path: root/Documentation/floppy.txt
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authorLinus Torvalds <>2005-04-16 15:20:36 -0700
committerLinus Torvalds <>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/floppy.txt
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+This file describes the floppy driver.
+FAQ list:
+ A FAQ list may be found in the fdutils package (see below), and also
+LILO configuration options (Thinkpad users, read this)
+ The floppy driver is configured using the 'floppy=' option in
+lilo. This option can be typed at the boot prompt, or entered in the
+lilo configuration file.
+ Example: If your kernel is called linux-2.6.9, type the following line
+at the lilo boot prompt (if you have a thinkpad):
+ linux-2.6.9 floppy=thinkpad
+You may also enter the following line in /etc/lilo.conf, in the description
+of linux-2.6.9:
+ append = "floppy=thinkpad"
+ Several floppy related options may be given, example:
+ linux-2.6.9 floppy=daring floppy=two_fdc
+ append = "floppy=daring floppy=two_fdc"
+ If you give options both in the lilo config file and on the boot
+prompt, the option strings of both places are concatenated, the boot
+prompt options coming last. That's why there are also options to
+restore the default behavior.
+Module configuration options
+ If you use the floppy driver as a module, use the following syntax:
+modprobe floppy <options>
+ modprobe floppy omnibook messages
+ If you need certain options enabled every time you load the floppy driver,
+you can put:
+ options floppy omnibook messages
+in /etc/modprobe.conf.
+ The floppy driver related options are:
+ floppy=asus_pci
+ Sets the bit mask to allow only units 0 and 1. (default)
+ floppy=daring
+ Tells the floppy driver that you have a well behaved floppy controller.
+ This allows more efficient and smoother operation, but may fail on
+ certain controllers. This may speed up certain operations.
+ floppy=0,daring
+ Tells the floppy driver that your floppy controller should be used
+ with caution.
+ floppy=one_fdc
+ Tells the floppy driver that you have only one floppy controller.
+ (default)
+ floppy=two_fdc
+ floppy=<address>,two_fdc
+ Tells the floppy driver that you have two floppy controllers.
+ The second floppy controller is assumed to be at <address>.
+ This option is not needed if the second controller is at address
+ 0x370, and if you use the 'cmos' option.
+ floppy=thinkpad
+ Tells the floppy driver that you have a Thinkpad. Thinkpads use an
+ inverted convention for the disk change line.
+ floppy=0,thinkpad
+ Tells the floppy driver that you don't have a Thinkpad.
+ floppy=omnibook
+ floppy=nodma
+ Tells the floppy driver not to use Dma for data transfers.
+ This is needed on HP Omnibooks, which don't have a workable
+ DMA channel for the floppy driver. This option is also useful
+ if you frequently get "Unable to allocate DMA memory" messages.
+ Indeed, dma memory needs to be continuous in physical memory,
+ and is thus harder to find, whereas non-dma buffers may be
+ allocated in virtual memory. However, I advise against this if
+ you have an FDC without a FIFO (8272A or 82072). 82072A and
+ later are OK. You also need at least a 486 to use nodma.
+ If you use nodma mode, I suggest you also set the FIFO
+ threshold to 10 or lower, in order to limit the number of data
+ transfer interrupts.
+ If you have a FIFO-able FDC, the floppy driver automatically
+ falls back on non DMA mode if no DMA-able memory can be found.
+ If you want to avoid this, explicitly ask for 'yesdma'.
+ floppy=yesdma
+ Tells the floppy driver that a workable DMA channel is available.
+ (default)
+ floppy=nofifo
+ Disables the FIFO entirely. This is needed if you get "Bus
+ master arbitration error" messages from your Ethernet card (or
+ from other devices) while accessing the floppy.
+ floppy=usefifo
+ Enables the FIFO. (default)
+ floppy=<threshold>,fifo_depth
+ Sets the FIFO threshold. This is mostly relevant in DMA
+ mode. If this is higher, the floppy driver tolerates more
+ interrupt latency, but it triggers more interrupts (i.e. it
+ imposes more load on the rest of the system). If this is
+ lower, the interrupt latency should be lower too (faster
+ processor). The benefit of a lower threshold is less
+ interrupts.
