  The Linux Ultra-DMA Mini-Howto
  Brion Vibber, brion@pobox.com
  v2.1, 27 May 1999

  This document is intended to explain how to use Ultra-DMA aka Ultra-
  ATA aka Ultra33 and Ultra66 hard drives and interfaces with Linux. The
  most recent version of this mini-Howto can be obtained in HTML format
  at http://pobox.com/~brion/linux/Ultra-DMA.html.
  ______________________________________________________________________

  Table of Contents


  1. Introduction

     1.1 Disclaimer
     1.2 Credits
     1.3 Document History
     1.4 Copying

  2. What is Ultra-DMA and why do I want it?

     2.1 IDE, EIDE, & ATAPI
     2.2 Bus Master DMA
     2.3 Ultra-DMA aka Ultra-ATA aka Ultra33 aka...
     2.4 Just how ``Ultra'' is it anyway?
     2.5 How does UDMA compare to SCSI?

  3. Using your UDMA hard drive with an EIDE interface

  4. Using your hard drives with a UDMA interface

  5. Offboard PCI UDMA interfaces

     5.1 Promise Ultra33
     5.2 Promise Ultra66
     5.3 Artop ATP850UF
     5.4 Adding device files

  6. Onboard UDMA interfaces

     6.1 Intel FX, HX, VX, TX, and LX
     6.2 The VIA VP2 and Related Chipsets
     6.3 TX Pro and other ``Pro'' boards

  7. UDMA-Generic

  8. Activating and Deactivating UDMA

     8.1 Using kernel boot parameters
     8.2 Using hdparm

  9. Problems

     9.1 The UDMA Blacklist
     9.2 Are you overclocking?
     9.3 Is your BIOS current?
     9.4 If you still can't get it to work!

  10. If you have some information about UDMA stuff that's not in this mini-howto...



  ______________________________________________________________________


  1.  Introduction


  This document is intended to explain how to use Ultra-DMA aka Ultra-
  ATA aka Ultra33 and Ultra66 hard drives and interfaces with Linux. In
  some cases there is no difficulty in using them, but some tweaking can
  increase performance. In other cases, you need to go to extraordinary
  lengths simply to access your hard drives.


  1.1.  Disclaimer


  The information in this is document is, to the best of my knowledge,
  correct, and should work. However, there may be typos, there may be
  mysterious transmission errors, and there may be strange
  incompatibilities within your own system that prevent the techniques
  described herein from working properly. So... before you go fiddling
  around with you hard drive, BACK UP ANY DATA YOU WANT TO KEEP! If you
  are not already performing regular backups, please start doing so for
  your own good.


  1.2.  Credits


  Michel Aubry <mailto:giovanni@sudfr.com> - UDMA-enabled VIA-related
  patch for <=2.0.33 & more info, grand unified UDMA patch for 2.0.34+

  Andrew Balsa <mailto:andrebalsa@altern.org> - Provided some general
  UDMA info and the udma-generic patch for Intel TX, SiS, and VP1 on
  <=2.0.33; also the grand unified UDMA patch for 2.0.34+

  Maxime Baudin - French translation

  Bokonon - ``Controller'' vs. ``interface''

  John G. <mailto:prefect@ipass.net> - VIA VP2 patch for <=2.0.33 & info

  Martin Gaitan - Promise Ultra33 ide0/ide1 installation workaround

  Andre M. Hedrick <mailto:hedrick@Astro.Dyer.Vanderbilt.Edu> - Grand
  unified UDMA patch for 2.0.34+, Artop ATP850UF

  Norman Jacobowitz - Bugged me to add info on the VP3

  John Levon - Info on TX Pro mobos

  Peter Monta - Info on using two Ultra33 cards

  Masayoshi Nakano - Japanese translation

  Gadi Oxman <mailto:gadio@netvision.net.il> - The Promise Ultra33 patch
  for <=2.0.34 & finding the secret numbers for the workaround

