2.10

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Questions and Answers

What does the instruction 'bne x10, x11, 2000' do?

It jumps to address 2000 if x10 is not equal to x11. (correct)

It jumps to address 2000 unconditionally.

It jumps to address 2000 if x10 equals x11.

It jumps to address 2000 if x10 is less than x11.

Which component is NOT part of the S format for conditional branch instructions like 'bne'?

rd (correct)

imm[12:6]

rs2

opcode

What is the opcode for conditional branches such as 'bne'?

1100001

0011101

1110000

1100111 (correct)

What is the immediate encoding limitation of the jal instruction?

It can only encode even addresses. Signup and view all the answers

What allows branch instructions to calculate larger program sizes?

Using a fixed register for the branch offset. Signup and view all the answers

In the U format for the jal instruction, what is the size of the address immediate?

20 bits Signup and view all the answers

What is the consequence of the immediate encoding limitation in branch instructions?

Programs cannot exceed 2^20 in size. Signup and view all the answers

What is the primary advantage of PC-relative addressing in RISC-V?

It likely targets instructions that are close to the current branch. Signup and view all the answers

What is the encoded distance that the 20-bit address field in jal instruction can represent?

±1 MiB Signup and view all the answers

Which instruction sequence is used for long jumps in RISC-V?

lui and jalr Signup and view all the answers

What limitation does RISC-V face regarding branch instruction reach?

They represent the number of halfwords rather than bytes. Signup and view all the answers

Which of the following ranges can conditional branches in RISC-V typically cover?

±210 words Signup and view all the answers

Why might procedure calls in RISC-V require a more extensive jumping mechanism?

The callee may be located far from the caller. Signup and view all the answers

What does the PC stand for in the context of branch addressing?

Program Counter Signup and view all the answers

What is the maximum number of halfwords a RISC-V branch instruction can encode?

±219 halfwords Signup and view all the answers

Which addressing mode utilizes a constant embedded within the instruction?

Immediate addressing Signup and view all the answers

What is the main characteristic of base or displacement addressing?

It adds a register value to a constant to find the operand's memory location. Signup and view all the answers

In PC-relative addressing, what is added to determine the branch address?

The program counter and a constant value Signup and view all the answers

What is the role of the 'lui' instruction in the RISC-V architecture?

To load the upper portion of a 32-bit constant into a register. Signup and view all the answers

If bit 11 of a constant is set in RISC-V immediate instructions, what must be done to handle this case appropriately?

Add 1 to the constant loaded with 'lui'. Signup and view all the answers

Which instruction format uses the funct7 field according to RISC-V encoding?

R-type instructions Signup and view all the answers

What is the maximum positive branch address that can be achieved using the RISC-V branch instruction format?

4094 Signup and view all the answers

Which of the following is NOT a type of addressing mode used in RISC-V instructions?

Stack-based addressing Signup and view all the answers

Which instruction format does RISC-V use for branch instructions?

SB-type with a 12-bit address immediate. Signup and view all the answers

What is the significance of decoding machine language in the context of RISC-V?

To interpret machine code for debugging or analysis Signup and view all the answers

What does the opcode field signify in RISC-V instruction encoding?

It specifies the operation to be performed. Signup and view all the answers

What does the term 'sign-extended' refer to in the context of RISC-V immediate values?

When immediate values are extended to maintain their sign during calculations. Signup and view all the answers

Why might the immediate field size restriction be problematic in RISC-V?

It restricts the range of load/store memory addresses. Signup and view all the answers

When converting the hexadecimal instruction 00578833 to binary, what is the resulting binary value?

0000 0000 0101 0111 1000 1000 0011 0011 Signup and view all the answers

How many bits are used to represent the opcode in the SB-type format of RISC-V branch instructions?

7 bits Signup and view all the answers

What happens if a register holds a 12-bit immediate value with bit 11 set when using 'addi'?

The immediate value is treated as negative in the computation. Signup and view all the answers

What is the primary purpose of synchronization in parallel computing?

To ensure that writing tasks complete before reading tasks start Signup and view all the answers

What occurs if synchronization is not implemented in a scenario where multiple threads write and read the same memory location?

There will be a data race, leading to inconsistent results Signup and view all the answers

What does mutual exclusion aim to achieve in the context of synchronization?

Ensure only one processor can access a critical section at a time Signup and view all the answers

What is typically required to implement synchronization mechanisms in a multiprocessor environment?

Hardware primitives that allow atomic read and modify operations Signup and view all the answers

In the analogy of the reporters, why is synchronization important for writing a consistent conclusion?

To prevent some reporters from writing before others have finished Signup and view all the answers

Which of the following best describes a data race?

Simultaneous write and read operations that can yield unpredictable results Signup and view all the answers

What role do lock and unlock operations play in synchronization?

They establish mutual exclusion for critical sections of code Signup and view all the answers

Why are synchronization instructions provided by hardware essential for efficient task coordination?

They ensure tasks can run on different processors without overlapping access Signup and view all the answers

Study Notes

Wide Immediates and Addresses

Large immediate values can be loaded using two instructions:
- lui: Loads the upper 20 bits of the desired value
- addi: Adds the lower 12 bits of the desired value
RISC-V uses PC-relative addressing for branches and jumps, making it efficient for short jumps.
For longer jumps, a two-instruction sequence is used:
- lui: Loads the upper 20 bits of the destination address into a temporary register
- jalr: Jumps to the address calculated by adding the lower 12 bits of the destination address to the temporary register

Addressing Modes

RISC-V supports several addressing modes to access operands:
- Immediate addressing: The operand is a constant within the instruction.
- Register addressing: The operand is a register.
- Base or displacement addressing: The operand is located at a memory location whose address is the sum of a register and a constant.
- PC-relative addressing: The branch address is calculated by adding a constant to the PC.

Decoding Machine Language

Risc-V machine instructions are encoded in a specific format with opcode, funct3, and other fields.
By analyzing the bit pattern of a machine instruction, we can determine the corresponding assembly language statement.

Parallelism and Synchronization

Parallel execution is easier when tasks are independent but often requires synchronization to ensure correct data sharing.
Data races occur when multiple threads access the same memory location, at least one being a write, and they occur consecutively.
Synchronization is essential in multiprocessor systems to prevent data races and ensure consistent results in multithreaded applications.
Lock and unlock operations are used to implement mutual exclusion, allowing only a single processor to access a critical section of code at a time.
Atomic operations are necessary for synchronization, allowing a read and a write to a memory location without interruption, ensuring consistency in concurrent operations.

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Description

Explore the various addressing modes and instruction sequences used in RISC-V for efficiently loading large immediate values and handling jumps. This quiz will test your understanding of immediate, register, base, and PC-relative addressing in RISC-V architecture.