Asynchronous FIFO Pointer Offset for Clock Domain Crossing
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Solution Overview
Problem
Data transfer between clock domains in processors often results in meta-stability errors, which can be mitigated by meta-stability circuits or FIFOs, but these solutions increase latency and reduce processing efficiency.
Innovation Solution
A processor employs a FIFO controller that applies offset values to read and write pointers based on the frequency ratio between clock domains, allowing for faster data transfer while minimizing latency and maximizing bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If meta-stability circuits or asynchronous FIFOs are used to transfer data across clock domains, then data transfer reliability is improved, but latency increases and bandwidth decreases
Solution Approach 1:
The patent changes the parameter of pointer positioning by applying frequency-ratio-based offsets to read and write pointers. This allows the FIFO to operate with optimized timing parameters that reduce latency while maintaining data integrity across clock domains with different frequencies.
Solution Approach 2:
The patent implements dynamic pointer adjustment where the offsets are calculated based on the actual frequency ratio between clock domains. This dynamic approach allows the system to adapt to different frequency combinations, optimizing performance for each specific scenario rather than using fixed conservative timing.
2Reliability
If meta-stability circuits or asynchronous FIFOs are used to transfer data across clock domains, then data transfer reliability is improved, but processing efficiency deteriorates
Solution Approach 1:
By changing the timing parameters through frequency-ratio-based offsets, the system achieves faster data transfer rates. The offsets are calculated to minimize the time data spends in the FIFO, thereby improving processing efficiency while maintaining reliability.
Solution Approach 2:
The patent enables the FIFO to skip unnecessary waiting periods by using optimized pointer offsets. This allows data to rush through the buffer more quickly, improving throughput and processing efficiency without compromising data integrity.
3Productivity
If frequency ratio-based pointer offsets are applied, then bandwidth is maximized and latency is reduced, but system complexity increases
Solution Approach 1:
The patent uses feedback from the clock frequency monitoring to dynamically calculate and adjust pointer offsets. The system continuously monitors the frequency ratio between clock domains and adjusts the offsets accordingly, creating a self-regulating mechanism that maximizes bandwidth without requiring complex manual configuration.
Solution Approach 2:
The FIFO controller performs self-configuration by automatically calculating the appropriate offsets based on the detected frequency ratio. This self-service approach eliminates the need for external configuration or complex control logic, reducing system complexity while achieving optimized performance.
Data Source
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AI summary
A processor (100) applies offset values (155, 150) to read and write pointers (125, 115) to a first-in-first-out buffer (FIFO) (110) for data being transferred between clock domains (102, 104). The pointer offsets are based on a frequency ratio between the clock domains, and reduce latency while ensuring that data is not read by the receiving clock domain from an entry of the FIFO until after the data has been written to the entry, thereby reducing data transfer errors. The processor resets the pointer offset values in response to a change in clock frequency at one or both of the clock domains, allowing the processor to continue to accurately transfer data in response to clock frequency changes.