Processor Wrapper Registers via Local Bypass Network
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Solution Overview
Problem
Conventional RISC-based ISAs, such as RISC-V, provide an insufficient number of control and status registers (CSRs) for large data processing systems, which are not easily accessible by firmware, hardware, and co-processors, leading to access latency issues when extended in memory mapped I/O.
Innovation Solution
Implement a local bypass network to route traffic directly to a collection of registers, including wrapper registers, in close proximity to processors, bypassing the main system interconnect and memory mapped I/O, allowing low-latency access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the set of CSRs is extended using memory mapped I/O, then the number of accessible registers is increased, but access latency increases significantly
Solution Approach 1:
The patent divides the register access path into two segments: a local fast path for CSR accesses and a remote slow path for other memory-mapped I/O accesses. The local bypass network creates a dedicated segment for register access that is physically separated from the main interconnect fabric, allowing CSR accesses to bypass the congested interconnect and achieve low-latency access while maintaining extended CSR capacity through memory-mapped I/O.
Solution Approach 2:
The patent introduces a local bypass network as an intermediary component between the processor and the memory-mapped I/O space. This intermediary intercepts CSR access requests before they reach the main interconnect fabric and routes them through a dedicated low-latency path to the register file, effectively mediating between the processor and extended registers to eliminate the latency penalty of memory-mapped I/O.
2Ease of operation
If specialized CSR instructions are used to access CSRs, then access to control and status registers is enabled, but accessibility by firmware and hardware is restricted
Solution Approach 1:
The patent implements a universal access mechanism through the local bypass network that allows multiple types of accessors (processor, firmware, hardware, co-processors) to access CSRs through a common interface. The network monitors address traffic and automatically routes requests to the appropriate destination based on address decoding, eliminating the need for specialized instructions and enabling universal accessibility while maintaining the original CSR functionality.
3Adaptability or versatility
If CSRs are made accessible by multiple processors, then system-wide accessibility is improved, but access latency increases due to interconnect traffic
Solution Approach 1:
The patent applies local quality by providing each processor with a local bypass network that gives it direct, low-latency access to its own CSR set. When a processor needs to access another processor's CSR, the request is routed through the interconnect fabric with higher latency. This creates a quality gradient where local accesses are fast and remote accesses are slower but still functional, optimizing the common case while maintaining system-wide accessibility.
Data Source
AI summary
Systems and techniques for accessing a set of registers associated with a processor via a local bypass network associated with the processor are described. An example technique includes obtaining traffic comprising an interconnect fabric address. The traffic is diverted to a set of registers associated with a processor in a computing system upon determining that one or more predefined bits of the interconnect fabric address satisfy a predetermined condition.