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cdrom3.gif Introduction To DMA
cdrom3.gif IRQ’s (Interrupt Request Level)
cdrom3.gif DMA (Direct Memory Access) Channels
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DMA Settings, IRQ's, and Jumper Configurations Related To Sound Cards

Introduction To DMA

Expansion cards have to request the CPU to send the same information over and over again. To avoid this repetition and resulting bottlenecks in a system the processor communicates with a card through Direct Memory Access (DMA) channels. DMA is a technology that defines how data travels through different parts of the PC.

Base memory addresses are often referred to as Input/Output (I/O) ports. CPU’s respond to an Interrupt Request (IRQ) and as a result, a different route can be configured and communicated through the system, thus enabling the processor to complete its tasks faster.

There are a varying number of I/O ports available to communiate with a PC. These ports can also be refferred to as "memory addresses" and typically take the format 02E8 or 03E8. These addresses are specific parts in memory in which the processor and sound card communicate with each other to get things done.


DMA (Direct Memory Access) Channels

DMA channels permit a direct pathway for hardware devices to communicate with other peripherals in a computer without any CPU intervention. Systems utilizing DMA can transfer data at a much faster speed than non-DMA based systems. Older motherboards and hardware devices required the use of a seperate card and device drivers to take full advantage of DMA benefits. Newer parts and operating systems (such as Windows XP Media Centre Edition) have built in support for DMA, thus requiring no additional hardware or software support.

Sound cards, floppy drives, and some older style hard drives employ DMA protocols. The following table illustrates the most common types of devices that take advantage of DMA protocols.

IRQ’s (Interrupt Request Level)

IRQ's are basically “stop and do this” messages given to the CPU when a device calls on the CPU to complete a task. For example, each time you press the Enter key on the keyboard, the keyboard controller sends an IRQ instruction to the CPU demanding it to carry out that function.

Each component in a computer must be configured to use its own communicaton line or IRQ setting for the successful transmission of data.

Some hardware devices share interrupt requests peacefully within a Windows system. If two devices are configured to use the same interrupt request conflicts will occur often resulting in neither of the hardware devices working.

The following table summarizes the most popular IRQ settings and the devices they are in charge of.

IRQ #

Typical Device(s) Controlled:

0 System Timer
1 Keyboard
2 Some video cards
3 COM2, COM4
4 COM1, COM3
5 Sound Card
6 Floppy Drive Controller
7 LPT1 (Printer Port)
8 CMOS Clock
9 Redirected to COM2, Power Management / ACPI Controller Function.
10 Serial Bus Controller
11 Display Controller
12 Network Controller
13 Math Coprocessor
14 Hard drive controller
15 Free
16 USB Host Controller
18 Hard Disk IDE Controller or USB Host Controller
21

Wireless Network Controller

22 Multimedia Controller, Television Tuner Card, or Video Capture Device
23 Audio Controller or USB Enhanced Host Controller
Table 1.1 - Various IRQ settings in a PC and the devices they control.

Many operating systems have utilities that allow you to check the IRQ settings for your computer. If you are running DOS, MSD (Microsoft Diagnostics) is the program you need to use to view information about the configuration of your computer. In Windows XP the System Information tool can provide you with extensive information about the hardware in your computer.


 
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