  Andy Pearce - Suggested adding info on the additional device files for
  hde-h

  Andrei Pitis <mailto:pink@roedu.net> - LILO patch

  Brion Vibber <mailto:brion@pobox.com> - The document itself





  1.3.  Document History


  v2.1, 27 May 1999: Corrects some minor omissions and errors from 2.0
  and adds information on the Promise Ultra66 and 2.2/2.3 kernels.

  v2.0, 7 August 1998: Major updates and almost total restructuring of
  the document into onboard (motherboard) and offboard (add-in cards)
  interfaces; the Grand Unified UDMA patch(a part of the Jumbo patch)
  for 2.0.35. Put credits in alphabetical order by last name. Changed
  ``controller'' to ``interface'' in many cases to be more technically
  correct. Added info on enabling/disabling UDMA, the blacklist, and
  more!

  v1.45, 6 July 1998: Minor updates - Red Hat 5.1 and 2.0.34 patch for
  Promise Ultra33, LILO patch for booting off of PCI interfaces such as
  the Promise Ultra33

  v1.41, 3 May 1998: Fixed a couple of typos, added translators to
  credits.

  v1.4, 28 April 1998: UDMA-Generic patch, some more general info.
  Copying section added.

  v1.3, 5 March 1998: VIA VP3 info, better patching instructions,
  pointer to more recent Promise patch.

  v1.2, 27 January 1998: Additional Promise workaround info.

  v1.1, 21 January 1998: New info about VIA chipset, installing around
  the Promise Ultra33, and enabling Bus Master & UDMA transfer modes.

  v1.0, 19 January 1998: More or less complete, first version done in
  SGML.


  1.4.  Copying


  This document may be freely copied and distributed for informational
  purposes. It may not be modified, except for reformatting, without the
  permission of the author. If you wish to translate this document into
  another language you may do so, however you should contact the author
  first so that updated versions of this document can be sent out to
  translators as well as directly to the Linux Documentation Project.


  2.  What is Ultra-DMA and why do I want it?


  Here's a brief overview of IDE-based drive technologies:


  2.1.  IDE, EIDE, & ATAPI


  These are older drive technologies. Most non-SCSI hard drives and
  drive interfaces that you can buy today or are likely to be using are
  EIDE, although many of the larger drives now available are UDMA.


  2.2.  Bus Master DMA


  Bus Master DMA is a technology for increasing the speed of hard disk
  data transfers which requires support from the motherboard and the
  BIOS, and at least some support from the drive.

  You can learn more at
  http://developer.intel.com/design/pcisets/busmastr/FAQs.htm.


  2.3.  Ultra-DMA aka Ultra-ATA aka Ultra33 aka...

  Ultra-DMA has many names, but we'll just call it UDMA in here.

  UDMA is a more advanced technology which provides for even faster
  throughput, up to 33.3 MB/s in UDMA mode 2 and 66.7 MB/s in UDMA mode
  4, twice to four times that of EIDE, for much lower prices than SCSI.
  Many new computers come with large UDMA drives and UDMA interfaces,
  and it's possible to add a UDMA interface card (such as the Promise
  Ultra33 or Ultra66) to an existing system to boost speed, even on
  older non-UDMA drives.

  You can learn great details about UDMA at
  http://www.quantum.com/src/whitepapers/ultraata/

  Note that cable length should be kept shorter for UDMA, compared to
  plain DMA, preferably less than 30 cm (12") maximum length. 66 MB/s
  requires a special cable and must be kept even shorter.


  2.4.  Just how ``Ultra'' is it anyway?


  Before we get any farther, let's clear up a misconception. That 33 or
  66 MB/sec figure is the burst transfer rate, and it's not something
  you're going to see very often. To explain, here is a clip from
  udma­generic's UDMA.txt:



       Burst (instantaneous) transfer rates are supposed to go from 16.6MB/s (PIO
       mode 4) to 16.6MB/s (DMA mode 2) up to 33MB/s (UDMA). In his patch against
       kernel 2.1.55, Kim-Hoe Pang actually checked the UDMA burst transfer rate
       with a logic analiser: 60ns/word, which translates into 33MB/s.

