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8 <h1>stxetx.c</h1><a href="stxetx_8c.html">Go to the documentation of this file.</a><div class="fragment"><pre class="fragment">00001 <span class="comment">/*! \file stxetx.c \brief STX/ETX Packet Protocol Implementation Library. */</span>
9 00002 <span class="comment">//*****************************************************************************</span>
10 00003 <span class="comment">//</span>
11 00004 <span class="comment">// File Name : 'stxetx.c'</span>
12 00005 <span class="comment">// Title : STX/ETX Packet Protocol Implementation Library</span>
13 00006 <span class="comment">// Author : Pascal Stang - Copyright (C) 2002</span>
14 00007 <span class="comment">// Created : 10/9/2002</span>
15 00008 <span class="comment">// Revised : 6/30/2003</span>
16 00009 <span class="comment">// Version : 0.1</span>
17 00010 <span class="comment">// Target MCU : any</span>
18 00011 <span class="comment">// Editor Tabs : 4</span>
19 00012 <span class="comment">//</span>
20 00013 <span class="comment">// Description : This library provides a set of functions needed to send and</span>
21 00014 <span class="comment">// receive STX/ETX packets. STX/ETX is a simple packet protocol that can</span>
22 00015 <span class="comment">// be wrapped around user data for one or more of the following reasons:</span>
23 00016 <span class="comment">//</span>
24 00017 <span class="comment">// 1. packetization is needed</span>
25 00018 <span class="comment">// - Using packets can be helpful if your data naturally forms </span>
26 00019 <span class="comment">// little "bunches" or if different types of data must be sent</span>
27 00020 <span class="comment">// over the same channel (a serial cable, for example). If your</span>
28 00021 <span class="comment">// data forms "bunches", you can send user data inside STX/ETX</span>
29 00022 <span class="comment">// packets with a predetermined structure, like an array of A/D</span>
30 00023 <span class="comment">// conversion results. If you need a way to tell the receiver</span>
31 00024 <span class="comment">// what kind of data you're sending, you can use the TYPE field</span>
32 00025 <span class="comment">// in the STX/ETX packet.</span>
33 00026 <span class="comment">// 2. error checking is needed</span>
34 00027 <span class="comment">// - STX/ETX packets will add a checksum to your data. This</span>
35 00028 <span class="comment">// allows the receiver to verify that data was received correctly</span>
36 00029 <span class="comment">// and is error-free. Packets which are corrupted in transmission</span>
37 00030 <span class="comment">// and fail the the checksum test are automatically discarded.</span>
38 00031 <span class="comment">// Error checking is especially useful when the data transmission</span>
39 00032 <span class="comment">// channel is unreliable or noisy (examples: radio, infrared, long</span>
40 00033 <span class="comment">// cables, etc)</span>
41 00034 <span class="comment">// </span>
42 00035 <span class="comment">// STX/ETX packets have the following structure:</span>
43 00036 <span class="comment">//</span>
44 00037 <span class="comment">// [STX][status][type][length][user data...][checksum][ETX]</span>
45 00038 <span class="comment">//</span>
46 00039 <span class="comment">// All fields are 1 byte except for user data which may be 0-255 bytes.</span>
47 00040 <span class="comment">// Uppercase fields are constant (STX=0x02, ETX=0x03), lowercase fields</span>
48 00041 <span class="comment">// vary. The length field is the number of bytes in the user data area.</span>
49 00042 <span class="comment">// The checksum is the 8-bit sum of all bytes between but not including</span>
50 00043 <span class="comment">// STX/ETX.</span>
51 00044 <span class="comment">//</span>
