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Method of glitch-free termination of up-stream connectivity near the end of frame by USB hub/repeater

IP.com Disclosure Number: IPCOM000005066D
Publication Date: 2001-Aug-07
Document File: 1 page(s) / 22K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method of glitch-free termination of up-stream connectivity near the end of frame (EOF) by a USB hub/repeater when connectivity is established. Benefits include robust error recovery near EOF and compliance with Universal Serial Bus (USB) Specification 1.0.

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Method of glitch-free termination of up-stream connectivity near the end of frame by USB hub/repeater

Disclosed is a method of glitch-free termination of up-stream connectivity near the end of frame (EOF) by a USB hub/repeater when connectivity is established. Benefits include robust error recovery near EOF and compliance with Universal Serial Bus (USB) Specification 1.0.

Description

A USB hub/repeater propagates USB traffic between its downstream devices and the host. The hub provides fault tolerance by means of several error recovery features. The disclosed method enables bus traffic to be terminated gracefully when up-stream connectivity passes the EOF point. Specification 1.0 requires the hub/repeater to transmit an end of packet (EOP) upstream if up-stream connectivity is still established past the EOF point. The EOP is US13 signalling with two bits of single ended zero (SE0) followed by one bit of J state on the wire.

To meet the specification's requirement, a conventional hub/repeater performs as follows. First, it determines whether up-stream connectivity is still established at the EOF point. The hub synchronizes and samples the signals coming from the down-stream ports to determine if an artificial EOP must be issued. While performing the analysis, the repeater continues to propagate the USB signal upstream. A delay occurs between the data path that propagates the signal and the control logic that executes error recovery logic. As a result, the host may receive two SE0 instances, which resembles two EOPs and is invalid, and disable the hub.

To prevent this problem, the disclosed method utilizes a sequential logical procedure. The status of the root port is fed back to the EOF decision-making control software at the hub. An artificial EOP is transmitted if and only if the hub/repeater is currently transmitting SE0 on its root port or propagating a data packet. Data path logic remains the same as previously described. The problem of the race between propagated EOP signal and the generated EOP signal by the hub/repeater on its root port is eliminated.

Benefits

The disclosed method is insensitive to the external and internal environments. Implementation is fully synthesizable without any special consideration to the timing of up-stream bus traffic or to internal logic circuit performance. Conventional solutions require careful adjustment of the circuit performance to mask out the glitch. Glitch-free termination and successful fault recovery near EOF successfully occur and meet all requirements of Universal Serial Bus (USB) Specification 1.0.

Disclosed anonymously