111 lines
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111 lines
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<!Converted with LaTeX2HTML 95.1 (Fri Jan 20 1995) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<TITLE>2.5.2.1 Isolating hardware problems</TITLE>
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<B> Next:</B> <A NAME=tex2html2770 HREF="node85.html">2.5.2.2 Problems recognizing hard </A>
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<B>Up:</B> <A NAME=tex2html2768 HREF="node83.html">2.5.2 Hardware problems</A>
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<B> Previous:</B> <A NAME=tex2html2762 HREF="node83.html">2.5.2 Hardware problems</A>
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<H3><A NAME=SECTION00452100000000000000>2.5.2.1 Isolating hardware problems</A></H3>
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<P>
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<A NAME=secinstallprobshardwareconflicts> </A>
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<P>
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<A NAME=1584> </A>
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<P>
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If you experience a problem that you believe to be hardware-related,
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the first thing that you should to do is attempt to isolate the problem.
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This means eliminating all possible variables and (usually) taking the
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system apart, piece-by-piece, until the offending piece of hardware is
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isolated.
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<P>
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This is not as frightening as it may sound. Basically, you should remove
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all nonessential hardware from your system, and then determine which
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device is actually causing the trouble---possibly by reinserting each
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device, one at a time. This means that you should remove all hardware other
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than the floppy and video controllers, and of course the keyboard. Even
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innocent-looking devices such as mouse controllers can wreak unknown havoc on
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your peace of mind unless you consider them nonessential.
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<P>
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For example, let's say that the system hangs during the Ethernet board detection
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sequence at boot time. You might hypothesize that there is a conflict or
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problem with the Ethernet board in your machine. The quick and easy way to
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find out is to pull the Ethernet board, and try booting again. If everything
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goes well, then you know that either (a) the Ethernet board is not
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supported by Linux (see Section <A HREF="node30.html#secintrohardware">1.8</A> for a list
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of compatible boards), or (b) there is an address or IRQ conflict with the
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board.
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<P>
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<A NAME=1586> </A>
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``Address or IRQ conflict?'' What on earth does that mean?
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All devices in your machine use an <em>IRQ</em>, or
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<em>interrupt request line</em>, to tell the system that they need something
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done on their behalf. You can think of the IRQ as a cord that the device
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tugs when it needs the system to take care of some pending request.
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If more than one
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device is tugging on the same cord, the kernel won't be able to detemine
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which device it needs to service. Instant mayhem.
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<P>
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Therefore, be sure that all of your installed devices are using unique
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IRQ lines. In general the IRQ for a device can be set by jumpers on the
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card; see the documentation for the particular device for details.
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Some devices do not require the use of an IRQ at all, but it is suggested
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that you configure them to use one if possible (the Seagate ST01 and ST02
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SCSI controllers being good examples).
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<P>
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In some cases, the kernel provided on your installation media is configured
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to use a certain IRQ for certain devices. For example, on some distributions
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of Linux, the kernel is preconfigured to use IRQ 5 for the TMC-950 SCSI
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controller, the Mitsumi CD-ROM controller, and the bus mouse driver.
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If you want to use two or more of these devices, you'll need to first
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install Linux with only one of these devices enabled, then recompile the
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kernel in order to change the default IRQ for one of them.
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(See Chapter <A HREF="node155.html#chapsysadmnum">4</A> for information
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on recompiling the kernel.)
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<P>
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Another area where hardware conflicts can arise is with DMA (direct
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memory access) channels, I/O addresses, and shared memory addresses.
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All of these terms describe mechanisms through which the system interfaces
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with hardware devices. Some Ethernet boards, for example, use a shared memory
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address as well as an IRQ to interface with the system. If any of these
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are in conflict with other devices, then the system may behave unexpectedly.
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You should be able to change the DMA channel, I/O or shared
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memory addresses for your various devices with jumper settings. (Unfortunately,
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some devices don't allow you to change these settings.)
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<P>
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The documentation for your various hardware devices should specify
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the IRQ, DMA channel, I/O address, or shared memory address that the devices
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use, and how to configure them. Again, the simple way to get around these
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problems is just to temporarily disable the conflicting devices until you
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have time to determine the cause of the problem.
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<P>
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Table <A HREF="node84.html#tabledevsettings">2.2</A> is a list of IRQ and DMA channels used by
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various ``standard'' devices found on most systems. Almost all systems will
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have some of these devices, so you should avoid setting the IRQ or DMA of other
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devices in conflict with these values.
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<P>
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<P><A NAME=1612> </A><A NAME=tabledevsettings> </A><IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img71.gif">
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<BR><STRONG>Table 2.2:</STRONG> Common device settings<BR>
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<P>
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<P>
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<A NAME=1616> </A>
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<P>
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<BR> <HR><A NAME=tex2html2769 HREF="node85.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A> <A NAME=tex2html2767 HREF="node83.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A> <A NAME=tex2html2761 HREF="node83.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="previous_motif.gif"></A> <A NAME=tex2html2771 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <A NAME=tex2html2772 HREF="node250.html"><IMG ALIGN=BOTTOM ALT="index" SRC="index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2770 HREF="node85.html">2.5.2.2 Problems recognizing hard </A>
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<B>Up:</B> <A NAME=tex2html2768 HREF="node83.html">2.5.2 Hardware problems</A>
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<B> Previous:</B> <A NAME=tex2html2762 HREF="node83.html">2.5.2 Hardware problems</A>
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<BR> <HR> <P>
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<BR> <HR>
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<P><ADDRESS>
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<I>Matt Welsh <BR>
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mdw@sunsite.unc.edu</I>
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