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@@ -167,3 +167,37 @@ The GPIO test measures how quickly pins can communicate with a processor core; t
 
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+<br><br>
+
+<center>
+<b>Communication</b>
+</center>
+
+<p>
+
+The communication test measures how quickly two nodes can exchange messages; this is relevant for implementing real-time and high data-rate algorithms. In this, the "from" node sends a byte to the "to" node, which adds 1 to it and sends it back. This is repeated many times, and the number of round trips is divided by the total time. Twice that frequency is approximately the byte rate in one direction, and 16 times that frequency is approximately the bit rate in one direction.
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+<center>
+<table border="1" style="text-align:center">
+
+<tr>
+<th>frequency (MHz)</th>
+<th>from</th>
+<th>link</th>
+<th>to</th>
+<th>date</th>
+</tr>
+
+<tr>
+<td>0.007</td>
+<td><a href=comm/pySerial/ring.pySerial.py>i7-8700T, Python, pySerial</a></td>
+<td>USB 2.1</td>
+<td><a href=comm/SerialUSB/ring.SerialUSB.ino>ATSAMD11C, Arduino, SerialUSB</a></td>
+<td>March 2021</td>
+</tr>
+
+</table>
+</center>
+
+<br><br>