Command: irq

  USBDOS is a collection of different USB drivers and tools:
  IRQ shows you which Hardware Interrupt lines (IRQs or Interrupt
  ReQuest lines) on your computer are currently in use.


  IRQ number D


  The purpose of this program is to show you which Hardware Interrupt
  lines (IRQs or Interrupt ReQuest lines) on your computer are currently
  in use. You may want to know this simply as an academic exercise, or
  may need to know in order to configure or troubleshoot something.
  Note that in the output some of the IRQ descriptions are surrounded by
  *'s. This indicates that the particular interrupt is hard-wired on the
  motherboard, and is not available for use on external devices.
  In addition to just showing you which IRQs are enabled, this program
  can also enable or disable individual IRQs to help you identify and
  troubleshoot things. You should be EXTREMELY careful when you are doing
  this, however, since it can cause your computer to stop responding.
  To enable a particular IRQ, you simply give this program an IRQ number
  (a number between 0 and 15). To disable a particular IRQ, give this
  program an IRQ number (between 0 and 15) followed by another character
  (any character will do). For Example:
    IRQ  3       {Enable IRQ 3}
    IRQ 12 D     {Disable IRQ 12}


  There are a total of 16 IRQ's (Interrupt ReQuests) on your computer. An
  IRQ is also called a Hardware Interrupt, because it is "caused" by a
  hardware device of some sort. In some contexts, the word interrupt has
  a negative connotation, and is something you usually want to avoid. In
  a computer, though, an Interrupt is usually a good thing.
  Computers have 16 IRQ's, numbered 0-15. Some IRQ's are "hard-wired" to
  certain hardware Devices, such as the clocks inside the computer, the
  keyboard, and the math coprocessor. Others are there for "general use"
  (not hard-wired for a specific purpose), and can be used by most any
  hardware device, including USB Host Controllers. For an IRQ to be
  useful, it must be "wired" to a hardware device of some sort, and it
  must also be enabled.
  The view the status of the 16 IRQ's on your computer, you run IRQ with
  no option switches:
  This will show you which of the 16 IRQ's are enabled, which are hard-
  wired (and consequently not available for general-use), and what each
  of the general-use ones is commonly (but not always) used for. For
  instance, IRQ 3 is usually used for serial ports COM2 & COM4. However,
  IRQ 3 is not REQUIRED to be used for COM2 & COM4 -- it is actually a
  general-use IRQ and can be associated with any type of hardware device.
  Many newer computers only have one serial port (COM1) if they have any
  at all, and modern laptops usually don't have any built-in serial ports
  at all. An IRQ that is enabled was put that way by the BIOS as the
  computer was booting up, and does have some kind of hardware device
  "wired" to it. An IRQ that is disabled by the BIOS is probably not
  wired to any kind of hardware device (at least not one that is "turned
  on"), and is available to be used by a hardware device like a USB Host
  In addition to just showing you which IRQ's are currently enabled, the
  IRQ program also lets you turn the IRQ's on and off (enable and disable
  them). This is actually a useful troubleshooting tool in certain
  situations, such as the one I describe in the "IRQ & I/O
  Resources" section (page 56 of USBINTRO.DOC, see links below).
  To enable a particular IRQ, simply give the IRQ program an IRQ number
  (0-15) as an option switch. For example, to enable IRQ 4, you would do
  the following:
    IRQ 4
  To disable a particular IRQ, you must give the IRQ program an IRQ
  number followed by any character (any character at all). For example,
  to disable IRQ 4, you could do either of the following:
    IRQ 4 Disable
    IRQ 4 *
  While the IRQ program will let you enable and disable any of the 16
  available IRQ's (numbered 0-15), you should generally avoid disabling
  IRQ 0 (system timer), 1 (keyboard), and 2 (PIC controller #2).
  Disabling any of these will usually screw up your computer beyond
  repair (you'll need to reboot using the power switch to recover).
  Disabling (or enabling) any of the other IRQ's will USUALLY not screw
  anything up too badly, but exactly what happens will depend on what
  hardware (if any) is wired to the IRQ.

  As described in the "IRQ & I/O Resources" section (page 56 of
  USBINTRO.DOC, see links below), I was having a problem with the USB
  Host Controller on my laptop. Basically, the software (as configured
  by the BIOS) was lying to me about which IRQ the USB Host Controller
  was using. The software said it was using IRQ 5 when it was actually
  using IRQ 7. The way I found the real IRQ was to attach a Legacy
  Support Device (in my case, a USB Mouse) to the Root Hub, which would
  work as soon as the computer turned on. I then disabled the IRQ's
  one at a time (using the IRQ program), until I found out when the USB
  Mouse (the USB Host Controller) stopped working. After I figured out
  what the problem was, I "fixed" it in my AUTOEXEC.BAT file
  so I don't need to remember how to fix it each time.

  For more information see:
    C:\FREEDOS\DOC\usbintro.doc (too big for edit, please use
    another editor, e.g. Blocek!)


  IRQ      Shows the IRQs currently in use
  IRQ 3    (Enable IRQ 3 - Shown as "Enabled:  YES)
  IRQ 3 U  (Disable IRQ 3 - Shown as "Enabled: nothing)

See also:


  Copyright © 2008, Bret E. Johnson, help version 2023 W. Spiegl

  This file is derived from the FreeDOS Spec Command HOWTO.
  See the file H2Cpying for copying conditions.