Write example
=============

The following example shows how data can be written from a CAN object.  The
driver should already having been opened and the CAN object should have been
defined as a write-object::

  int write_data(int driver_handle, int object_id, int port,
                  unsigned long data)
    { /* writes 4 bytes from the CAN object with the id <object_id> */
      vcan_request     vreq; /* a variable of this type is needed for 
                                read- and write commands */
                             
      vreq.tag             = VCAN_WRITE;/* the command is a WRITE */
      vreq.message.id      = object_id; /* the CAN object-id */
      vreq.message.datasize= 4;         /* an "unsigned long" has 4 bytes,
                                           "sizeof(unsigned long)" could (in 
                                           this example) also be used */
      vreq.message.port    = port;      /* No. of the CAN port that is 
                                           used */
      
      /* now copy the data to the data-area of the request-structure, which 
         is vreq.message.data and is an array of 8 bytes. In this example, 
         however, only 4 bytes are written to the object. */
      memcpy(vreq.message.data, &(data), 4);
      
      write(driver_handle, (char *)(&vreq), sizeof(vreq));
      
      if (vreq.message.stat != VCAN_OK)
        /* a STATUS was returned, e.g. VCAN_TX_ERR (timeout) */
        { if (vreq.message.stat==VCAN_TX_ERR)
            { printf("an error occured, error-code: %d",
                     vreq.message.errcode);
              return(-1);
            };
          /* there can be other status-values e.g.  VCAN_ACCESS_ERR,
             in this example we return always -1 when the status is not 
             VCAN_OK */
          return(-1);
        };
      return(0);
    }