RISC-V Instruction Set and Extensions

Questions and Answers

What does the Processor control depend on in the abstract view?

The type of instruction being executed (correct)

The size of the instruction set

The speed of the clock cycle

The complexity of the remaining units

Which signal is likely used to determine if a memory read operation is required?

RegWrite

PCSrc

Branch

MemRead (correct)

What is the likely output of the ALUOperation control signal during an 'add' instruction?

0000 (correct)

0010

0011

0001

Which of the following control signals would indicate a writing operation to memory?

MemWrite Signup and view all the answers

In the context of the Processor's operation, what does 'Branch=0' likely signify?

No jump occurs Signup and view all the answers

What role do multiplexers play in the processor implementation according to the given overview?

To select data from multiple sources going to a unit Signup and view all the answers

Which of the following statements is true about the data flow in the RISC-V architecture's implementation?

Instruction execution omits some aspects of data flow Signup and view all the answers

In the context of the provided machine code references, what does 'PC' stand for?

Program Counter Signup and view all the answers

What can be inferred from the statement 'Can’t just join wires together' regarding data handling in RISC-V?

Direct connections do not suffice for data routing Signup and view all the answers

Which instruction type is represented by 'I3-111010101' in the machine code?

Arithmetic operation Signup and view all the answers

What is the primary function of the M Extension in the RISC-V architecture?

It adds instructions for multiplying and dividing integers. Signup and view all the answers

Which RISC-V instruction is used for multiprocessor synchronization?

load-reserved (LR.W) Signup and view all the answers

What is the main purpose of the C Extension in the RISC-V instruction set?

To provide 16-bit equivalent instructions of popular operations. Signup and view all the answers

Which of the following instructions represent memory reference operations in RISC-V?

load word (lw) and store word (sw) Signup and view all the answers

How does the A Extension contribute to RISC-V architecture?

It supports atomic memory operations. Signup and view all the answers

What does the F Extension in RISC-V provide?

Operations specifically for floating-point numbers. Signup and view all the answers

Which instruction is used to compare values and branch in RISC-V?

branch if equal (beq) Signup and view all the answers

Which combination of extensions can be used to improve performance through reduced instruction length?

C Extension along with others Signup and view all the answers

What is the purpose of the 'auipc' instruction in the given context?

To calculate a long target address beyond the range of 'jal'. Signup and view all the answers

How is the relative address calculated in the program?

By subtracting PCpresent from the base address. Signup and view all the answers

Which two parts does the relative address get divided into?

Upper 20 bits and Lower 12 bits. Signup and view all the answers

Following the instruction steps, what is the final value of PCnew?

0x07FFF F018 Signup and view all the answers

What does the 'slt' instruction do in the RISC-V instruction set?

Compares two signed integers and outputs true if the first is less. Signup and view all the answers

What is the main distinction between 'slt' and 'sltu' instructions?

'slt' compares signed integers while 'sltu' compares unsigned integers. Signup and view all the answers

In the context provided, what does 'jalr' instruction accomplish?

It jumps to the address contained in a register, adding an immediate offset. Signup and view all the answers

What is the significance of using the base address in the structure of the program?

It provides a reference point for calculating addresses. Signup and view all the answers

What is the purpose of the auipc instruction in RISC-V?

To add an immediate value to the Program Counter (PC). Signup and view all the answers

Given a PC value of 0x00000008 and an immediate value of 0x10000, what will be the final value in register x11 after executing auipc x11, 0x10000?

0x10000 008 Signup and view all the answers

How is the relative address calculated in the example provided?

The base address is subtracted from the current PC value. Signup and view all the answers

What two parts does the relative address get divided into when using auipc?

Upper 20 bits and Lower 12 bits. Signup and view all the answers

What instruction follows auipc to compute the final address in register x10 in the provided example?

addi x10, x10, 0x018 Signup and view all the answers

If the base address of num3 is 0x1000 0020 and PCpresent is 0x0000 0008, what is the calculated relative address?

0x1000 0018 Signup and view all the answers

What is the immediate value used in the auipc instruction in the given example?

0x10000 Signup and view all the answers

What is the final value in register x10 after executing the complete sequence of instructions with the provided PC and base address?

0x1000 0020 Signup and view all the answers

Study Notes

RISC-V Processor Extensions

slti and sltiu Instructions: Compare two values with an immediate second operand.
M Extension: Introduces integer multiplication and division instructions for enhanced arithmetic operations.
A Extension: Supports atomic memory operations, facilitating multiprocessor synchronization using load-reserved (LR.W) and store-conditional (SC.W) instructions.
F and D Extensions: Provide a suite of operations specifically designed for floating-point numbers.
C Extension: Reduces popular RISC-V instructions to 16 bits, promoting memory efficiency and potentially boosting performance.

Instruction Set Overview

Core RISC-V Instructions: Include load word (lw), store word (sw), arithmetic-logical operations such as add and sub, and the branch if equal (beq) instruction.
PC-relative Addressing with auipc: Utilizes upper immediate values to enhance addressing capabilities, allowing relative references to memory locations based on the program counter (PC).

PC-relative Addressing Example

Instruction Use Case: To initialize a base address in a register using PC-relative addressing through:
- Calculating relative address: Base address – PCpresent
- Splitting relative address into upper and lower parts
- Utilizing the auipc and addi instructions to compute final address.

Addressing Beyond jal Instruction Range

Symbol Address Calculation: auipc helps calculate long target addresses beyond jal's range by:
- Determining relative address for control transfer.
- Dividing the relative address into upper and lower components.
- Executing auipc and jalr to change program control flow to the specified address.

Integer Comparison Instructions

slt and sltu: Compare two integer values, storing Boolean results in a register; slt for signed comparisons and sltu for unsigned comparisons.
Key outputs: Result of comparison is 1 if the first value is less, otherwise 0.

Processor Implementation Insights

Abstract Implementation View: Highlights data flow and control mechanisms in the processor architecture.
Multiplexers: Essential for directing data from multiple sources to processing units.
Control Signals: Critical for operation, dictating functionalities such as RegWrite, MemRead, MemWrite, and ALUOperation based on instruction type.

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Description

Explore the RISC-V instruction set, including various extensions such as M, A, F, D, and C. This quiz covers core instructions, comparison instructions, and memory operations, essential for understanding RISC-V architecture. Test your knowledge on how these extensions enhance performance and efficiency.