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Today, I will talk to you about what the USB3.0 protocol specifications are, which may not be well understood by many people. In order to make you understand better, the editor has summarized the following contents for you. I hope you can get something according to this article.

Comparison of characteristics between USB3.0 and USB2.0

3.2 overspeed structure

The overspeed bus is a hierarchical communication structure, as shown in the following figure:

Protocol layer:

The protocol layer defines end-to-end communication rules between hosts and devices. The overspeed protocol provides the exchange of application data information between the host and the device endpoint (endpoint). This communication relationship is called pipe.

It is a host-oriented protocol, which means that the host decides when to transfer application data between the host and the device. The device can initiate an asynchronous request for service to the host through a specific endpoint, so it is not a polling protocol (USB2.0 is a polling protocol).

Data can be transmitted continuously in bursts to improve bus efficiency.

For some transport types (block transport), the protocol provides flow control support.

SS devices can be sent asynchronously to notify the host that the functional state of the device has changed. Instead of polling. The device endpoint can notify the host to send and receive data through the "ready" packet (ERDY TP) sent by the device asynchronously. For the "ready" notification, the host will add a pipeline if there is a valid data transmission or cache to receive data.

The host sends a special header (ITP) containing the host timestamp to the bus, which can be used to keep the device and the host synchronized, if necessary.

Overspeed USB Power Management:

The key points of link power management are:

The device sends an asynchronous "ready" notification to the host

The packet has a routing path, which allows links that are not involved in data communication to enter or remain in a low power state.

If the packet is sent to a port in a low power state, the port switches to exit the low power state and indicates that this is a switching event.

Equipment:

Speeding needs to support USB2.0 's default control pipe.

HUB device:

Because USB3.0 is backward compatible with USB2.0, to support the USB3.0 dual-bus structure, USB3.0 HUB is logically a combination of two HUB: a USB2.0 HUB and a USB3.0 HUB. The power supply and ground wire connected to the upstream port are shared.

The hub participates in an end-to-end protocol and does the following:

Route the output packet to the downstream port.

Input packet mixed transfer to upstream port

Broadcast timestamp packets (ITP) to all downstream ports when not in low power state

When a packet is detected in a low-power port, the hub converts the target port to exit the low-power state, notifying the host and device (in-band) that the packet has encountered a port in the low-power state.

Host (Hosts):

A USB3.0 host is interconnected with USB devices through a master controller. In order to support USB3.0 dual-bus structure, the USB3.0 master controller must include USB3.0 and USB2.0 parts, so that it can manage the control, state and information exchange between hosts and devices on each bus at the same time.

The host contains several root downlink ports to achieve overspeed USB and USB2.0, and the host uses these ports:

Detect the connection and removal of USB devices

Manage control flow between hosts and devices

Manage data flow between hosts and devices

Collect status and activity statistics

Supply power to connected devices

USB system software inherits the structure of USB2.0, including:

Device enumeration and configuration

Planning for periodic and asynchronous data transfer

Equipment and functional power management

Device and bus management information.

Data flow model:

Overspeed USB integrates USB2.0 's data flow model, including:

The exchange of data and control between the host and the device is carried out through the pipeline (pipe), and the data transfer is carried out between the host software and the designated device endpoint.

A device can have more than one active pipeline, and there are two types of pipes: streaming pipes (data) and message pipes (control). Streaming pipes do not have USB2.0-defined structures, and message pipes have specified structures (requested structures). Pipes are associated with data bandwidth, transmission type (described below), and endpoint properties, such as transmission direction and buffer size.

Most pipes do not exist until the device is configured by the system software, but when the device is powered on in the default state, a message pipeline, the default control pipe, always exists. Provides configuration, status and control information for access devices.

A pipe supports one of the four transport types defined by USB2.0 (pipe and endpoint properties are the same).

The mass transfer type (bulk) is extended in overspeed, called stream. Streaming provides support for multiplexing multiple independent logical data streams in a standard block transmission pipeline at the protocol level.

After reading the above, do you have any further understanding of the USB3.0 protocol specification? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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