-<chapter id="using-uio_dummy" xreflabel="Using uio_dummy">
-<?dbhtml filename="using-uio_dummy.html"?>
-<title>Using uio_dummy</title>
- <para>
- Well, there is no real use for uio_dummy. Its only purpose is
- to test most parts of the UIO system (everything except
- hardware interrupts), and to serve as an example for the
- kernel module that you will have to write yourself.
- </para>
-
-<sect1 id="what_uio_dummy_does">
-<title>What uio_dummy does</title>
- <para>
- The kernel module <filename>uio_dummy.ko</filename> creates a
- device that uses a timer to generate periodic interrupts. The
- interrupt handler does nothing but increment a counter. The
- driver adds two custom attributes, <varname>count</varname>
- and <varname>freq</varname>, that appear under
- <filename>/sys/devices/platform/uio_dummy/</filename>.
- </para>
-
- <para>
- The attribute <varname>count</varname> can be read and
- written. The associated file
- <filename>/sys/devices/platform/uio_dummy/count</filename>
- appears as a normal text file and contains the total number of
- timer interrupts. If you look at it (e.g. using
- <function>cat</function>), you'll notice it is slowly counting
- up.
- </para>
-
- <para>
- The attribute <varname>freq</varname> can be read and written.
- The content of
- <filename>/sys/devices/platform/uio_dummy/freq</filename>
- represents the number of system timer ticks between two timer
- interrupts. The default value of <varname>freq</varname> is
- the value of the kernel variable <varname>HZ</varname>, which
- gives you an interval of one second. Lower values will
- increase the frequency. Try the following:
- </para>
-<programlisting format="linespecific">
-cd /sys/devices/platform/uio_dummy/
-echo 100 > freq
-</programlisting>
- <para>
- Use <function>cat count</function> to see how the interrupt
- frequency changes.
- </para>
-</sect1>
-</chapter>
-