Q99859: Windows for Workgroups: Avoiding Hardware Conflicts
Article: Q99859
Product(s): Microsoft Windows 3.x Retail Product
Version(s): WINDOWS:3.1,3.11
Operating System(s):
Keyword(s):
Last Modified: 18-SEP-1999
3.10 3.11
WINDOWS
kbnetwork kbdisplay kbsound kbfasttip kbsetup kbtshoot
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The information in this article applies to:
- Microsoft Windows for Workgroups
- Microsoft Windows versions 3.1, 3.11
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SUMMARY
=======
This article summarizes four possible sources of hardware conflicts: IRQ lines,
upper memory address (UMA), base I/O address, and DMA channels. It also briefly
describes the function of each and suggests a strategy for diagnosing and/or
preventing hardware conflicts.
MORE INFORMATION
================
When you install peripheral devices, there are four possible sources of hardware
conflicts. (Not all devices use all four parameters or settings, although some
do. Most use IRQ, base I/O address, and/or UMA.) The key to avoiding hardware
conflicts is to ensure that no two devices are configured to use any of the same
settings.
A wide variety of symptoms may indicate hardware conflicts. These include system
hangs, general protection (GP) faults (and other error messages), corrupted
video displays, corrupted printing, limited functionality from one or more
installed devices, intermittent performance, and so on.
Diagnostic programs, such as Microsoft Diagnostics (MSD), can sometimes help
determine which IRQs and upper memory ranges are in use and which are available.
Currently, however, computer card manufacturers do not adhere to any industry
standard for reporting the current status of a card when probed by diagnostic
software. Therefore, the only accurate way to determine the current settings for
a card is to consult the manufacturer's documentation or inspect each card.
IRQs and DMA channels are single numbers (for example 1, 3, or 7). I/O base and
upper memory addresses include or cover a range (for example, D000-D800 or
360h-380h). Typically, these settings are chosen through DIP switches or jumpers
on the card. Sometimes the cards are software configurable or both hardware and
software configurable. For more information, consult your manufacturer's
documentation.
IRQ
---
An interrupt request line (IRQ) is a line trace etched on the circuit board from
the expansion slot to the programmable interrupt controller (PIC) chip through
which a peripheral device can notify the CPU. Under most circumstances, each
device must use its own IRQ line. IBM PC/AT-compatible design architecture
provides for a possibility of 16 IRQ lines (0-15), some of which are reserved
for standard devices such as the keyboard, floppy disk drives, the system clock,
and so forth. Communication (COM) ports 1 and 3 typically share IRQ 4; COM ports
2 and 4 share IRQ 3. Therefore, a potential conflict exists if devices are
installed on both COM ports 1 and 3 or on COM ports 2 and 4.
Available IRQ lines (for sound cards, network adapters, scanners, bus mouse,
video adapters, tape drives, SCSI interfaces, and so forth) usually include IRQs
5, 9, 10, 11, 12, 13, and 15. 8-bit expansion slots provide access to IRQs
through 7. 16-bit slots generally provide access to IRQs through 15.
Not all devices allow the selection of any IRQ number. Consult the device's
manufacturer or its documentation for information on which IRQs can be used by a
particular device and select an IRQ that does not conflict with currently
installed devices; or, change an installed device's IRQ to a different one to
make available an IRQ for the new device.
NOTE: You may need to reconfigure application software settings after changing
IRQs of previously installed devices.
UMA
---
A device's upper memory address (UMA) is a range of address space somewhere
between A000 and FFFF for use by the device. This corresponds to "using" some
portion of memory between 640 kilobytes (K) and 1 megabyte (MB). While physical
system RAM cannot be used by the device, the "addresses" are used and are
therefore unavailable to the system or other devices.
Conflicts can occur if two hardware devices try to occupy the same address range
or if an application, a device driver, or a terminate-and-stay-resident (TSR)
program does not detect that this address range is already in use and tries to
occupy it.
The entire UMA range is the same range shared by the video adapter (A000-CFFF
typically), the system ROM (0FFF-FFFF typically), and any installed cards that
use UMAs. Furthermore, loading device drivers and TSR programs high places them
in this range as well and can increase the potential for conflicts to occur.
To avoid UMA conflicts, use the following suggestions:
- Install cards before you optimize your upper memory area. If you have already
optimized the UMA and need to add a new card, load everything low, add the
new card, and then try to load items high. Optimizing the UMA after
installing cards avoids fragmenting the UMA range. This may allow more (or
larger) TSR programs and/or device drivers to be loaded high.
- Carefully plan the use of the entire UMA range when you install several
peripherals and/or when you try to maximize conventional memory. Consult the
manufacturer or the documentation to determine the memory range required by
each device driver, TSR program, and peripheral. Note the options for this
range's "starting" address (for example, C000, D000, or D800). Ensure that no
two devices (device drivers or TSR programs loaded high or peripherals) are
sharing any part of a range within this space.
- It may be necessary to use the EMM386.EXE "exclude range" switch (X=) in the
CONFIG.SYS file or the EMMexclude= parameter in the [386enh] section of the
SYSTEM.INI file. This option prevents software from accessing the specified
ranges in cases where the software does not recognize that the range is
already occupied.
Base I/O Address
----------------
Base I/O address (I/O port) is another "address" or path for system-
to-peripheral communication. The address table is 00H through FFFFH and should
not be confused with UMA mentioned above. A device's I/O port range has a base
address (for example, 300 or 320 or 3A0, and so forth). Each port address covers
a range (8, 16, or even 32 bytes); therefore, there exists a possibility of
overlap and conflict with devices whose starting addresses are close together.
Consult the manufacturer's documentation for range size and starting address
options. Ensure that each card has exclusive use of the range it occupies.
DMA Channel
-----------
Direct memory access (DMA) channel is a means for peripherals to directly access
RAM memory without requiring the services of the CPU. Many devices that move
large amounts of data (network cards, sound boards, hard disk drive controllers,
and so forth) take advantage of this feature to enhance overall system
performance and increase data throughput within certain applications.
The DMA channel is designated by a single number (0 through 7). Not all devices
use it. Some can use it as an option. Consult your manufacturer's documentation
for information on how, when, and why to use this option. Ensure each device has
exclusive use of its channel.
NOTE: DMA conflicts are somewhat less likely than UMA and base I/O address
conflicts. Fewer devices use it; and, in the case of a sound card for example,
the card's DMA channel may be in use only when the application using the card is
running.
Managing Complex Systems
------------------------
To help manage complex systems, make a chart like the one below, which documents
the current settings of each device. Keep this chart available and consult and
update it when you install more hardware.
Hardware IRQ Base I/O UMA DMA
-----------------------------------------------------------
Mouse Com 2 (3) COM 2(2F8h) N/A N/A
Device 1 5 300 D000 2
Device 2 x x n/a x
Device 3 x x x x
Additional query words: tshoot gpf 3.10 3.11
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Keywords :
Technology : kbAudDeveloper kbWin3xSearch kbWFWSearch kbZNotKeyword3 kbWin310 kbWin311
Version : WINDOWS:3.1,3.11
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