fix regressions, remove obsolete description of isapnp support
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Frank Mori Hess
parent
f98e8f792e
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5cc75f5efe
3 changed files with 51 additions and 47 deletions
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@ -27,76 +27,50 @@ the <command>comedi_config</command> command. (As root of course.)
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Here is an example of how to use the command (perhaps you should read
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its <command>man</command> page now):
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<screen>
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/usr/sbin/comedi_config /dev/comedi0 ni_atmio 0x260,3
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PATH=/sbin:/usr/sbin:/usr/local/sbin:$PATH
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comedi_config /dev/comedi0 labpc-1200 0x260,3
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</screen>
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This command says that the “file”
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<filename>/dev/comedi0</filename> can be used to access the &comedi;
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device that uses the <parameter>ni_atmio</parameter> driver, and that
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device that uses the <parameter>labpc-1200</parameter> board, and that
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you give it two run-time parameters (<literal>0x260</literal> and
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<literal>3</literal>). More parameters are possible, for example to
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discriminate between two or more identical cards in your system.
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</para>
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<para>
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If you want to have the board configured in this way every time you
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boot, put the line above into a start-up script file of your Linux
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boot, put the lines above into a start-up script file of your Linux
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system (for example, the
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<filename>/etc/rc.d/rc.local</filename> file), or in the system-wide
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&comedi; configuration file <filename>/etc/comedi.conf</filename>.
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You can, of course, also run this command at a command prompt.
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<filename>/etc/rc.d/rc.local</filename> file), or for PCMCIA
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boards the appropriate place is the /etc/pcmcia/comedi script.
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For non-PCMCIA boards, you can also arrange to have your driver
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loaded and comedi_config run with by adding a few lines
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to /etc/modules.conf (see the INSTALL file for the comedi
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kernel modules). You can, of course, also run comedi_config
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at a command prompt.
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</para>
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<para>
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This tutorial goes through the process of configuring &comedi;
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for two devices, a
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<literal>National Instruments AT-MIO-16E-10</literal> (which has the
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driver mentioned above), and a
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<literal>National Instruments AT-MIO-16E-10</literal>, and a
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<literal>Data Translation DT2821-F-8DI</literal>.
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</para>
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<para>
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The NI board is plug-and-play, and the <command>man</command> page
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tells you that you need to configure the PnP part of the board with
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<command>isapnptools</command>. The <command>isapnptools</command>
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package is a little cryptic, but the concepts are simple. Once you've
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learned how to use it, you can settle on a
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<filename>/etc/isapnp.conf</filename> file such as this:
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</para>
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The NI board is plug-and-play. The current ni_atmio driver
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has kernel-level ISAPNP support, which is used by default
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if you do not specify a base address. So you could simply
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run comedi_config as
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<screen>
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# ANSI string -->National Instruments, AT-MIO-16E-10<--
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(CONFIGURE NIC2400/10725401 (LD 0
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(IO 0 (BASE 0x0260))
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(INT 0 (IRQ 3 (MODE +E)))
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# (DMA 0 (CHANNEL 5))
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# (DMA 1 (CHANNEL 6))
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(ACT Y)
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))
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comedi_config /dev/comedi0 ni_atmio
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</screen>
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<para>
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(This file also contains a few lines about overall configuration and
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about the sound card that happens to be in the same computer.)
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Currently, the driver doesn't use DMA, but it may in the future, so
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the DMA lines are commented out. It has been reported that the
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National Instruments board does not always work with interrupts other
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than IRQ 3, and that the device ignores the IRQ and DMA information
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given here. However, keep the information here to remind yourself that
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the numbers aren't arbitrary.
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</para>
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<para>
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The <command>man</command> page
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explains that the option list is supposed to be
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“<literal>(I/O base),(IRQ)</literal>”, so use the same
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numbers as in <filename>/etc/isapnp.conf</filename>, i.e.,
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<literal>0x260,3</literal>.
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</para>
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<para>
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For the <literal>Data Translation</literal> board, you need to have a
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list of the jumper settings; these are given in the &comedi; manual
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section about this card. (Check first to see whether they are still
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correct!)
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correct!)
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The card discussed her is a <literal>DT2821-f-8di</literal>. The
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<command>man</command> page of <command>comedi_config</command> tells
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you that you need to know the I/O base, IRQ, DMA 1, DMA 2. However,
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@ -131,7 +105,7 @@ So, the appropriate options list is:
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</screen>
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and the full configuration command is:
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<screen>
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/usr/sbin/comedi_config /dev/comedi1 dt2821-f-8di 0x200,4,,1,1,1
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comedi_config /dev/comedi1 dt2821-f-8di 0x200,4,,1,1,1
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</screen>
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The differential/single-ended number is left blank, since the
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driver already knowns (from the board name), that it is
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@ -998,7 +998,37 @@ data structure, and has no function at present.
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</section>
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<section>
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<title>
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Anti-aliasing
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</title>
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<para>
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If you wish to aquire accurate waveforms, it is vital that you use an
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anti-alias filter. An anti-alias filter is a low-pass filter used to
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remove all frequencies higher than the Nyquist frequency (half your sampling rate)
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from your analog input signal
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before you convert it to digital. If you fail to filter your input signal,
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any high frequency components in the original analog signal will create
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artifacts in your recorded digital waveform that cannot be corrected.
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</para>
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<para>
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For example, suppose you are sampling an analog input channel at a rate of
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1000 Hz. If you were to apply a 900 Hz sine wave to the input, you
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would find that your
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sampling rate is not high enough to faithfully record the 900 Hz input,
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since it is above your Nyquist frequency of 500 Hz. Instead, what you
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will see in your recorded digital waveform is a 100 Hz sine wave! If you
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don't use an anti-alias filter, it is impossible to tell whether the 100
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Hz sine wave you see in your digital signal was really produced by a
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100 Hz input signal, or a 900 Hz signal aliased to 100 Hz, or a 1100 Hz
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signal, etc.
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</para>
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<para>
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In practice, the cutoff frequency for the anti-alias filter is usually
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set 10% to 20% below the Nyquist frequency due to fact that real filters
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do not have infinitely sharp cutoffs.
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</para>
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</section>
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</section>
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@ -1,4 +1,4 @@
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<!-- <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook V3.1//EN" "docbook/dtd/3.1/docbook.dtd"> -->
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<!-- <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook V3.1//EN" -->
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<section id="comedi-comedilib-h">
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<title>
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