USB Transaction Translator SOF Timer Synchronization
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Solution Overview
Problem
USB 3.0 transaction translators face synchronization issues between host and device sides due to differing clock sources and micro-frame timing mismatches, leading to access conflicts and inefficient bandwidth usage during isochronous transactions with USB 2.0 devices.
Innovation Solution
A USB 3.0 transaction translator with a device interface, host interface, buffers, and a controller that synchronizes start-of-frame packets with isochronous timestamp packets by delaying their sending based on received timestamp information, using a start-of-frame counter and timer to ensure simultaneous packet transmission and adjust data transfer periods for improved synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the U3TT sends SOF packets periodically to announce micro-frame time, then the device can maintain timing information, but the host and device may access the same buffer at the same time causing access conflicts
Solution Approach 1:
The patent applies preliminary action by having the U3TT delay the sending of SOF packets until after the host has finished reading data from the buffer. The controller waits for the host to complete its read operation before the U3TT transmits the SOF packet, thereby preventing access conflicts before they occur. This timing adjustment ensures that the buffer is not accessed simultaneously by both host and device.
2Adaptability or versatility
If the host and U3TT use different clock sources, then each side can operate independently, but a period difference accumulates causing synchronization problems
Solution Approach 1:
The patent implements feedback by having the U3TT receive isochronous timestamp packets (ITP) from the host and use this timing information to adjust the sending time of SOF packets. The controller calculates the time difference based on the ITP and delays SOF packet transmission accordingly, creating a feedback loop that continuously compensates for clock source differences and maintains synchronization.
3Productivity
If the U3TT uses buffers to pre-fetch data, then bandwidth usage is improved, but the complexity of coordinating buffer access between host and device increases
Solution Approach 1:
The patent uses the SOF packet as an intermediary signal to coordinate buffer access between the host and device. The SOF packet serves as a timing reference that the host uses to determine when it is safe to read from the buffer. By synchronizing buffer access around the SOF packet transmission, the system manages the complexity of coordinated access while maintaining high bandwidth usage through pre-fetching.
Data Source
AI summary
A universal serial bus (USB) transaction translator is provided along with a micro-frame synchronization method. A device interface is coupled to a device via a device bus, and a host interface is coupled to a host via a host bus. At least two buffers are configured to store data. A controller stores the data in the buffers alternately. A start-of-frame (SOF) counter is used to count the SOF packets, with the counting value of the SOF counter being compared to a predefined value. Specifically, the controller resets a SOF timer for sending the SOF packet when the counting value achieves or exceeds the predefined value, such that the SOF packet and an isochronous timestamp packet (ITP) from the host are sent at the same time. Further, the controller delays the sending of the SOF packet for a period of time according to the ITP from the host.