representations

When electronic devices are communicating with each other, they need a common data representation to serialize and deserialize data. This libraray defines a set of messages as c-structs in a number of header files. Each distinct message is identified by the id contained in the first byte of a received binary blob, which is choosen before compile-time in names.c.

The provided information is used to generate three files:

• A vhdl-mapping for PacketId -> Symbol, put into the folder "vhdl", located inside this repository
• A header for mapping packet id to symbol, put inside the build-tree. Use pkg-config to retrieve the needed compiler-flags for in-source builds.
• A common yaml-file containing all information from names.c in an easily readable format

Limit usage of advanced C language feature. Unions and bitfields are not a good idea.

Adding new types

Iff you really need a new package format.

• Declare your new struct in a header here

  #ifndef REPRESENTATIONS_MYTYPE_H
  #define REPRESENTATIONS_MYTYPE_H
  
  #include "include/Representation.h"
  
  struct MyType {
      /** inheritance the c-way: */
      struct Representation mBase;
      /** your actual payload */
      float value;
  } __attribute__((packed));
  
  #ifdef __cplusplus
  namespace representations {
      struct Acceleration : public ::Acceleration {} __attribute__((packed));
  }
  #endif
  
  #endif

• modify names.c to augment the database for later stages:

  diff --git a/src/names.c b/src/names.c
  index 931568b..d9c0d59 100644
  --- a/src/names.c
  +++ b/src/names.c
  @@ -145,6 +145,8 @@ static const struct RepresentationsNamesEntry representationsDatabase[] =
       
       {202, "ForwardDynamicsMessage", FIXED_PACKET_SIZE, "ForwardDynamicsMessage.h"},
       {203, "BackwardDynamicsMessage", FIXED_PACKET_SIZE, "BackwardDynamicsMessage.h"},
  +
  +    {230, "MyType", FIXED_PACKET_SIZE, "MyType.h"},
       
       // end-of-list
       {0,0,0,0}

represupport

Some packet types have common behaviour associated, so a set of helper functions can be provided to handle these. This is rather advanced, and intended to be combined with the "ndlcom" communication library. The packages in questions:

• Ping
• DebugMessage
• RegisterValueWrite, RegisterValueQuery, RegisterDescriptionQuery
• STOP, RESUME, RESET
• RoutingTable (Note: no FPGA implementation yet)

History

Developed at DKFI RIC Bremen during the iStruct and SeeGrip projects