Demystifying USB Protocol: Understanding Communication and Architecture

USB protocol

Overview

USB protocol stands for Universal Serial Bus and is the solution to transmit the data among multiple electronic devices like mouse, key board, speaker, etc..? by connecting them to the host computer or any other electronic device that acts as a host device.

The USB protocol was introduced in 1994 by some reputed companies like Compaq, Digital Equipment, IBM, Intel, Microsoft, and Northern Telecom, and is currently maintained and regulated by the USB Implementers Forum, or USB-IF.

The main intention behind conceptualizing this was to make a single interface that could be used across multiple devices to transmit the data and increase the data transmission speed among the connected devices.?

Over the years the USB protocol has undergone multiple revisions to increase the efficiency in transmission of the data among connected devices.

How does the USB Protocol communicate:

Generally, the USB Port consists of components such as the Host and the other peripheral devices. Those two components are connected through a tiered star topology. This topology can have multiple hubs between the connections to allow additional devices to be connected to the USB system. The host devices initiate the communication that happens over the USB bus. Typically the Host device can be any electronic device that can start the communication among its connected peripherals over the USB bus. Both host and peripheral devices have their respective driver software installed on the top of the hardware to make smooth communication over the USB protocol. The communication is successful only if both host and slave devices are in sync.?

Architectural Overview:

As we earlier saw the importance of USB protocol, Now let us discuss the architectural overview of it. The USB cable bus supports data transmission between the host and the other peripheral devices connected. The connected peripherals share the USB bandwidth through host-scheduled and token-based protocols.

Let's discuss more about the bolded sentence with a simple example,?

Imagine there are a bunch of your friends waiting to talk to you at your Party. but only one person is allowed to talk to you at a time. So, they each have a special token, like a ticket, that lets them take turns talking to you.?

In the USB, your computer is the "host" (like you at the party), and the devices you connect to it, like a mouse, keyboard, or printer, are your friends who want to talk to the computer.

Now, USB uses a system where the host computer schedules who gets to "talk" (send or receive data) at what time. Each device connected to the USB has its own turn to communicate, and it's determined by a token system.

So, just like your friends with their tokens, USB devices wait for their turn to send or receive data from the computer. This helps manage the flow of information and makes sure everything works smoothly, even if multiple devices are connected at the same time.

The bus allows some devices to be connected, disconnected, and configured while the host and other devices are in operation.?

USB system description:

There are three components all together comprising the USB system are?

1. USB interconnect
2. USB devices
3. USB Host

USB interconnect:

The USB interconnect is the channel to which the USB devices and the host are connected to exchange the data. This has some features such as:

• Bus Topology: This is the main channel between the host and devices to exchange the data.
• Inter-layer Relationships:? it defines the communication and the dependencies between the different layers of the USB protocol stack. The USB protocol stack is grouped into multiple layers and each layer serves a specific purpose in facilitating the communication and data exchange between the Host and peripheral devices. Those layers are as below:

1. Physical Layer:

This layer is responsible for the physical aspects of the USB connection. It includes the cable, connector, electrical signal, and transmission rate.?

1. Link Layer: This layer manages the transmission of data packets over the USB physical layer. It handles the data packet framing, error detection, and flow control. It works directly with the physical layer to make smooth data transfer over the USB connection.
2. Protocol Layer:? This layer plays a vital role in managing the devices connected over the USB connection. It includes the device enumeration, control transfer, and data transfer modes such as bulk, interrupts, and isochronous.
3. Device Class Layer: USB devices typically belong to specific device classes, such as Human Interface Devices (HID), Mass Storage Devices (MSD), Audio Devices, etc. The device class layer provides standardized protocols and interfaces for devices within each class, enabling interoperability and compatibility with the host. For each class, there are different protocols to serve differently.
4. Application Layer: generally It refers to the software applications that run on the Host to interact with the devices. It includes driver programming, middleware, and the user application that uses the USB interface to communicate with other devices.

• Data Flow Model: The way data flows in the system over the USB between master and slave devices.
• USB Schedule: The USB provides the common interconnect. Access to this is scheduled to support the isochronous data transfer.?

USB HOST:

Remember there is only one Host in any USB system. The USB interface to the host device is referred to as the host controller. Host controllers may be implemented in a combination of hardware and software.

USB Devices:

• Hubs which provide additional sockets to the USB
• Speakers, joysticks, mouse and keyboard etc.

By delving into the intricacies of the USB protocol outlined in this article, I hope you've gleaned valuable insights. As we journey through the complexities of USB communication, I look forward to expanding on these fundamentals and delving deeper into the intricacies of USB architecture in our upcoming discussion. If there's anything I can add to enhance your understanding, please feel free to let me know?

HARMAN Automotive HARMAN India KPIT Sparkle Continental Industry Capgemini Automotive 沃尔沃汽车 美光科技 伟世通