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<!DOCTYPE <h <t <link </head><body> <!-- <div <h 00002 00003 00004 00005 00006 00007 00008 00009 00010 00011 00012 00013 00014 00015 00016 00017 00018 00019 00020 00021 00022 00023 00024 00025 00026 00027 00028 00029 00030 00031 00032 00033 00034 00035 00036 00037 00038 00039 00040 00041 00042 00043 00044 00045 00046 00047 00048 00049 00050 00051 00052 00053 00054 00055 00056 00057 00058 00059 00060 00061 00062 00063 <a 00065 { 00066 00067 } 00068 00069 <a 00071 { 00072 00073 00074 00075 00076 00077 00078 00079 00080 00081 00082 00083 00084 { 00085 00086 00087 dataptr++; 00088 } 00089 00090 00091 00092 } 00093 00094 <a 00096 { 00097 00098 00099 00100 00101 00102 00103 00104 00105 00106 00107 { 00108 00109 00110 { 00111 00112 00113 00114 00115 00116 { 00117 00118 00119 { 00120 00121 00122 00123 00124 00125 00126 00127 00128 00129 00130 00131 00132 00133 00134 00135 00136 00137 00138 00139 00140 00141 00142 00143 00144 00145 00146 00147 00148 00149 00150 00151 00152 00153 00154 00155 00156 00157 00158 00159 } 00160 00161 { 00162 00163 00164 00165 } 00166 } 00167 00168 { 00169 00170 00171 00172 } 00173 } 00174 00175 { 00176 00177 00178 } 00179 } 00180 00181 00182 00183 00184 { 00185 00186 00187 } 00188 00189 00190 } 00191 <a 00193 { 00194 00195 00196 00197 } 00198 <a 00200 { 00201 00202 00203 00204 } 00205 <a 00207 { 00208 00209 00210 00211 } 00212 <a 00214 { 00215 00216 00217 00218 } </ <a <img </body> </html>

HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> tml><head><meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"> itle>Procyon AVRlib: stxetx.c Source File</title> href="dox.css" rel="stylesheet" type="text/css"> Generated by Doxygen 1.4.2 --> class="qindex"><a class="qindex" href="main.html">Main Page</a> | <a class="qindex" href="modules.html">Modules</a> | <a class="qindex" href="annotated.html">Data Structures</a> | <a class="qindex" href="dirs.html">Directories</a> | <a class="qindex" href="files.html">File List</a> | <a class="qindex" href="functions.html">Data Fields</a> | <a class="qindex" href="globals.html">Globals</a> | <a class="qindex" href="pages.html">Related Pages</a></div> 1>stxetx.c</h1><a href="stxetx_8c.html">Go to the documentation of this file.</a><div class="fragment"><pre class="fragment">00001 /*! \file stxetx.c \brief STX/ETX Packet Protocol Implementation Library. */ //***************************************************************************** // // File Name : 'stxetx.c' // Title : STX/ETX Packet Protocol Implementation Library // Author : Pascal Stang - Copyright (C) 2002 // Created : 10/9/2002 // Revised : 6/30/2003 // Version : 0.1 // Target MCU : any // Editor Tabs : 4 // // Description : This library provides a set of functions needed to send and // receive STX/ETX packets. 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 // //***************************************************************************** #include "<a class="code" href="global_8h.html">global.h</a>" #include "<a class="code" href="stxetx_8h.html">stxetx.h</a>" //#include "rprintf.h" // function pointer to data output routine static void (*stxetxDataOut)(unsigned char data); // received packet data buffer unsigned char stxetxRxPacket[STXETX_MAXRXPACKETSIZE]; // functions // Initialize STX/ETX packet protocol library name="l00064"></a><a class="code" href="group__stxetx.html#ga0">00064</a> void <a class="code" href="group__stxetx.html#ga0">stxetxInit</a>(void (*dataout_func)(unsigned char data)) stxetxDataOut = dataout_func; // Send/Create STX/ETX packet name="l00070"></a><a class="code" href="group__stxetx.html#ga1">00070</a> void <a class="code" href="group__stxetx.html#ga1">stxetxSend</a>(unsigned char status, unsigned char type, unsigned char datalength, unsigned char* dataptr) unsigned char checksum = 0; unsigned short i; // write packet header stxetxDataOut(STX); stxetxDataOut(status); stxetxDataOut(type); stxetxDataOut(datalength); // update checksum checksum += status + type + datalength; // copy data into packet for(i = 0; i < datalength; i++) stxetxDataOut(*dataptr); checksum += *dataptr; // write packet trailer stxetxDataOut(checksum); stxetxDataOut(ETX); // process buffer containing STX/ETX packets name="l00095"></a><a class="code" href="group__stxetx.html#ga2">00095</a> unsigned char <a class="code" href="group__stxetx.html#ga2">stxetxProcess</a>(<a class="code" href="structstruct__cBuffer.html">cBuffer</a>* rxBuffer) unsigned char foundpacket = FALSE; unsigned short i; unsigned char length, checksum; //unsigned