52 00045 <span class="comment">// This code is distributed under the GNU Public License</span>
53 00046 <span class="comment">// which can be found at http://www.gnu.org/licenses/gpl.txt</span>
54 00047 <span class="comment">//</span>
55 00048 <span class="comment">//*****************************************************************************</span>
56 00049
57 00050 <span class="preprocessor">#include "<a class="code" href="global_8h.html">global.h</a>"</span>
58 00051 <span class="preprocessor">#include "<a class="code" href="stxetx_8h.html">stxetx.h</a>"</span>
59 00052 <span class="comment">//#include "rprintf.h"</span>
60 00053
61 00054 <span class="comment">// function pointer to data output routine</span>
62 00055 <span class="keyword">static</span> void (*stxetxDataOut)(<span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> data);
63 00056
64 00057 <span class="comment">// received packet data buffer</span>
65 00058 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> stxetxRxPacket[STXETX_MAXRXPACKETSIZE];
66 00059
67 00060 <span class="comment">// functions</span>
68 00061
69 00062
70 00063 <span class="comment">// Initialize STX/ETX packet protocol library</span>
71 <a name="l00064"></a><a class="code" href="group__stxetx.html#ga0">00064</a> <span class="keywordtype">void</span> <a class="code" href="group__stxetx.html#ga0">stxetxInit</a>(<span class="keywordtype">void</span> (*dataout_func)(<span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> data))
72 00065 {
73 00066 stxetxDataOut = dataout_func;
74 00067 }
75 00068
76 00069 <span class="comment">// Send/Create STX/ETX packet</span>
77 <a name="l00070"></a><a class="code" href="group__stxetx.html#ga1">00070</a> <span class="keywordtype">void</span> <a class="code" href="group__stxetx.html#ga1">stxetxSend</a>(<span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> status, <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> type, <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> datalength, <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span>* dataptr)
78 00071 {
79 00072 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> checksum = 0;
80 00073 <span class="keywordtype">unsigned</span> <span class="keywordtype">short</span> i;
81 00074
82 00075 <span class="comment">// write packet header</span>
83 00076 stxetxDataOut(STX);
84 00077 stxetxDataOut(status);
85 00078 stxetxDataOut(type);
86 00079 stxetxDataOut(datalength);
87 00080 <span class="comment">// update checksum</span>
88 00081 checksum += status + type + datalength;
89 00082 <span class="comment">// copy data into packet</span>
90 00083 <span class="keywordflow">for</span>(i = 0; i &lt; datalength; i++)
91 00084 {
92 00085 stxetxDataOut(*dataptr);
93 00086 checksum += *dataptr;
94 00087 dataptr++;
95 00088 }
96 00089 <span class="comment">// write packet trailer</span>
97 00090 stxetxDataOut(checksum);
98 00091 stxetxDataOut(ETX);
99 00092 }
100 00093
101 00094 <span class="comment">// process buffer containing STX/ETX packets</span>
102 <a name="l00095"></a><a class="code" href="group__stxetx.html#ga2">00095</a> <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> <a class="code" href="group__stxetx.html#ga2">stxetxProcess</a>(<a class="code" href="structstruct__cBuffer.html">cBuffer</a>* rxBuffer)
103 00096 {
104 00097 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> foundpacket = FALSE;
105 00098 <span class="keywordtype">unsigned</span> <span class="keywordtype">short</span> i;
106 00099 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> length, checksum;
107 00100 <span class="comment">//unsigned char type;</span>
108 00101
109 00102 <span class="comment">// process the buffer</span>
110 00103 <span class="comment">// go through buffer looking for packets</span>
111 00104 <span class="comment">// the STX must be located at least STXETX_HEADERLENGTH+STXETX_TRAILERLENGTH from end</span>
