To communicate with USB devices, a computer needs hardware and software that support the USB host function. The hardware consists of a USB host controller and a root hub with one or more USB ports. The software support is typically an operating system that enables device drivers to communicate with lower-level drivers that access the USB hardware.
A typical PC has one or more hardware host controllers that each support multiple ports. The host is in charge of the bus. The host has to know what devices are on the bus and the capabilities of each device. The host must also do its best to ensure that all devices on the bus can send and receive data as needed. A bus may have many devices, each with different requirements, all wanting to transfer data at the same time. The host’s job isn’t trivial.
Fortunately, the host-controller hardware and drivers in Windows and other operating systems do much of the work of managing the bus. Each device attached to the host must have an assigned device driver that enables applications to communicate with the device. System-level software components manage communications between the device driver and the host controller and root hub.
Applications don’t have to know the hardware-specific details of communicating with devices. All the application has to do is send and receive data using standard operating-system functions or other software components. Often the application doesn’t have to know or care whether the device uses USB or another interface. The host performs each of the tasks described below.
Tags: Another, interface, The Device Uses, USB
