Overlapped Immediate Register Field Specifying Instruction Encoding
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Solution Overview
Problem
The challenge in designing an instruction set architecture (ISA) is to determine which processing operations to support within a limited instruction encoding space, as increasing bit width increases hardware and power costs, leading to insufficient opcode space to represent all desired data processing operations.
Innovation Solution
The implementation of an overlapped-immediate/register-field-specifying (OIRFS) instruction that shares bits between the immediate value and register specifier fields, allowing the instruction decoder to use a selected register as a source or destination based on the immediate value, and decoding shared bits as either part of the immediate value or register specifier, thereby freeing up encoding space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the instruction bit width is increased to represent more data processing operations, then the opcode space is improved, but the circuit area and power consumption increase
Solution Approach 1:
The patent merges the immediate value field and register specifier field into a single overlapped field. The same bits are used to encode both the immediate value and the register specifier, depending on the opcode. This consolidation reduces the total number of bits required in the instruction encoding, freeing up space for additional opcode bits without increasing instruction width, thereby resolving the contradiction between opcode space and circuit area.
2Adaptability or versatility
If the instruction bit width is increased to represent more data processing operations, then the opcode space is improved, but the power consumption increases
Solution Approach 1:
By consolidating the immediate value and register specifier into an overlapped field, the patent reduces the total bit width required for instruction encoding. This reduction in bit width directly decreases the power consumption associated with storing and transferring instructions across the processor, while still providing sufficient opcode space to represent a diverse set of data processing operations.
3Adaptability or versatility
If encoding efficiency is improved to save bits, then the number of processing operations is improved, but the instruction encoding complexity increases
Solution Approach 1:
The patent employs dynamic field interpretation where the meaning of bits in the overlapped immediate/register field changes based on the opcode. The instruction decoder dynamically determines whether the overlapped field should be interpreted as an immediate value, a register specifier, or a combination thereof, based on the specific opcode being executed. This dynamic approach enables efficient bit usage while managing encoding complexity through context-dependent interpretation.
Data Source
AI summary
An apparatus comprises: processing circuitry, an instruction decoder, and registers. In response to an overlapped-immediate/register-field-specifying (OIRFS) instruction comprising an opcode field specifying an OIRFS-indicating opcode value, and an overlapped immediate/register field specifying an immediate value and a register specifier, the instruction decoder controls the processing circuitry to use a selected register of the plurality of registers corresponding to the register specifier as a source register or destination register when performing a processing operation depending on the immediate value. The overlapped immediate/register field includes at least one shared bit decoded as part of the immediate value for at least one encoding of the OIRFS instruction and decoded as part of the register specifier for at least one encoding of the OIRFS instruction.