Source Asynchronous Signaling Protocol for High Latency Interconnects
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Solution Overview
Problem
As integrated circuit technology scales down, wire latency increases due to increased resistance in smaller wires, leading to significant communication delays, which existing methods have been unable to effectively mitigate despite advancements in materials and designs.
Innovation Solution
The implementation of Source Asynchronous Signaling (SAS) protocol, which decouples request and acknowledgment handshaking signals, allowing multiple operations without intervening signals, thereby reducing the impact of wire latency on communication bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wire cross-sectional area is reduced to increase communication link density, then the number of communication links increases, but wire resistance increases and communication latency increases
Solution Approach 1:
The communication channel is divided into multiple segments with pipeline stages inserted between them. Each pipeline stage includes storage elements that hold data while control signals traverse the wire. This segmentation allows the physical wire to be longer without proportionally increasing latency impact, as data waiting in pipeline stages is not blocked by wire propagation delay.
Solution Approach 2:
Data is pre-loaded into pipeline storage elements before the control signal (handshake) completes its traversal of the wire. The pipeline stages are prepared in advance with data, so when the control signal arrives, the data is already positioned and ready for transfer, eliminating the need to wait for wire propagation before data is available.
2Reliability
If traditional handshake protocols are used, then flow control is maintained, but wire latency limits communication bandwidth
Solution Approach 1:
The handshake protocol is segmented into control signals that traverse the wire separately from data. Control signals initiate and acknowledge data transfers without requiring the data to travel the entire wire distance during the handshake process. Data resides in pipeline stages locally, while control signals communicate transfer status across the wire.
Solution Approach 2:
Pipeline storage elements act as intermediaries between data sources and destinations. These storage elements buffer data and decouple the data path from the control path, allowing control handshakes to proceed independently of data wire traversal time. The intermediaries absorb the latency mismatch between fast local data access and slower long-distance control signaling.
Data Source
AI summary
Technology for asynchronous communication including a wired channel, a sender controller, and a receiver controller is disclosed. The sender controller can be configured to send multiple request signals up to a predefined limit on the output request port paired with multiple data blocks sent on the data before receiving an acknowledgment signal on the output acknowledge port. At least one combination of any of the input channel, the sender controller, the output channel, and the receiver controller can be configured to operate within at least one time constraint to avoid stalling an asynchronous flow control.