       Note that burst transfer rates only affect data transfers to/from the EIDE
       drive cache (476kB for the IBM 6.4GB drive), and IMHO are not particularly
       relevant for most Linux users.

       The Linux kernel uses as much RAM as possible to cache hard disk data
       accesses, and so if data is not in the kernel cache there is little chance
       that it will be in the (much smaller) hard disk cache.




  Much more relevant is the sustained transfer rate, the speed at which
  data can be transferred from the drive to main memory where it can be
  used. An easy way to measure the sustained transfer rate is to use
  hdparm, for instance ``hdparm ­Tt /dev/hda'' to measure the rate of
  the first IDE device.









  Here is some data gathered after extensive testing, using the hdparm utility
  (also written by Mark Lord):

  PIO mode 4 transfer rates under Linux:   +/- 5.2MB/s

  DMA mode 2 transfer rates under Linux:   +/- 7.2MB/s

  UDMA mode 2 transfer rates under Linux:  +/- 9.8MB/s




  As you can see, UDMA is still almost twice as fast as plain EIDE and
  significantly faster than plain bus mastering DMA.


  2.5.  How does UDMA compare to SCSI?


  I don't have any hard numbers to give you, but the general consensus
  is that high-end SCSI can give better performance than UDMA. However
  if you've looked at the price tags on any hard drives lately you'll
  notice that UDMA drives tend to be much less expensive. The
  performance/price ratio favors UDMA in most cases.


  3.  Using your UDMA hard drive with an EIDE interface


  This is easy to do. Since all UDMA drives are fully EIDE backward-
  compatible, just plunk your drive on your EIDE interface like it was
  any old hard drive and Linux should have no problems detecting or
  using it.  However, you will of course be limited to the slower speed
  of EIDE.


  4.  Using your hard drives with a UDMA interface


  Well, there is good news and there is bad news. The good news is that
  a UDMA interface can be used with both UDMA hard drives and legacy
  EIDE hard drives, and will be a lot faster than an EIDE interface.

  The bad news is that the old stock kernels (2.0.x) do not currently
  support UDMA very well. The new 2.2.x kernels do support UDMA33,
  however, and there are a number of kernel patches available for
  currently existing kernels. In addition, certain UDMA interfaces that
  are add-in cards rather than built into the motherboard require either
  a patch or some trickery to use on older kernels. That is why this
  document exists - to explain how to get the patches and work the
  trickery.


  5.  Offboard PCI UDMA interfaces


  These are UDMA interfaces on PCI cards that can be used to add UDMA
  support to an existing computer without replacing the motherboard, or
  for adding support for an additional four drives to a machine which
  has had its onboard interfaces filled. They can also be found
  preinstalled in some computers, especially Gateway 2000 and Dell
  machines.

  Most of them are not supported by the old stable kernels (2.0.x), but
  should work with a 2.2.x kernel - the Red Hat 6.0 and SuSE 6.1
  distributions are based on 2.2.x kernels, as are the most recent
  versions of most other distros.  However some of the latest cards (the
  Promise Ultra66 for instance) won't work even with the current 2.2.x
  kernels, if you have this or can't get a newer distribution then you
  must apply a kernel patch or upgrade to a newer kernel version.  If
  you need to install Linux onto a hard drive on one of these interfaces
  in this case, you will need to use a few odd tricks.


  5.1.  Promise Ultra33


  This is a PCI card that has two UDMA channels on it, supporting up to
  four drives total. You can look up specifications & pricing at
  http://www.promise.com.

  This card shipped in early model Gateway 2000 Pentium II systems, and
  may or may not be in more recent models.

  Kernels 2.0.35 and later and all 2.2.x kernels support the Ultra33 and
  you should have no trouble installing a distribution that uses these
  kernels.  However, the older stable kernels (2.0.34 and below) do not,
  and since most older Linux distributions include these older kernels
  it can be a little difficult to get Linux installed if you can't or
  don't want to use a newer version (for instance if you are
  standardized on a particular version of a distribution throughout your
  organization).

