Allocates an Rx message object. 
- Parameters
- 
  
    | inst_ptr | Reference to an internal UNICENS handler |  | buffer_size | The size in bytes of the received Rx message. Valid values: 6..72. |  
 
- Returns
- The Rx message object or NULLif no message object is available. In the latter case the low-level driver can wait until Ucs_Lld_RxMsgAvailableCb_t() is invoked. The low-level driver is allowed to pre-allocate Rx messages with the maximum size of 72 bytes. After writing received data into Ucs_Lld_RxMsg_t::data_ptr the low-level driver must set Ucs_Lld_RxMsg_t::data_size to the actual message size.
- Warning
- The function will also return NULLif the requestedbuffer_sizeexceeds the valid range. In such a case the UNICENS cannot guarantee that Ucs_Lld_RxMsgAvailableCb_t() is called as expected. Received messages exceeding the valid range must be discarded by the LLD.