PRB: Operating System Does Not Recognize Disabled or Not Present IDE Secondary Channel (811791)

SYMPTOMS

When you run Windows XP on a computer that is using National Semiconductor GX2/CS5535 Integrated Device Electronics (IDE) controller chipset, the operating system does not recognize that the secondary channel is absent. As a result, Device Manager continues to report that the second channel is enabled and an interrupt resource is allocated to the channel.

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

CAUSE

Windows XP does not completely support the National Semiconductor GX2/CS5535 chipset and does not correctly query the status of the IDE channels. Therefore, by default, Windows XP sets the status of both channels to Enabled. This behavior does not affect the functionality of the chipset and the chipset works correctly. However, the resources will be unnecessarily allocated for the secondary channel.

RESOLUTION

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

IMPORTANT: follow the procedure to resolve this issue only if your computer has a NSC CS5535 IDE chipset.

You can verify that you are using the listed chipset by using the Regedit.exe tool: under the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\PCI key, look for PCI\VEN_100B&DEV_002D&SUBSYS_002D100B&REV_00.

To resolve this issue, follow these steps:

Start Registry Editor (Regedit.exe or Regedt32.exe).
Locate and then click the registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E96A-E325-11CE-BFC1-08002BE10318}
Under the instance that corresponds to the NSC IDE controller entry, add the following keys.
Keyword Type DWORD
MasterOnConfigOffset REG_DWORD 0x44
MasterOnMask REG_DWORD 0x10
SlaveOnConfigOffset REG_DWORD 0x44
SlaveOnMask REG_DWORD 0x01
Note: it is a good idea to verify the registry after editing, because any mistyping can result in an unbootable image.
Restart the computer.

You can expect the operating system to display the settings of the IDE channels in Device Manager. If any of the channels have been disabled, the resources that are being used by that channel are released so that they can be used by other devices.