  Installing Linux with the Ultra33

  Although there is a patch for the Ultra33 interface, it is not very
  easy to apply a patch and recompile your kernel if you have not
  installed Linux yet! So, here is a workaround which allows you to
  install. Thanks to Gadi Oxman for the following information on getting
  the interface settings:



       If we can access the console with the installation disk, we can also
       use "cat /proc/pci" to display the Promise interface settings:

           RAID bus interface: Promise Technology Unknown device (rev 1).
             Vendor id=105a. Device id=4d33.
             Medium devsel.  IRQ 12.  Master Capable.  Latency=32.
             I/O at 0xe000.   (a)
             I/O at 0xd804.   (b)
             I/O at 0xd400.   (c)
             I/O at 0xd004.   (d)
             I/O at 0xc800.   (e)

       and pass "ide2=a,b+2 ide3=c,d+2" as a command line parameter to the kernel.




  Note that the numbers probably are not the same as what you will have.
  Just as an example, the parameters to use for the above set of numbers
  would be ``ide2=0xe000,0xd806 ide3=0xd400,0xd006''.  If you are only
  using the first channel on the Ultra33 (for instance, if you only have
  one drive, or two if they are master and slave on the same channel),
  then you won't need to specify ide3.

  Red Hat 5.1: Boot with the boot diskette and press enter when
  prompted.  The kernel will load, and then you will be asked for a
  language, keyboard type, and installation method. You may be prompted
  for additional information about the source media; it doesn't matter
  right now what you tell it as long as you can get to the next step.
  Next you should see a screen titled ``Select Installation Path'';
  press Alt-F2 now to get to a command prompt.  Run ``cat /proc/pci'',
  write down the numbers as above, and reboot from the boot disk. This
  time, type ``linux ide2= (this is where you put the numbers like shown
  above) ide3=(more numbers)''. It should now be able to install onto
  your hard disk without difficulty, however LILO will probably not be
  able to install; instead make a boot floppy and boot it with the same
  parameters until you can patch LILO and and the kernel.

  Red Hat 5.0 and Slackware 3.4: These are similar, but with the wrinkle
  that the setup programs ignore /dev/hde-h (the drives on ide2 and
  ide3).  In order to install to or from these drives it is necessary to
  override one or both of the onboard interface's channels. However be
  sure not to override a device that you need to install; for instance
  if you are installing from a CD-ROM drive on /dev/hdd (ide1 - onboard
  interface) to a hard drive on /dev/hde (ide2 - the Ultra33), you
  should override the non-essential ide0 with ide2 and leave ide1
  intact. Assuming the numbers above you would boot with
  ``ide0=0xe000,0xd806''. Red Hat 5.0 will give you a shell prompt if
  you use the rescue disk capability, and Slackware includes a shell in
  the regular installation process. However Red Hat 5.0 is difficult to
  boot after installation; if you have problems you could try
  downloading a Slackware boot disk from
  ftp://ftp.cdrom.com/pub/linux/slackware-3.5/bootdsks.144/ and using
  that to boot.

  With another Linux distribution you will have to improvise a bit, but
  the process should be about the same as the above.

  IMPORTANT: Without the patch (discussed in the section
  ``UDMA­Generic''), the kernel needs these boot parameters in order to
  access your hard disk! Therefore it is very important that when you
  configure LILO, either on the hard disk or on a boot floppy, that you
  give it the exact same parameters that you gave when installing.
  Otherwise your system won't boot! It should be possible to give them
  to LILO when you boot (ie, press Shift, type in ``linux ide2=.....''
  each time you boot), but only if you kept the numbers! It is
  recommended that you patch your kernel as soon as possible so you will
  not have to worry about that anymore; once you are booting with a
  patched kernel, you can get rid of the boot parameters. Also, as far
  as I know there is no way to pass boot parameters to a plain kernel
  boot floppy (as made with ``make zdisk''), you must use LILO or
  another loader (such as LOADLIN) that lets you pass boot parameters.