char type; // process the buffer // go through buffer looking for packets // the STX must be located at least STXETX_HEADERLENGTH+STXETX_TRAILERLENGTH from end // otherwise we must not have a complete packet while( rxBuffer-><a class="code" href="structstruct__cBuffer.html#o2">datalength</a> >= ((u16)STXETX_HEADERLENGTH+(u16)STXETX_TRAILERLENGTH) ) // look for a potential start of packet if(<a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, 0) == STX) // if this is a start, then get the length length = <a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, STXETX_LENGTHOFFSET); // now we must have at least STXETX_HEADERLENGTH+length+STXETX_TRAILERLENGTH in buffer to continue if(rxBuffer-><a class="code" href="structstruct__cBuffer.html#o2">datalength</a> >= ((u16)STXETX_HEADERLENGTH+length+(u16)STXETX_TRAILERLENGTH)) // check to see if ETX is in the right position if(<a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, STXETX_HEADERLENGTH+length+STXETX_TRAILERLENGTH-1) == ETX) // found potential packet // test checksum checksum = 0; // sum data between STX and ETX, not including checksum itself // (u16) casting needed to avoid unsigned/signed mismatch for(i = 0; i<((u16)STXETX_HEADERLENGTH+length+(u16)STXETX_TRAILERLENGTH-(u16)STXETX_NOETXSTXCHECKSUM); i++) { checksum += <a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, i+STXETX_STATUSOFFSET); } // compare checksums if(checksum == <a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, STXETX_CHECKSUMOFFSET+length)) { //we have a packet! foundpacket = TRUE; // copy data to buffer // (don't copy STX, ETX, or CHECKSUM) for(i = 0; i < ((u16)STXETX_HEADERLENGTH+length-1); i++) { stxetxRxPacket[i] = <a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, i+1); } // debug //rprintf("STXETX Received packet type: 0x%x\n", bufferGetAtIndex(rxBuffer, STXETX_TYPEOFFSET)); // dump this packet from the <a class="code" href="group__buffer.html#ga3">bufferDumpFromFront</a>(rxBuffer, STXETX_HEADERLENGTH+length+STXETX_TRAILERLENGTH); // done with this processing session break; } else { // checksum bad //rprintf("STXETX Received packet with bad checksum\r\n"); // for now, we dump these // dump this STX <a class="code" href="group__buffer.html#ga2">bufferGetFromFront</a>(rxBuffer); } else // no ETX or ETX in wrong position // dump this STX <a class="code" href="group__buffer.html#ga2">bufferGetFromFront</a>(rxBuffer); else // not enough data in buffer to decode pending packet // wait until next time break; else // this is not a start, dump it <a class="code" href="group__buffer.html#ga2">bufferGetFromFront</a>(rxBuffer); // check if receive buffer is full with no packets decoding // (ie. deadlocked on garbage data or packet that exceeds buffer size) if(!<a class="code" href="group__buffer.html#ga6">bufferIsNotFull</a>(rxBuffer)) // dump receive buffer contents to relieve deadlock <a class="code" href="group__buffer.html#ga7">bufferFlush</a>(rxBuffer); return foundpacket; name="l00192"></a><a class="code" href="group__stxetx.html#ga3">00192</a> unsigned char <a class="code" href="group__stxetx.html#ga3">stxetxGetRxPacketStatus</a>(void) // return the packet's status // (subtract 1 from the offset because the STX has already been discarded) return stxetxRxPacket[STXETX_STATUSOFFSET-1]; name="l00199"></a><a class="code" href="group__stxetx.html#ga4">00199</a> unsigned char <a class="code" href="group__stxetx.html#ga4">stxetxGetRxPacketType</a>(void) // return the packet's type // (subtract 1 from the offset because the STX has already been discarded) return stxetxRxPacket[STXETX_TYPEOFFSET-1]; name="l00206"></a><a class="code" href="group__stxetx.html#ga5">00206</a> unsigned char <a class="code" href="group__stxetx.html#ga5">stxetxGetRxPacketDatalength</a>(void) // return the packet's datalength // (subtract 1 from the offset because the STX has already been discarded) return stxetxRxPacket[STXETX_LENGTHOFFSET-1]; name="l00213"></a><a class="code" href="group__stxetx.html#ga6">00213</a> unsigned char* <a class="code" href="group__stxetx.html#ga6">stxetxGetRxPacketData</a>(void) // return a pointer to the packet's data payload // (subtract 1 from the offset because the STX has already been discarded) return stxetxRxPacket+STXETX_DATAOFFSET-1; pre></div><hr size="1"><address style="align: right;">Generated on Sun Oct 29 03:41:07 2006 for Procyon AVRlib by  href="http://www.doxygen.org/index.html"> src="doxygen.png" alt="doxygen" align="middle" border="0"></a> 1.4.2 </address>

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