Instruction Execution Operand Field Reinterpretation
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Solution Overview
Problem
Reduced instruction set computing (RISC) processors face inefficiencies due to limited bit-width, particularly with 16-bit instruction sets, which restrict the number of bits available for expressing operands, necessitating the use of prefixes to extend operand fields but not reducing overall instruction set size effectively.
Innovation Solution
A method and processor architecture that differentiate between integral and non-integral instructions, where the operand field of a second instruction is interpreted to provide values for a first instruction or indicate look-up table entries, allowing for more efficient information conveyance by combining bits from both instructions or using look-up tables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If prefixes are used to extend operand fields in 16-bit instruction sets, then the number of addressable registers is increased, but the overall instruction set size is not reduced
Solution Approach 1:
The patent merges the prefix instruction and main instruction into a single integrated instruction format. The operand field of the main instruction is reinterpreted to provide values for the prefix when they are integral, eliminating the need for separate prefix bits and reducing overall instruction size while maintaining extended operand capability.
Solution Approach 2:
Instead of using prefixes to extend operands (adding bits), the patent inverts the approach by reinterpreting the main instruction's operand field to provide values for the prefix when integral. This inversion reduces the total bit requirement while achieving the same extension effect.
2Adaptability or versatility
If 32-bit instruction sets are used, then flexibility in expressing instructions and operands is improved, but code size increases
Solution Approach 1:
The patent applies partial action by conditionally interpreting the operand field - only when the first instruction is integral with the second instruction does the operand field provide values for the first instruction. Otherwise, it indicates look-up table entries. This selective approach maintains flexibility while reducing average code size.
Solution Approach 2:
The patent introduces a look-up table as an intermediary mechanism. When instructions are not integral, the operand field indexes into the look-up table to retrieve additional information, reducing the need to encode all information directly in the instruction stream and thereby reducing code size.
3Productivity
If the operand field is interpreted to provide values for integral instructions, then information conveyance efficiency is improved, but instruction decoding complexity increases
Solution Approach 1:
The patent applies preliminary action by first determining whether the first instruction is integral with the second instruction before interpreting the operand field. This preliminary determination simplifies the decoding logic by creating clear conditional branches rather than requiring complex simultaneous interpretations.
Solution Approach 2:
The patent changes the interpretation parameter of the operand field based on the integral relationship determination. When integral, the operand field provides values for the first instruction; when not integral, it indexes the look-up table. This parameter change approach maintains simple decoding logic while achieving efficient information conveyance.
Data Source
AI summary
A method of executing an instruction set including a first instruction and a second instruction, includes reading the first instruction; determining whether the first instruction is an instruction which is integral with the second instruction; reading the second instruction; if the first instruction is integral with the second instruction, interpreting the operand field of the second instruction to indicate at least one value to be used in conjunction with at least one bit of the first instruction; and if the first instruction is not integral with the second instruction, interpreting the operand field of the second instruction to indicate an entry of a look-up table.