  However, unpatched kernels and installation programs often have a
  difficult time actually using ide2 and ide3, even if the drives are
  detected properly.  So if you can't get Linux to install using the
  above technique, try specifying ide0 or ide1 instead of ide2 or ide3
  (thanks to Martin Gaitan for this technique). This essentially
  replaces the on-board interface with the Promise Ultra33 as far as the
  kernel is concerned, and you can follow the directions in the next
  section as if you had physically moved it.  Note that if you're using
  an IDE CD-ROM drive connected to your on-board interface to install
  from, you will want to make sure that you do not take over the
  interface that the CD is on or you will not be able to install! If the
  CD is hda or hdb, use ide1 for your hard drive, and if it is hdc or
  hdd, then use ide0.

  Installing Linux Around the Ultra33

  If you cannot get the software workaround to work, you will have to
  try a more brute force approach. Here's an alternative method that is
  virtually guaranteed to work, but  will require you to open up your
  computer and mess about in it. NOTE: If you are not familiar with the
  process of connecting and disconnecting IDE drives, read the manuals
  that came with your computer, your hard drive, and/or the Promise
  Ultra33 before attempting this! If you screw something up and don't
  know how to put it back, you could end up being sorry!

  That being said, it's all really quite simple. Most motherboards these
  days have built-in EIDE interfaces. Disconnect your hard drive from
  the Ultra33 and connect it to the onboard interface. If you have other
  IDE devices, such as a CD-ROM, tape, or ZIP drive, on your oboard
  interface, it is easiest if you either add the hard drive on an unused
  channel (the secondary instead of the primary) or temporarily displace
  a device that you don not need immediately (such as ZIP or tape).
  Install Linux. Download and apply the Promise UDMA patch (see next
  section).

  Now you are ready to move the drive back onto the Promise... almost.
  To be safe, make a kernel-image boot floppy (cd /usr/src/linux ; make
  zdisk), which you  will be able to use to boot your system in case
  LILO doesn't work. Actually, to be very safe, make two and put one
  away for now.

  Okay, now it is time to think a little... if you have just one hard
  drive and it is going to be on the Promise, then it will most likely
  be /dev/hde (a and b are for the primary onboard interface, c and d
  for the secondary onboard interface).  If you are going to put any
  other drives on it, then the slave of the Promise's first channel will
  be /dev/hdf, the master of the second will be /dev/hdg, and the slave
  of the second will be /dev/hdh.

  Edit /etc/fstab, and change all the partitions of the hard drives you
  are moving from the onboard drives (/dev/hda, hdb, etc) to their new
  locations  on the Promise (/dev/hde, hdf, etc). If you had to displace
  any devices (such as a CD-ROM or ZIP drive) that you want to leave on
  the onboard interface, then change them to their new locations as
  well. For instance, if your CD-ROM was originally the master on the
  primary channel (/dev/hda), but you put your hard disk there and had
  to bump the CD to the slave  (/dev/hdb) or to the secondary channel
  (/dev/hdc), and now you want to put  it back, then change it to
  /dev/hda.

  If you are using LILO, reconfigure LILO to use the new location of the
  drive (LILO configuration is beyond the scope of this document, if you
  do not know how, read the LILO mini-HOWTO
  <http://sunsite.unc.edu/LDP/HOWTO/mini/LILO.html>), or else it
  probably will not be able to boot unless you use that boot floppy I
  had you make, which you will also want to configure to boot off the
  new partition. This is done using the rdev command. Put the floppy in
  the drive and type ``rdev /dev/fd0 /dev/hde1''. Of course that's
  assuming your root partition is the first on your first UDMA drive. If
  not (mine is /dev/hde7, for instance), then obviously use the
  appropriate partition number!

  Reboot. Your system should now work fine.

