title: how to deal with the serial port in android mobile?
body: <p>actually I know no thing about serial port. but I see an example of sending it an at-command:</p>
  
  <pre><code>echo -e "AT" &gt; /dev/smd0
  </code></pre>
  
  <p>What is /dev/smd0 and why they sometimes replace it with /dev/ttyS0. </p>