Verifying USB Interrupt Sharing Under Windows 2000/XP
To verify USB interrupt sharing status under Windows 2000 or Windows XP, from the Device Manager, choose View → Resources by Type, and expand the Interrupt request (IRQ) item, as shown in Figure 24-12.
Figure 24-12. Windows XP Device Manager showing that this system dedicates PCI interrupts 19 and 23 to the two USB HCIs
On recent motherboards, Windows 2000 and Windows XP typically assign a dedicated PCI interrupt above 15 to each device. On older motherboards, Windows 2000 and Windows XP typically assign a shared PCI interrupt to the HCI, as shown in Figure 24-13. Despite all assurances by hardware manufacturers and Microsoft that USB operates properly with a shared interrupt, that is frequently not true. If Windows has assigned a shared interrupt to USB, use the Device Manager to locate an unused interrupt, clear the Use Automatic Settings checkbox, and assign the unused interrupt to the HCI.
Figure 24-13. Windows 2000 Device Manager showing that this system shares one interrupt among the USB HCI and four other devices
On the system shown in Figure 24-13, Windows 2000 has assigned one shared PCI interrupt among the USB HCI, the SCSI host adapter, the video card, the network adapter, and the sound adapter. Surprisingly enough, all ...
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