+ To tune the fifo threshold, switch on over/underrun messages
+ using 'floppycontrol --messages'. Then access a floppy
+ disk. If you get a huge amount of "Over/Underrun - retrying"
+ messages, then the fifo threshold is too low. Try with a
+ higher value, until you only get an occasional Over/Underrun.
+ It is a good idea to compile the floppy driver as a module
+ when doing this tuning. Indeed, it allows to try different
+ fifo values without rebooting the machine for each test. Note
+ that you need to do 'floppycontrol --messages' every time you
+ re-insert the module.
+ Usually, tuning the fifo threshold should not be needed, as
+ the default (0xa) is reasonable.
+ floppy=<drive>,<type>,cmos
+ Sets the CMOS type of <drive> to <type>. This is mandatory if
+ you have more than two floppy drives (only two can be
+ described in the physical CMOS), or if your BIOS uses
+ non-standard CMOS types. The CMOS types are:
+ 0 - Use the value of the physical CMOS
+ 1 - 5 1/4 DD
+ 2 - 5 1/4 HD
+ 3 - 3 1/2 DD
+ 4 - 3 1/2 HD
+ 5 - 3 1/2 ED
+ 6 - 3 1/2 ED
+ 16 - unknown or not installed
+ (Note: there are two valid types for ED drives. This is because 5 was
+ initially chosen to represent floppy *tapes*, and 6 for ED drives.
+ AMI ignored this, and used 5 for ED drives. That's why the floppy
+ driver handles both.)
+ floppy=unexpected_interrupts
+ Print a warning message when an unexpected interrupt is received.
+ (default)
+ floppy=no_unexpected_interrupts
+ floppy=L40SX
+ Don't print a message when an unexpected interrupt is received. This
+ is needed on IBM L40SX laptops in certain video modes. (There seems
+ to be an interaction between video and floppy. The unexpected
+ interrupts affect only performance, and can be safely ignored.)
+ floppy=broken_dcl
+ Don't use the disk change line, but assume that the disk was
+ changed whenever the device node is reopened. Needed on some
+ boxes where the disk change line is broken or unsupported.
+ This should be regarded as a stopgap measure, indeed it makes
+ floppy operation less efficient due to unneeded cache
+ flushings, and slightly more unreliable. Please verify your
+ cable, connection and jumper settings if you have any DCL
+ problems. However, some older drives, and also some laptops
+ are known not to have a DCL.
+ floppy=debug
+ Print debugging messages.
+ floppy=messages
+ Print informational messages for some operations (disk change
+ notifications, warnings about over and underruns, and about
+ autodetection).
+ floppy=silent_dcl_clear
+ Uses a less noisy way to clear the disk change line (which
+ doesn't involve seeks). Implied by 'daring' option.
+ floppy=<nr>,irq
+ Sets the floppy IRQ to <nr> instead of 6.
+ floppy=<nr>,dma
+ Sets the floppy DMA channel to <nr> instead of 2.
+ floppy=slow
+ Use PS/2 stepping rate:
+ " PS/2 floppies have much slower step rates than regular floppies.
+ It's been recommended that take about 1/4 of the default speed
+ in some more extreme cases."
+Supporting utilities and additional documentation:
+ Additional parameters of the floppy driver can be configured at
+runtime. Utilities which do this can be found in the fdutils package.
+This package also contains a new version of mtools which allows to
+access high capacity disks (up to 1992K on a high density 3 1/2 disk!).
+It also contains additional documentation about the floppy driver.
+The latest version can be found at fdutils homepage:
+The fdutils-5.4 release can be found at:
+Reporting problems about the floppy driver
+ If you have a question or a bug report about the floppy driver, mail
+me at . If you post to Usenet, preferably use
+comp.os.linux.hardware. As the volume in these groups is rather high,
+be sure to include the word "floppy" (or "FLOPPY") in the subject
+line. If the reported problem happens when mounting floppy disks, be
+sure to mention also the type of the filesystem in the subject line.
+ Be sure to read the FAQ before mailing/posting any bug reports!
+ Alain
+10-30-2004 : Cleanup, updating, add reference to module configuration.
+ James Nelson <>
+6-3-2000 : Original Document