1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>mmap() device memory</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="The Userspace I/O HOWTO"><link rel="up" href="userspace_driver.html" title="Chapter&#160;4.&#160;Writing a driver in userspace"><link rel="prev" href="userspace_driver.html" title="Chapter&#160;4.&#160;Writing a driver in userspace"><link rel="next" href="wait_for_interrupts.html" title="Waiting for interrupts"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">mmap() device memory</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="userspace_driver.html">Prev</a>&#160;</td><th width="60%" align="center">Chapter&#160;4.&#160;Writing a driver in userspace</th><td width="20%" align="right">&#160;<a accesskey="n" href="wait_for_interrupts.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="mmap_device_memory"></a>mmap() device memory</h2></div></div></div><p>
2	After you made sure you've got the right device with the
3	memory mappings you need, all you have to do is to call
4	<code class="function">mmap()</code> to map the device's memory
5	to userspace.
6	</p><p>
7	The parameter <code class="varname">offset</code> of the
8	<code class="function">mmap()</code> call has a special meaning
9	for UIO devices: It is used to select which mapping of
10	your device you want to map. To map the memory of
11	mapping N, you have to use N times the page size as
12	your offset:
13	</p><pre class="programlisting">
14	offset = N * getpagesize();
15</pre><p>
16	N starts from zero, so if you've got only one memory
17	range to map, set <code class="varname">offset = 0</code>.
18	A drawback of this technique is that memory is always
19	mapped beginning with its start address.
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