Serial Link Buffer Fill Compensation via SOP Timing Characters
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Solution Overview
Problem
Existing data communication systems face inefficiencies in high-speed serial links due to costly clock accuracy requirements and bandwidth consumption from in-band timing compensation methods, which restrict the use of inexpensive clock sources and hinder design flexibility.
Innovation Solution
Implementing a bidirectional serial link system where near-end and far-end transmitters adjust data transmission rates based on real-time buffer fill level indications, eliminating the need for precise clock sources and reducing bandwidth overhead by using SOP character sequences to convey buffer fill information within PDUs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If in-band insertion of idle characters is used for timing compensation, then receiver buffer fill rate compensation is achieved, but link bandwidth is consumed as overhead
Solution Approach 1:
The patent makes SOP characters serve dual purposes: they delimit PDUs and simultaneously convey receiver buffer fill level information to the transmitter. This eliminates the need for separate idle characters dedicated solely to timing compensation, thereby recovering link bandwidth while maintaining timing compensation functionality
Solution Approach 2:
The patent combines the PDU delineation function and the timing compensation function into a single mechanism by encoding buffer fill level information within the SOP characters themselves, merging what were previously separate functions into one integrated system
2Reliability
If fixed interval transmission of special timing characters is used, then receiver can compensate buffer fill rate, but accurate reference clock is required
Solution Approach 1:
The patent transitions from a static, fixed-interval timing character transmission scheme to a dynamic scheme where SOP characters are transmitted continuously as part of normal data flow. The timing information is embedded in the ongoing data stream rather than relying on periodic inserts, allowing the system to adapt to varying buffer conditions without requiring precise periodic clocking
Solution Approach 2:
The patent implements a feedback mechanism where the receiver monitors its buffer fill level and communicates this information back to the transmitter through the SOP characters. The transmitter uses this feedback to dynamically adjust its transmission rate, creating a closed-loop control system that compensates for timing discrepancies without requiring highly accurate reference clocks
3Reliability
If idle characters are inserted for timing compensation, then transmitter and receiver timing discrepancies are addressed, but design freedom in clock source selection is restricted
Solution Approach 1:
The continuous feedback mechanism embedded in the data stream allows timing compensation to occur dynamically regardless of the clock source characteristics. This enables the use of lower-cost, less accurate clock sources while maintaining synchronization through active adjustment based on real-time buffer status information
Data Source
AI summary
Embodiments of the invention provide improved timing compensation for a bidirectional serial link in order to relax accuracy requirements of clock sources used for the link. When forming a Protocol Data Unit (PDU) for transmission over the link, fill levels of receiver buffers at either ends of the link are used to determine a particular type of start of PDU (SOP) character sequence to use. When a given type of SOP character sequence is present in a PDU received at one end of the link, a next PDU to be transmitted from the same end of the link is delayed by a predetermined amount of time to allow the receiver buffer at the other end of the link to decrease its fill level before receiving the next PDU.