NSH dd command test with block devices

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@1242 42af7a65-404d-4744-a932-0658087f49c3

Documentation/NuttShell.html

@@ -754,14 +754,50 @@ dd if=<infile> of=<outfile> [bs=<sectsize>] [count=<sectors
 </pre></ul>
 <p>
   <b>Synopsis</b>.
-  Copy blocks from &lt;infile&gt; to &lt;outfile&gt;.  As an example:
+  Copy blocks from &lt;infile&gt; to &lt;outfile&gt;.
+  &lt;infile&gt; or &lt;outfile&gt; may be the path to a standard file, a character device, or a block device.
+  Examples follow:
+</p>
+<ol>
+  <li>
+    Read from character device, write to regular file.
+    This will create a new file of the specified size filled with zero.
 <ul><pre>
+nsh&gt; ls -l /dev
+/dev:
+ crw-rw-rw-       0 zero
 nsh&gt; dd if=/dev/zero of=/tmp/zeros bs=64 count=16
 nsh&gt; ls -l /tmp
 /tmp:
  -rw-rw-rw-    1024 ZEROS
 </pre></ul>
-</p>
+  </li>
+  <li>
+    Read from character device, write to block device.
+    This will fill the entire block device with zeros.
+  </li>
+<ul><pre>
+nsh&gt; ls -l /dev
+/dev:
+ brw-rw-rw-       0 ram0
+ crw-rw-rw-       0 zero
+nsh&gt; dd if=/dev/zero of=/dev/ram0
+</pre></ul>
+  </li>
+  <li>
+    Read from a block devic, write to a character device.  This
+    will read the entire block device and dump the contents in
+    the bit bucket.
+  </li>
+<ul><pre>
+nsh&gt; ls -l /dev
+/dev:
+ crw-rw-rw-       0 null
+ brw-rw-rw-       0 ram0
+nsh&gt; dd if=/dev/ram0 of=/dev/null
+</pre></ul>
+  </li>
+</ol>
 
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