112 00105 <span class="comment">// otherwise we must not have a complete packet</span>
113 00106 <span class="keywordflow">while</span>( rxBuffer-&gt;<a class="code" href="structstruct__cBuffer.html#o2">datalength</a> &gt;= ((u16)STXETX_HEADERLENGTH+(u16)STXETX_TRAILERLENGTH) )
114 00107 {
115 00108 <span class="comment">// look for a potential start of packet</span>
116 00109 <span class="keywordflow">if</span>(<a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, 0) == STX)
117 00110 {
118 00111 <span class="comment">// if this is a start, then get the length</span>
119 00112 length = <a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, STXETX_LENGTHOFFSET);
120 00113
121 00114 <span class="comment">// now we must have at least STXETX_HEADERLENGTH+length+STXETX_TRAILERLENGTH in buffer to continue</span>
122 00115 <span class="keywordflow">if</span>(rxBuffer-&gt;<a class="code" href="structstruct__cBuffer.html#o2">datalength</a> &gt;= ((u16)STXETX_HEADERLENGTH+length+(u16)STXETX_TRAILERLENGTH))
123 00116 {
124 00117 <span class="comment">// check to see if ETX is in the right position</span>
125 00118 <span class="keywordflow">if</span>(<a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, STXETX_HEADERLENGTH+length+STXETX_TRAILERLENGTH-1) == ETX)
126 00119 {
127 00120 <span class="comment">// found potential packet</span>
128 00121 <span class="comment">// test checksum</span>
129 00122 checksum = 0;
130 00123 <span class="comment">// sum data between STX and ETX, not including checksum itself</span>
131 00124 <span class="comment">// (u16) casting needed to avoid unsigned/signed mismatch</span>
132 00125 <span class="keywordflow">for</span>(i = 0; i&lt;((u16)STXETX_HEADERLENGTH+length+(u16)STXETX_TRAILERLENGTH-(u16)STXETX_NOETXSTXCHECKSUM); i++)
133 00126 {
134 00127 checksum += <a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, i+STXETX_STATUSOFFSET);
135 00128 }
136 00129 <span class="comment">// compare checksums</span>
137 00130 <span class="keywordflow">if</span>(checksum == <a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, STXETX_CHECKSUMOFFSET+length))
138 00131 {
139 00132 <span class="comment">//we have a packet!</span>
140 00133 foundpacket = TRUE;
141 00134
142 00135 <span class="comment">// copy data to buffer</span>
143 00136 <span class="comment">// (don't copy STX, ETX, or CHECKSUM)</span>
144 00137 <span class="keywordflow">for</span>(i = 0; i &lt; ((u16)STXETX_HEADERLENGTH+length-1); i++)
145 00138 {
146 00139 stxetxRxPacket[i] = <a class="code" href="group__buffer.html#ga4">bufferGetAtIndex</a>(rxBuffer, i+1);
147 00140 }
148 00141
149 00142 <span class="comment">// debug</span>
150 00143 <span class="comment">//rprintf("STXETX Received packet type: 0x%x\n", bufferGetAtIndex(rxBuffer, STXETX_TYPEOFFSET));</span>
151 00144
152 00145 <span class="comment">// dump this packet from the</span>
153 00146 <a class="code" href="group__buffer.html#ga3">bufferDumpFromFront</a>(rxBuffer, STXETX_HEADERLENGTH+length+STXETX_TRAILERLENGTH);
154 00147
155 00148 <span class="comment">// done with this processing session</span>
156 00149 <span class="keywordflow">break</span>;
157 00150 }
158 00151 <span class="keywordflow">else</span>
159 00152 {
160 00153 <span class="comment">// checksum bad</span>
161 00154 <span class="comment">//rprintf("STXETX Received packet with bad checksum\r\n");</span>
162 00155 <span class="comment">// for now, we dump these</span>
163 00156 <span class="comment">// dump this STX</span>
164 00157 <a class="code" href="group__buffer.html#ga2">bufferGetFromFront</a>(rxBuffer);
165 00158 }
166 00159 }
167 00160 <span class="keywordflow">else</span>
168 00161 {
169 00162 <span class="comment">// no ETX or ETX in wrong position</span>
170 00163 <span class="comment">// dump this STX</span>
