4.1 Computer Architecture RISC-V Chapter

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Questions and Answers

What role does the program counter (PC) play in the RISC-V instruction execution process?

The program counter provides the instruction address to the instruction memory, starting the process of fetching the instruction.

How are register operands specified in a RISC-V instruction?

What happens to the ALU result when an arithmetic-logical instruction is executed?

The result from the ALU is written back to a register.

In a load or store operation, what does the ALU result represent?

The ALU result serves as the address for either loading a value from memory into the registers or storing a value from the registers into memory. Signup and view all the answers

How does the RISC-V architecture determine the next instruction address when executing a branch?

The next instruction address is determined by the ALU output, which can either sum the PC and branch offset or increment the PC by four. Signup and view all the answers

What are the two essential steps that occur for every RISC-V instruction implementation?

Fetch the instruction from memory using the program counter (PC) and read one or two registers based on instruction fields. Signup and view all the answers

How does the subset of RISC-V instructions affect the design of the datapath?

The subset influences the complexity and organization of the datapath, focusing on essential operations while omitting advanced features like shifting and multiplication. Signup and view all the answers

Explain the significance of the instruction set architecture in the implementation of RISC-V.

The instruction set architecture determines many implementation aspects, including the structure of the datapath and control logic. Signup and view all the answers

What is the primary difference in actions required after reading registers for different instruction classes in RISC-V?

The actions vary based on the instruction class, as they dictate how to manipulate data or control the flow of execution. Signup and view all the answers

In what ways does the RISC-V implementation illustrate the principle of 'Simplicity favors regularity'?

By maintaining a consistent set of operations for different instruction types, the design simplifies implementations and enhances predictability. Signup and view all the answers

What role does the ALU play in the execution of RISC-V instructions?

The ALU is used for address calculation in memory-reference instructions and for performing operations in arithmetic-logical instructions. Signup and view all the answers

How does a conditional branch instruction determine the next instruction address?

A conditional branch instruction compares values and can change the next instruction address accordingly; if no change is needed, the program counter (PC) increments by four. Signup and view all the answers

Why can't data lines simply be wired together in a RISC-V implementation?

Data lines cannot be simply wired together because the system requires a multiplexor to select one source from multiple inputs based on control signals. Signup and view all the answers

What is the function of a multiplexor in a RISC-V processor?

A multiplexor serves as a data selector that chooses among several inputs to steer one to its destination based on control lines derived from the instruction being executed. Signup and view all the answers

How do the actions required for memory-reference instructions differ from those for arithmetic-logical instructions?

Memory-reference instructions require access to memory for reading or writing data, while arithmetic-logical instructions involve writing results from the ALU or memory back into a register. Signup and view all the answers

Study Notes

4.1 Introduction

Computer performance depends on instruction count, clock cycle time, and clock cycles per instruction (CPI).
Instruction count is determined by the compiler and instruction set architecture.
Processor implementation determines clock cycle time and CPI.
This chapter details datapaths and control units for RISC-V instruction set implementations.
A simple overview of processor implementation principles is presented initially.
Pipelined RISC-V implementation is followed by more complex instruction sets like x86.

Basic RISC-V Implementation

Implementation includes a subset of core RISC-V instructions.
- Memory-reference instructions (lw, sw)
- Arithmetic-logical instructions (add, sub, and, or)
- Conditional branch instruction (beq)
This subset excludes shift, multiply, divide, and floating-point instructions.

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Description

This quiz covers the fundamentals of RISC-V processor implementation as described in Chapter 4.1. It focuses on key concepts like instruction count, clock cycle time, and the pipelined approach in processor design. The questions will also touch upon memory-reference, arithmetic-logical, and branch instructions within the core RISC-V set.