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Arithmetic Logic Unit

Concept WIKI v1 · 5/25/2026

In the provided Y86-64 microprocessor evidence, the arithmetic logic unit (ALU) is an execute-stage functional block that operates on register values, immediate instruction data, and numeric constants. It can perform addition or the arithmetic/logical operation selected by an instruction, producing an ALU result used by later memory and write-back activity.

Overview

An Arithmetic Logic Unit (ALU) is identified in the provided Y86-64 processor material as the hardware block responsible for arithmetic and logical operations. In the SEQ sequential reference implementation, the ALU is part of the execute-stage data path and is controlled along with other processor blocks whose detailed functionality is described in HCL, a language for describing control logic. [ALU role in SEQ]

Inputs and operations

During a SEQ clock cycle, the processor fetches instruction bytes, computes the next sequential instruction address, reads up to two register-file values, and then uses the ALU. The ALU operates on some combination of:

  • values read from the register file,
  • immediate data from the instruction, and
  • numeric constants. [ALU operands]

The ALU can perform either addition or the operation requested by an arithmetic or logical instruction. [ALU operations]

Place in the processor flow

In the SEQ hardware structure, the ALU appears in the execute stage with ALU input paths labeled ALU A and ALU B, an ALU fun. control input, and an output valE. The surrounding flow described in the evidence places the ALU after register reads and before memory access and write-back: a value may be read from or written to data memory, and some combination of the memory result and ALU result is written back to the registers. [ALU position in flow]

Relationship to Y86-64 implementations

The evidence describes SEQ as a sequential reference version and PIPE as a five-stage pipelined implementation of the Y86-64 instruction set. PIPE partitions computation into similar stages and uses the same set of functional blocks as SEQ, while adding pipeline registers so that up to five instructions can flow through the pipeline simultaneously. Therefore, within the provided evidence, the ALU is a functional block used in the Y86-64 processor implementations discussed. [Y86-64 implementation context]

LINKED ENTITIES

1 links
Y86-64 CONTAINS

CITATIONS

5 sources
5 citations
[1] ALU role in SEQ Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5
[2] ALU operands Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5
[3] ALU operations Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5
[4] ALU position in flow Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5
[5] Y86-64 implementation context Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5