171 00164 <a class="code" href="group__buffer.html#ga2">bufferGetFromFront</a>(rxBuffer);
172 00165 }
173 00166 }
174 00167 <span class="keywordflow">else</span>
175 00168 {
176 00169 <span class="comment">// not enough data in buffer to decode pending packet</span>
177 00170 <span class="comment">// wait until next time</span>
178 00171 <span class="keywordflow">break</span>;
179 00172 }
180 00173 }
181 00174 <span class="keywordflow">else</span>
182 00175 {
183 00176 <span class="comment">// this is not a start, dump it</span>
184 00177 <a class="code" href="group__buffer.html#ga2">bufferGetFromFront</a>(rxBuffer);
185 00178 }
186 00179 }
187 00180
188 00181 <span class="comment">// check if receive buffer is full with no packets decoding</span>
189 00182 <span class="comment">// (ie. deadlocked on garbage data or packet that exceeds buffer size)</span>
190 00183 <span class="keywordflow">if</span>(!<a class="code" href="group__buffer.html#ga6">bufferIsNotFull</a>(rxBuffer))
191 00184 {
192 00185 <span class="comment">// dump receive buffer contents to relieve deadlock</span>
193 00186 <a class="code" href="group__buffer.html#ga7">bufferFlush</a>(rxBuffer);
194 00187 }
195 00188
196 00189 <span class="keywordflow">return</span> foundpacket;
197 00190 }
198 00191
199 <a name="l00192"></a><a class="code" href="group__stxetx.html#ga3">00192</a> <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> <a class="code" href="group__stxetx.html#ga3">stxetxGetRxPacketStatus</a>(<span class="keywordtype">void</span>)
200 00193 {
201 00194 <span class="comment">// return the packet's status</span>
202 00195 <span class="comment">// (subtract 1 from the offset because the STX has already been discarded)</span>
203 00196 <span class="keywordflow">return</span> stxetxRxPacket[STXETX_STATUSOFFSET-1];
204 00197 }
205 00198
206 <a name="l00199"></a><a class="code" href="group__stxetx.html#ga4">00199</a> <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> <a class="code" href="group__stxetx.html#ga4">stxetxGetRxPacketType</a>(<span class="keywordtype">void</span>)
207 00200 {
208 00201 <span class="comment">// return the packet's type</span>
209 00202 <span class="comment">// (subtract 1 from the offset because the STX has already been discarded)</span>
210 00203 <span class="keywordflow">return</span> stxetxRxPacket[STXETX_TYPEOFFSET-1];
211 00204 }
212 00205
213 <a name="l00206"></a><a class="code" href="group__stxetx.html#ga5">00206</a> <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> <a class="code" href="group__stxetx.html#ga5">stxetxGetRxPacketDatalength</a>(<span class="keywordtype">void</span>)
214 00207 {
215 00208 <span class="comment">// return the packet's datalength</span>
216 00209 <span class="comment">// (subtract 1 from the offset because the STX has already been discarded)</span>
217 00210 <span class="keywordflow">return</span> stxetxRxPacket[STXETX_LENGTHOFFSET-1];
218 00211 }
219 00212
220 <a name="l00213"></a><a class="code" href="group__stxetx.html#ga6">00213</a> <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span>* <a class="code" href="group__stxetx.html#ga6">stxetxGetRxPacketData</a>(<span class="keywordtype">void</span>)
221 00214 {
222 00215 <span class="comment">// return a pointer to the packet's data payload</span>
223 00216 <span class="comment">// (subtract 1 from the offset because the STX has already been discarded)</span>
224 00217 <span class="keywordflow">return</span> stxetxRxPacket+STXETX_DATAOFFSET-1;
225 00218 }
226 </pre></div><hr size="1"><address style="align: right;"><small>Generated on Sun Oct 29 03:41:07 2006 for Procyon AVRlib by&nbsp;
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228 <img src="doxygen.png" alt="doxygen" align="middle" border="0"></a> 1.4.2 </small></address>
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