  Patching for the Ultra33

  Kernels 2.0.35 and later support the Promise Ultra33 natively;
  download an upgrade from your Linux distribution or from
  http://www.kernel.org.

  For instructions on how to compile the kernel, read the Kernel HOWTO.

  Using two Ultra33 cards in one machine

  This is currently not working correctly... don't do it right now
  unless you're willing to fiddle with the kernel to try to get things
  to work.

  5.2.  Promise Ultra66

  This is essentially the same as the Ultra33 with support for the new
  UDMA mode 4 66 MB/sec transfer speed. Unfortunately it is not yet
  supported by 2.2.x kernels.

  There is a patch for 2.0.x and 2.2.x kernels availabe at
  http://www.dyer.vanderbilt.edu/server/udma/, and support is included
  in the 2.3.x development kernel series at least as of 2.3.3.

  However to get far enough to patch or upgrade the kernel you'll have
  to pull the same dirty tricks as for the Ultra33 as in the section
  above.


  5.3.  Artop ATP850UF


  This card is supported by udma­generic. Installation of Linux onto a
  system with one of these as the interface for the target disk may be
  similar to the workarounds for the Promise Ultra33.


  5.4.  Adding device files


  The tertiary and quaternary IDE interfaces (ide2 and ide3) use device
  files of the form /dev/hde* through /dev/hdh*. On older kernels these
  devices were not automatically created, so you may need to add them
  manually for things to work properly.

  This can be done easily if you have a current copy of the Linux kernel
  source installed; simply run /usr/src/linux/scripts/MAKEDEV.ide and it
  will create all relevant device files.


  6.  Onboard UDMA interfaces


  These are UDMA­capable drive interfaces built into motherboards. They
  use the standard IDE I/O ports and so are fully usable at the slower
  non­UDMA speeds on an unpatched 2.0.x kernel such as are used when
  installing Linux.  Thus they should not cause any difficulties during
  installation, and patching for UDMA speed is a welcome luxury instead
  of a necessary step. Some UDMA support is in the latest 2.0.x kernels
  I believe, and is built into current 2.2.x kernels for the Intel
  chipsets.


  6.1.  Intel FX, HX, VX, TX, and LX


  Thanks again to Gadi for this info:



       Bus mastering DMA support for the Intel TX chipset is available in 2.0.31
       and above.




  In older kernels (such as Slackware 3.4's 2.0.30), the interface will
  be used in the slower EIDE mode.  In either case the interface will be
  automatically detected by the kernel and you should have no trouble
  using it.
  Full UDMA support for these chipsets is included in the udma­generic
  patch; see ``UDMA-Generic''.


  6.2.  The VIA VP2 and Related Chipsets


  This interface also can be autodetected and used in EIDE mode by an
  unpatched kernel, but if you have one of these, you will want to grab
  a patch so you can get faster throughput and do away with annoying
  "unkown PCI device" messages.

  One is available at http://www.ipass.net/~prefect/; it is designed for
  the VIA VP2/97 chipset, found on FIC's PA-2007 and PA-2011
  motherboards, but may work on related chipsets.  It has been reported
  that it functions on the newer VIA VP3 chipset, your mileage may vary.

  Note that this patch only supports Bus Mastering mode, not full UDMA
  mode, but it's still better than plain-vanilla EIDE mode.  Follow the
  directions at the patch's site for enabling BMDMA mode.

  There is another patch that supports full UDMA mode at
  http://www.pyreneesweb.com/Udma/udma.html, designed for the VIA
  VT82C586B, and it ought to work on the VP2, VP3, VPX, P6 and AGP
  Apollo chipsets. Follow the directions for installation and UDMA
  enabling there, but it is recommended that you back up any data you
  want to keep, as there are potential problems with incompatible
  motherboards. But, if it does work, it should work without problems.

  Note that the VP1 chipset is not known to work with these patches, but
  is supported by the ``UDMA-Generic'' patch.


