Troubleshooting - Lesson 64 The Motherboard/ DMA Failures Objectives: When you have completed this lesson, you will be able to recognize failures associated with the DMA controller on the motherboard. Discussion:

The DMA controller on modern motherboards is not really a separate integrated circuit but is part of the glue logic that makes up the operation of the modern motherboard. The DMA controller is part of a circuit on the motherboard know as the Application Specific Integrated Circuit or ASIC. As covered in an earlier lesson, the DMA controller is responsible for the transfer of data to and from the memory at extremely high speeds without the intervention of the CPU. Once a device or resource has requested a DMA transfer and the CPU has acknowledged the start of the DMA transfer activity, the CPU no longer plays any roll in the transfer of information to or from the memory while the DMA transfer is in progress. DMA failures are rare, and usually result in a replacement of the motherboard. DMA resource conflicts on the other hand are not rare, and are often the true cause of a DMA controller or DMA transfer system not functioning correctly.

Types of Failures: 1. Complete Failure: When a DMA controller fails, the most common observable symptom will be that of a dead computer. The DMA is necessary for all hard disk and floppy disk interaction and is tested during the POST. If the DMA controller is not functional, there is no way that the system will start. It should be noted that if the computer that is not working was a working machine in the past, and no one has attempted to perform any upgrade work or changed any settings, the DMA controller is most likely defective. If someone has installed new hardware, or has in any way changed settings on the computer, the DMA controller is most likely experiencing a resource

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Lesson 64 Troubleshooting - The Motherboard / DMA Failures

conflict, and as such the simplest method of determining whether or not the motherboard is defective would be to remove any unnecessary interface cards, and retest the system. 2. Intermittent Failures: This problem is most often associated directly with a resource conflict or an invalid setting in the system BIOS. Most intermittent problems can be traced to two devices being set to the same DMA request or (DREQ) setting, with the most common being an network interface card and a multimedia sound card occupying DREQ5. It is also possible on some of the modern BIOS settings to disable the settings for a given DREQ channel which my cause all different types of problems with the operation of the computer.

3. Device Driven Failures: Under the Windows Operating System, it is not possible for hardware to manipulate the computer directly, all low level communication must take place by way of a device driver. It is possible for a device driver to be incorrectly loaded, or not loaded at all, and as such will cause the system not to function properly.

Assignment: 1. The DMA controller on modern motherboards is really a separate integrated circuit.

a. True. b. False.

2. The DMA controller is responsible for the transfer of data two and from the memory at extremely high speeds without the intervention of the CPU.

a. True. b. False.

3. The most common symptom when a DMA controller fails would be that of a dead computer.

a. True. b. False.

4. If someone has installed new hardware or has in any way changed settings on the computer, the DMA controller is most likely experiencing a resource conflict.

a. True.

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Troubleshooting - The Motherboard / DMA Failures Lesson 64

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b. False. 5. The simplest method of determining whether or not the motherboard is defective would be to remove any unnecessary interface cards and retest the system.

a. True. b. False.

6. You get an intermittent failure with a resource conflict or an invalid setting in the system BIOS. Most problems can be traced to two devices being set to the same DMA request or setting.

a. True. b. False.