stxetx.h

Go to the documentation of this file.

/*! \file stxetx.h \brief STX/ETX Packet Protocol Implementation Library. */
//*****************************************************************************
//
// File Name    : 'stxetx.h'
// Title        : STX/ETX Packet Protocol Implementation Library
// Author       : Pascal Stang - Copyright (C) 2002-2003
// Created      : 10/9/2002
// Revised      : 02/10/2003
// Version      : 0.1
// Target MCU   : any
// Editor Tabs  : 4
//
/// \ingroup general
/// \defgroup stxetx STX/ETX Packet Protocol Library (stxetx.c)
/// \code #include "stxetx.h" \endcode
/// \par Overview
///     This library provides functions needed to transmit and receive STX/ETX
/// packets over any interface which can send and receive bytes.  STX/ETX is a
/// simple packet protocol for serial data streams and offers packetization,
/// type tagging, and checksum protection for user data.  Common uses of STX/ETX
/// might include radio communications were it can improve data reliability over
/// lossy channels.  STX/ETX may also be used effectively anywhere multiple
/// access to the communication medium is required.  The packets can be made
/// to contain destination addresses or routing information as well as data.
///
/// \par STX/ETX Details
///     STX/ETX is a simple packet protocol that can be wrapped around user
/// data for one or more of the following reasons:
///         1. packetization is needed
///             - Using packets can be helpful if your data naturally forms 
///             little "bunches" or if different types of data must be sent
///             over the same channel (a serial cable, for example).  If your
///             data forms "bunches", you can send user data inside STX/ETX
///             packets with a predetermined structure, like an array of A/D
///             conversion results.  If you need a way to tell the receiver
///             what kind of data you're sending, you can use the TYPE field
///             in the STX/ETX packet.
///         2. error checking is needed
///             - STX/ETX packets will add a checksum to your data.  This
///             allows the receiver to verify that data was received correctly
///             and is error-free.  Packets which are corrupted in transmission
///             and fail the the checksum test are automatically discarded.
///             Error checking is especially useful when the data transmission
///             channel is unreliable or noisy (examples: radio, infrared, long
///             cables, etc)
/// 
///     STX/ETX packets have the following structure:
///
///     [STX][status][type][length][user data...][checksum][ETX]
///
///     All fields are 1 byte except for user data which may be 0-255 bytes.
///     Uppercase fields are constant (STX=0x02, ETX=0x03), lowercase fields
///     vary.  The length field is the number of bytes in the user data area.
///     The checksum is the 8-bit sum of all bytes between but not including
///     STX/ETX.
//
// This code is distributed under the GNU Public License
//      which can be found at http://www.gnu.org/licenses/gpl.txt
//
//*****************************************************************************
//@{

#ifndef STXETX_H
#define STXETX_H

#include "buffer.h"

// include project-dependent configuration options
#include "stxetxconf.h"

// constants
// packet markers
#define STX     0x02                // start transmission marker
#define ETX     0x03                // end transmission marker
// packet length parameters
#define STXETX_HEADERLENGTH     4   // number of bytes required for packet header
#define STXETX_TRAILERLENGTH    2   // number of bytes required for packet trailer
// packet field offsets
#define STXETX_STATUSOFFSET     1   // number of bytes from STX to STATUS
#define STXETX_TYPEOFFSET       2   // number of bytes from STX to TYPE
#define STXETX_LENGTHOFFSET     3   // number of bytes from STX to LENGTH
#define STXETX_DATAOFFSET       4   // number of bytes from STX to the data
#define STXETX_CHECKSUMOFFSET   4   // number of bytes from STX+[length] to CHECKSUM
#define STXETX_NOETXSTXCHECKSUM 3   // number of bytes used by STX,ETX,CHECKSUM


// function prototypes

//! Initialize STX/ETX packet protocol library
void stxetxInit(void (*dataout_func)(unsigned char data));

//! Send/Create STX/ETX packet
void stxetxSend(unsigned char status, unsigned char type, unsigned char datalength, unsigned char* dataptr);

//! Process a buffer containing STX/ETX packets
unsigned char stxetxProcess(cBuffer* rxBuffer);

//! Returns the received packet's status
unsigned char stxetxGetRxPacketStatus(void);

//! Returns the received packet's type
unsigned char stxetxGetRxPacketType(void);

//! Returns the received packet's datalength
unsigned char stxetxGetRxPacketDatalength(void);

//! Returns pointer to the received packet's data
unsigned char* stxetxGetRxPacketData(void);


#endif
//@}

---