  6.3.  TX Pro and other ``Pro'' boards


  UDMA is not currently supported for the TX Pro motherboards. They are
  not the same as a TX mobo, and apparently misreport their DMA
  capabilities hence the problem. Someone is working on this I hear, so
  a patch may appear some time in the future but not yet.


  7.  UDMA-Generic


  The UDMA-Generic patch, modified by André Balsa
  <mailto:andrebalsa@altern.org>, Andre Hedrick
  <mailto:hedrick@Astro.Dyer.Vanderbilt.Edu>, and Michel Aubry
  <mailto:giovanni@sudfr.com> from Mark Lord's original Triton DMA
  driver, provides UDMA support for the following chipsets (as of
  version 0.3):


  ˇ  All Intel chipsets: FX, HX, VX, TX, LX

  ˇ  All SiS chipsets (only SiS5598 tested, but this entire family of
     chipsets has the same bult-in 5513 interface device).

  ˇ  VIA chipsets (only 82C586B tested, but again this family of
     chipsets has the same interface structure). Special diagnostics
     support is available for the VIA interfaces.

  ˇ  Promise and Artop PCI UDMA interface cards support.  Triones PCI
     UDMA interface card not included yet.


  It is also designed to be easy to extend to support other chipsets.

  Udma-generic, also known as the Grand Unified UDMA Patch (GUUP -
  pronounced ``goop''), has been folded into the Jumbo patch which
  includes other useful features such as automatic detection of memory
  over 64 MB and CPU clock speed detection. Unfortunately this patch has
  vanished and I'm not entirely sure where to find that patch now, so
  instead one should go to  http://www.dyer.vanderbilt.edu/server/udma/
  where IDE/UDMA patches for current 2.0.x and and 2.2.x kernels can be
  found, now including support for the HPT343 and ALi15x3 chipsets.)

  Here are a few notes from the author:



       Performance with IBM UDMA drives on a good motherboard approches the
       maximum head transfer rates: about 10 Mb/s (measured with hdparm -t -T).

       The Intel TX chipset has a single FIFO for hard disk data shared by
       its two IDE interfaces, so using 2 UDMA drives will not yield such a
       great improvement over a single UDMA drive.
       However, the SiS5598 has two completely separate interfaces, each with
       its own FIFO. Theoretically, one could approach 66Mb/s burt transfer
       rates on motherboards with the SiS5598 chip, using the md driver and
       data striping over two drives. The SiS5571 has the same interface
       architecture, I think. I don't have the VIA chipsets datasheets, so I
       can't say anything about those.

       The Linux IDE (U)DMA kernel driver by Mark Lord has a particularly
       low setup time (i.e. latency for data transfers). It is ideal for
       frequent, small data transfers (such as those in Linux news servers),
       and might be in some cases superior to its SCSI counterparts.






  8.  Activating and Deactivating UDMA


  Normally, a UDMA-aware kernel will automatically enable UDMA support
  for drives and interfaces that support it. However starting with
  kernel 2.1.113 DMA drive transfers are disabled by default unless you
  have configured your kernel specifically to automatically activate it.
  This may seem inconvenient, but some drives and some interfaces do not
  function properly with DMA enabled; see the UDMA Blacklist below.


  8.1.  Using kernel boot parameters


  On kernels 2.1.113 and up, you can enable DMA for both drives on a
  given IDE interface using the ideX=dma kernel parameter, where X is
  the number of the interface (the first is 0).

  Kernel boot parameters can be set using LILO, LOADLIN, or most Linux
  boot loaders. For more information see the Bootdisk HOWTO.



  8.2.  Using hdparm


  hdparm is a program used to tweak the parameters of hard drives under
  Linux. Among other things you can use it to enable or disable UDMA for
  a drive and test its sustained transfer rate.

  The current version of hdparm, 3.5i as of this writing, is available
  at http://www.dyer.vanderbilt.edu/server/udma/.

