Real-Time Workshop

Guidelines for Implementing the Transport Layer

Requirements

• ext_svr.c and updown.c use malloc to allocate buffers in target memory for messages, data collection, and other purposes. If your target uses some other memory allocation scheme, you must modify these modules appropriately.
• The target is assumed to support both int32_T and uint32_T data types.

Modifying ext_transport

The function prototypes in ext_transport.h define the calling interface for the host (client) side transport layer functions. The implementation is in ext_transport.c.

To implement the host side of your transport layer:

• Replace the functions in the "Visible Functions" section of ext_transport.c with functions that call your low-level communications primitives. The visible functions are called from other external mode modules such as ext_comm.c. You must implement all the functions defined in ext_transport.h. Your implementations must conform to the prototypes defined in ext_transport.h.
• Supply a definition for the UserData structure in ext_transport.c. This structure is required. If UserData is not necessary for your external mode implementation, define a UserData structure with one dummy field.
• Replace the functions in ext_transport_share.h with functions that call your low-level communications primitives, or remove these functions. Functions defined in ext_transport_share.h are common to the host and target, and are not part of the public interface to the transport layer.
• Rebuild the ext_comm MEX-file, using the MATLAB mex command. This requires a compiler supported by the MATLAB API. See External Interfaces/API in the MATLAB online documentation for more information on the mex command. The following table lists the form of the commands to build the standard ext_comm module on PC and UNIX platforms.
  
  

  Table 14-5: Commands to Rebuild ext_comm MEX-Files

  Platform	Commands
  PC	cd matlabroot\toolbox\rtw mex matlabroot\rtw\ext_mode\ext_comm.c     matlabroot\rtw\ext_mode\ext_convert.c     matlabroot\rtw\ext_mode\ext_transport.c     -Imatlab\rtw\c\src -DWIN32     compiler_library_path\wsock32.lib
  UNIX	cd matlabroot/toolbox/rtw mex matlabroot/rtw/ext_mode/ext_comm.c     matlabroot/rtw/ext_mode/ext_convert.c     matlabroot/rtw/ext_mode/ext_transport.c     -Imatlab/rtw/c/src

The ext_transport and ext_transport_share source code modules are fully commented. See these files for further details.

Guidelines for Modifying ext_svr_transport

The function prototypes in ext_svr_transport.h define the calling interface for the target (server) side transport layer functions. The implementation is in ext_svr_transport.c.

To implement the target side of your transport layer:

• Replace the functions in ext_svr_transport.c with functions that call your low-level communications primitives. These are the functions called from other target modules such as the main program. You must implement all the functions defined in ext_svr_transport.h. Your implementations must conform to the prototypes defined in ext_svr_transport.h.
• Supply a definition for the ExtUserData structure in ext_svr_transport.c. This structure is required. If ExtUserData is not necessary for your external mode implementation, define an ExtUserData structure with one dummy field.
• Define the EXT_BLOCKING conditional in ext_svr_transport.c as needed:
• Define EXT_BLOCKING as 0 to poll for a connection to the host (appropriate for single-threaded applications).
• Define EXT_BLOCKING as 1 in multi-threaded applications where tasks are able to block for a connection to the host without blocking the entire program.

• See also the comments on EXT_BLOCKING in ext_svr_transport.c.

The ext_svr_transport source code modules are fully commented. See these files for further details.

External Mode Source Files

Combining Multiple Models