42 Questions
What is the purpose of generating control signals in a pipelined processor?
To decode instructions and produce control values
Why do some control signals need to be propagated through the pipeline?
Because they are needed in a later stage and clock cycle
How are control signals propagated through the pipeline?
Through the pipeline registers, along with the other data
How are control signals categorized?
By the pipeline stage that uses them
What control signals are needed in the MEM stage?
MemRead and MemWrite
What is the purpose of the PCSrc control signal?
To select the next instruction address
What is the function of the RegDst control signal?
To select the register to write to
What is the purpose of the ALUSrc control signal?
To select the ALU operation
What is the purpose of the MemRead control signal?
To read data from memory
What is the purpose of the MemToReg control signal?
To select the data to write to a register
What is the purpose of propagating values forward in a pipelined datapath?
To ensure that any data values required in later stages are available
What is the function of the PCSrc signal in the pipelined datapath?
To determine the next program counter value
What is the purpose of the RegWrite signal in the pipelined datapath?
To write data to the register file
What is the function of the MemRead signal in the pipelined datapath?
To read data from memory
What is the purpose of the ALU in the pipelined datapath?
To perform arithmetic and logical operations
What is the purpose of the Shift Left 2 unit in the pipelined datapath?
To shift the offset value left by 2
What is the purpose of the Sign Extend unit in the pipelined datapath?
To sign-extend the immediate value
What is the purpose of the Instr [15-0] register in the pipelined datapath?
To store the instruction opcode
What is the purpose of the Instr [20-16] and Instr [15-11] registers in the pipelined datapath?
To store the register indices
What is the purpose of the RegDst signal in the pipelined datapath?
To select the destination register
What is the main difference between the original single-cycle datapath and the modified datapath?
The datapath components have been rearranged to accommodate pipeline registers.
What determines the actual memory operation in the modified datapath?
The MemRead and MemWrite control signals.
Why are the pipeline registers named after the stages they connect?
To simplify the diagrams.
What is the reason for not having a register after the WB stage?
The register is not needed after the WB stage.
What is the purpose of adding intermediate registers to the pipelined datapath?
To break the pipeline into stages.
What is the main advantage of having separate memories for instructions and data?
It allows for more efficient access to instructions and data.
What is the instruction in the MEM stage?
lw $8, 4($29)
What is the operation performed in the EX stage?
Addition
What is the purpose of the PCSrc signal?
To generate the next PC value
What is the register being written in the WB stage?
$8
What is the operation performed in the ID stage?
Instruction Decode
What is the purpose of the RegWrite signal?
To control the write back of results
What is the address used in the lw instruction?
($29)
What is the purpose of the MemWrite signal?
To control memory accesses
What is the main benefit of pipelining?
It increases the amount of work done per unit time.
What is a characteristic of the MIPS instruction set that makes it easy to pipeline?
All instructions are 32-bits long.
Why is pipelining harder for older, more complex instruction sets?
They have variable-length instructions.
What is a consequence of having memory-to-memory instructions in an instruction set?
The pipeline needs additional stages to compute effective addresses and read memory.
What is the relationship between the execution time of a single instruction and pipelining?
Pipelining does not improve the execution time of a single instruction.
What is a characteristic of the MIPS instruction set that simplifies the pipeline?
It is a register-to-register architecture.
What is the result of pipelining on the execution time of a sequence of instructions?
It decreases the execution time.
Why does pipelining improve throughput?
It allows multiple instructions to be executed together in each clock cycle.
Study Notes
Pipelining and Control Signals
- Control signals are generated after an instruction is fetched and decoded, producing appropriate control values.
- Control signals are categorized by the pipeline stage that uses them:
- EX stage: ALUSrc, ALUOp, RegDst
- MEM stage: MemRead, MemWrite, PCSrc
- WB stage: RegWrite, MemToReg
Pipeline Registers and Datapath
- Control signals are propagated through pipeline registers along with other data.
- The datapath components have been moved around in preparation for adding pipeline registers.
- Separate memories are used for instructions and data.
- There are two adders for PC-based computations and one ALU.
- The control signals are the same as in the single-cycle processor.
Propagating Values Forward
- Data values required in later stages must be propagated through the pipeline registers.
- Almost all components are the same as in the original single-cycle datapath, with some cosmetic changes.
Pipeline Registers
- Intermediate registers are added between each stage of the pipeline.
- The registers are named for the stages they connect: IF/ID, ID/EX, EX/MEM, and MEM/WB.
The Pipelining Paradox
- Pipelining does not improve the execution time of a single instruction, but increases throughput.
- Each instruction takes longer to execute than in a single-cycle datapath, but the result is improved execution time for a sequence of instructions.
Instruction Set Architectures and Pipelining
- The MIPS instruction set was designed for easy pipelining.
- All instructions are 32-bits long, which simplifies the instruction fetch stage.
- Fields are in the same position in different instruction formats, making it easy for the ID stage.
- MIPS is a register-to-register architecture, which keeps the pipeline simpler.
- Pipelining is harder for older, more complex instruction sets.
This quiz covers the generation and propagation of control signals in a pipelined processor, including how they are generated and when they are needed in the pipeline.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
