Processor Compression Buffer for VLIW Instruction Fetch Latency
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Solution Overview
Problem
The VLIW machine faces bottlenecks in clock speed due to memory latency issues caused by the need to read stop bits from memory, which lengthens clock cycles and may require additional cycles for instruction fetch, leading to inefficient processing.
Innovation Solution
A processor with a compression buffer and instruction decompression unit that decompresses instruction bundles using previously stored compression codes, allowing for parallel processing and reducing memory access latency by buffering and synchronizing compression codes across clock cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stop bits are read from memory to determine NOP instructions, then instruction execution control is achieved, but memory latency increases and clock speed decreases
Solution Approach 1:
The patent pre-calculates and stores compression codes for instruction bundles before execution. The compression code generation unit creates these codes in advance based on the instruction bundle content, so that during execution, the processor can directly use the pre-generated compression codes without needing to read stop bits from memory during the critical execution path, thereby eliminating memory latency delays
Solution Approach 2:
The patent introduces compression codes as an intermediary data structure between the instruction bundle and the execution control logic. Instead of directly reading stop bits from memory to control execution, the system uses compression codes that encode the same control information in a more efficient format that can be processed without memory access delays
2Reliability
If stop bits are read from memory during each instruction fetch, then NOP instructions are correctly identified, but additional clock cycles are required
Solution Approach 1:
The compression codes are generated in advance and stored with the instruction bundles. These pre-generated codes contain all the necessary information for identifying NOP instructions and controlling execution flow, eliminating the need for additional memory reads during the instruction fetch cycle
3Loss of time
If compression codes are fetched and stored in a compression buffer, then memory latency is reduced, but additional buffer hardware is required
Solution Approach 1:
The patent divides the instruction bundle processing into segments: the instruction bundle itself and the associated compression code. The compression code is stored in a dedicated compression buffer that is tightly integrated with the instruction fetch logic, allowing parallel processing and eliminating the need for sequential memory accesses
Data Source
AI summary
The description relates to an instruction fetch technology of a processor that processes a plurality of instructions in parallel. The processor exploits the use of a compression code fetched during a previous clock cycle when fetching compressed instructions from a program memory and creating an instruction bundle consisting of a sequence of instructions to be processed in parallel. A compression buffer is interposed between the program memory and an instruction decompression unit, such that a compression code read in a previous clock cycle is ready at the beginning of a decompression cycle of the subsequent instruction bundle thereby avoiding a delay due to memory read latency.