  Compile and install it something like this:



       cd /usr/src
       tar zxvf /tmp/download/hdparm-3.5.tar.gz
       cd hdparm-3.3
       cat /tmp/download/hdparm-3.5i.patch | patch -p0
       make
       if [ -f /sbin/hdparm ]; then rm -f /sbin/hdparm ; fi
       make install
       cp /usr/local/sbin/hdparm /sbin/hdparm




  To enable DMA for a hard drive: hdparm -d1 /dev/hda

  To disable DMA for a hard drive: hdparm -d0 /dev/hda

  To measure transfer rate of a hard drive: hdparm -Tt /dev/hda

  To see what options are enabled for a hard drive: hdparm /dev/hda

  To see more info on your drive than you wanted to know: hdparm -i
  /dev/hda

  For more detailed info (such as how to choose which UDMA mode to use)
  read the man page (``man 8 hdparm'').


  9.  Problems

  9.1.  The UDMA Blacklist


  The following drives are ``blacklisted''. You should not use UDMA with
  these drives as it may cause corruption of data.


  ˇ  Western Digital WDC AC22100H

  The UDMA portion of the Jumbo-2.0.35-9 patch automatically disables
  DMA for this drive.


  9.2.  Are you overclocking?


  If you are, beware! Here is a quote from the udma-generic
  documentation:










  DON'T OVERCLOCK the PCI bus. 37.5MHz is the maximum supported speed for
  the PCI bus. Some (supposedly compatible) UDMA drives will not even take
  37.5MHz, but should be OK at 33.3MHz.

  In any case, NEVER, NEVER set the PCI bus to 41.5MHz.

  The RECOMMENDED safe setting is 33MHz.





  9.3.  Is your BIOS current?


  Here is another clip from the udma-generic docs:



       The real work involved in setting up the chips for DMA transfers is done
       mostly by the BIOS of each motherboard. Now of course one hopes that the
       BIOS has been correctly programmed...

       For example, the ASUS SP-97V motherboard with its original BIOS (Rev. 1.03)
       would malfunction with the modified Linux driver in both DMA mode 2 and UDMA
       modes; it would work well using PIO mode 4, or under Windows 95 in all
       modes. I downloaded the latest BIOS image (Rev. 1.06) from the ASUS Web site
       and flashed the BIOS EPROM with the latest BIOS revision. It has been
       working perfectly ever since (at 66 MHz bus speeds).

       What this tells us is that the BIOS sets up the DMA controller with specific
       timing parameters (active pulse and recovery clock cycles). My initial BIOS
       revision probably had bad timings. Since the Windows 95 driver sets up those
       timings by itself (i.e. it does not depend on the BIOS to setup the hard
       disk controller timing parameters), I initially had problems only with the
       Linux driver, while Windows 95 worked well.

       So, let me state this again: this Linux (U)DMA driver depends on the BIOS for
       correct (U)DMA controller setup. If you have problems, first check that you
       have the latest BIOS revision for your specific motherboard.

       ...

       New BIOS revisions can be downloaded from your motherboard manufacturer's
       Web site. Flashing a new BIOS image is a simple operation but one must
       strictly follow the steps explained on the motherboard manual.

       Late Award BIOS revisions seem stable with respect to UDMA. Anything with a
       date of 1998 should be fine.





  9.4.  If you still can't get it to work!


  If nothing in this document proved helpful, or at least not helpful
  enough to get your machine working, your best bet is to write up a
  message that fully describes your difficulty, what type of UDMA
  interface you have, whether it is onboard or on a card, if your drive
  is actually UDMA or plain EIDE, exactly what configuration of drives
  you have, what version (distribution & kernel versions if possible) of
  Linux you are using, and anything else that sounds useful, and post it
  to the newsgroup comp.os.linux.hardware.  You will probably get some
  helpful suggestions soon.
  10.  If you have some information about UDMA stuff that's not in this
  mini-howto...


  Great! If you know something I don't, by all means send it to me
  (brion@pobox.com) and I will put it in this document and update it
  fairly soon.



























































