPE DemoType = {
    0,             /* runtime reference to object directory    */
    0,             /* 32bit value for usage within type        */
    DemoSize,      /* type function to get object size         */
    DemoCtrl,      /* type function to control type object     */
    DemoRead,      /* type function to read object content     */
    DemoWrite      /* type function to write object content    */
 };

Note: if a new user type don't need to have special behavior on accessing (e.g. get size, control, read data or write data), the corresponding type function can be set to 0 to switch this access to basic behavior.

The following list shows the type function prototypes. The return value of the size type function (e.g. DemoSize()) shall return the size of the user type in bytes. The other type functions shall return CO_ERR.NONE after successful operation. If an error is detected the corresponding error codes must be returned: CO_ERR_TYPE.RD, CO_ERR_TYPE.WR or CO_ERR_TYPE.CTRL.

CPU_INT32U DemoSize (CO_OBJ *obj, CPU_INT32U width);
CPU_INT16S DemoRead (CO_OBJ *obj, void *buf, CPU_INT32U len);
CPU_INT16S DemoWrite(CO_OBJ *obj, void *buf, CPU_INT32U len);
CPU_INT16S DemoCtrl (CO_OBJ *obj, CPU_INT16U func, CPU_INT32U para);

To integrate the user type "DemoType" into the code generation system and keep the object directory definition readable, the following lines should be added within the corresponding header file:

extern CO_OBJ_TYPE DemoType;
 
#define USR_TDEMOTYPE  ((CO_OBJ_TYPE *)&DemoType)

The following diagram shows the internal behavior of read access to the user type object: