USB Extension Port Device Endpoint Table Buffer Management
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Solution Overview
Problem
The existing USB specifications limit SuperSpeed connections to a maximum cable length of 3 meters, restricting the distance between a host device and a USB device, necessitating new techniques to extend SuperSpeed USB connections beyond this limit while maintaining compliance with USB standards.
Innovation Solution
A USB extension system comprising upstream and downstream facing port devices that use an extension medium to increase the distance between host and USB devices, hiding the extension medium from the host and USB devices and compensating for latency, allowing seamless communication through a protocol engine, buffers, and an endpoint table to manage endpoint activity and buffer allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If USB cable length is extended beyond 3 meters, then connection distance is improved, but signal integrity and timing compliance deteriorate
Solution Approach 1:
The patent introduces extension devices (ED) as intermediary components between the host and USB devices. These EDs act as protocol translators that receive USB packets from the host, process them through protocol translation, and forward them to the USB device. This intermediary approach allows the system to maintain USB protocol compliance while extending the physical connection distance beyond the standard 3-meter limit, as the ED compensates for signal degradation and timing issues over longer distances.
Solution Approach 2:
The patent segments the USB connection into multiple sections: host device, extension device(s), and USB device. Instead of a single direct connection, the system divides the communication path into discrete segments with defined interfaces. Each segment maintains standard USB protocol compliance, while the overall system achieves extended reach. The extension device segments the timing and protocol handling, allowing each segment to operate within standard parameters while the aggregate connection exceeds traditional length limits.
2Length of stationary object
If extension medium is introduced to increase distance, then connection distance is improved, but system complexity increases
Solution Approach 1:
The extension device serves as a smart intermediary that manages the complexity of the extended connection. It implements the USB extension protocol, handles packet translation, and manages timing synchronization between the host and USB devices. By centralizing these complex functions in the extension device, the host and USB devices can remain simple standard USB components, thus managing overall system complexity while achieving extended connection distances.
Solution Approach 2:
The extension device creates virtual copies of USB endpoints and maintains endpoint tables that mirror the actual USB device endpoints. This copying mechanism allows the host to interact with virtual endpoint representations while the extension device translates these to real endpoint addresses. The endpoint table acts as a mapping copy that simplifies the complexity of managing extended connections by providing a straightforward interface that abstracts the physical extension infrastructure.
3Reliability
If endpoint table is used to manage active endpoints, then communication reliability is improved, but processing overhead increases
Solution Approach 1:
The extension device performs preliminary actions by pre-establishing the endpoint table with all possible endpoint mappings before actual USB communication begins. During USB device enumeration, the extension device proactively creates endpoint table entries and assigns virtual endpoint addresses. This preliminary setup eliminates the need for complex real-time lookups and decision-making during data transmission, as the mapping relationships are already established and cached, thus reducing processing overhead while maintaining communication reliability.
Data Source
AI summary
A port device for use in a USB extension environment that couples a host device to one or more USB devices is provided. The port device includes a USB physical layer interface configured to be coupled to a USB device, a host device, or a USB hub device; a remote interface configured to be coupled to an extension medium; and an endpoint table. The port device includes logic that, in response to execution by the port device, causes the port device to perform actions comprising: receiving a first USB message addressed to a first endpoint; in response to determining that the endpoint table indicates that the first endpoint is active, providing the first USB message for transmission to the first endpoint; and in response to determining that the endpoint table indicates that the first endpoint is inactive, providing a synthetic USB message for transmission to the host device.