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<a name="Memory-Map-Format"></a>
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<a name="Memory-Map-Format-1"></a>
<h3 class="section">E.16 Memory Map Format</h3>
<a name="index-memory-map-format"></a>

<p>To be able to write into flash memory, <small>GDB</small> needs to obtain a
memory map from the target.  This section describes the format of the
memory map.
</p>
<p>The memory map is obtained using the &lsquo;<samp>qXfer:memory-map:read</samp>&rsquo;
(see <a href="General-Query-Packets.html#qXfer-memory-map-read">qXfer memory map read</a>) packet and is an XML document that
lists memory regions.
</p>
<p><small>GDB</small> must be linked with the Expat library to support XML
memory maps.  See <a href="Requirements.html#Expat">Expat</a>.
</p>
<p>The top-level structure of the document is shown below:
</p>
<div class="smallexample">
<pre class="smallexample">&lt;?xml version=&quot;1.0&quot;?&gt;
&lt;!DOCTYPE memory-map
          PUBLIC &quot;+//IDN gnu.org//DTD GDB Memory Map V1.0//EN&quot;
                 &quot;http://sourceware.org/gdb/gdb-memory-map.dtd&quot;&gt;
&lt;memory-map&gt;
    region...
&lt;/memory-map&gt;
</pre></div>

<p>Each region can be either:
</p>
<ul>
<li> A region of RAM starting at <var>addr</var> and extending for <var>length</var>
bytes from there:

<div class="smallexample">
<pre class="smallexample">&lt;memory type=&quot;ram&quot; start=&quot;<var>addr</var>&quot; length=&quot;<var>length</var>&quot;/&gt;
</pre></div>


</li><li> A region of read-only memory:

<div class="smallexample">
<pre class="smallexample">&lt;memory type=&quot;rom&quot; start=&quot;<var>addr</var>&quot; length=&quot;<var>length</var>&quot;/&gt;
</pre></div>


</li><li> A region of flash memory, with erasure blocks <var>blocksize</var>
bytes in length:

<div class="smallexample">
<pre class="smallexample">&lt;memory type=&quot;flash&quot; start=&quot;<var>addr</var>&quot; length=&quot;<var>length</var>&quot;&gt;
  &lt;property name=&quot;blocksize&quot;&gt;<var>blocksize</var>&lt;/property&gt;
&lt;/memory&gt;
</pre></div>

</li></ul>

<p>Regions must not overlap.  <small>GDB</small> assumes that areas of memory not covered
by the memory map are RAM, and uses the ordinary &lsquo;<samp>M</samp>&rsquo; and &lsquo;<samp>X</samp>&rsquo;
packets to write to addresses in such ranges.
</p>
<p>The formal DTD for memory map format is given below:
</p>
<div class="smallexample">
<pre class="smallexample">&lt;!-- ................................................... --&gt;
&lt;!-- Memory Map XML DTD ................................ --&gt;
&lt;!-- File: memory-map.dtd .............................. --&gt;
&lt;!-- .................................... .............. --&gt;
&lt;!-- memory-map.dtd --&gt;
&lt;!-- memory-map: Root element with versioning --&gt;
&lt;!ELEMENT memory-map (memory)*&gt;
&lt;!ATTLIST memory-map    version CDATA   #FIXED  &quot;1.0.0&quot;&gt;
&lt;!ELEMENT memory (property)*&gt;
&lt;!-- memory: Specifies a memory region,
             and its type, or device. --&gt;
&lt;!ATTLIST memory        type    (ram|rom|flash) #REQUIRED
                        start   CDATA   #REQUIRED
                        length  CDATA   #REQUIRED&gt;
&lt;!-- property: Generic attribute tag --&gt;
&lt;!ELEMENT property (#PCDATA | property)*&gt;
&lt;!ATTLIST property      name    (blocksize) #REQUIRED&gt;
</pre></div>

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