If a USB hub connects multiple devices, how many IRQs are required for the devices?

When a USB hub is used to connect multiple USB devices, all of those connected devices share a single IRQ (Interrupt Request Line) assigned to the hub itself. The USB architecture allows for this efficient management because the hub effectively manages the communication between the host computer and the connected devices. Each device does not require its own dedicated IRQ; instead, the hub multiplexes the data to and from the host, using one IRQ for all the traffic.

This design simplifies the interrupt management, which is particularly beneficial in systems with limited IRQ resources. As a result, only one IRQ is needed for all devices connected through a single USB hub, illustrating the USB protocol's efficiency in handling multiple devices.