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Questions and Answers
What is the base for the branch address calculation according to the instruction set architecture?
What is the base for the branch address calculation according to the instruction set architecture?
- The address of the previous instruction
- The address of the next instruction
- The address of the memory location
- The address of the branch instruction (correct)
What happens to the offset field in the branch instruction?
What happens to the offset field in the branch instruction?
- It is shifted left 1 bit (correct)
- It is shifted right 1 bit
- It is divided by 2
- It is multiplied by 2
What is the purpose of shifting the offset field?
What is the purpose of shifting the offset field?
- To reduce the number of bits required
- To make the calculation more complex
- To decrease the range of the offset field
- To increase the range of the offset field (correct)
What happens when the condition is true in a branch instruction?
What happens when the condition is true in a branch instruction?
What are the two operations performed by the branch datapath?
What are the two operations performed by the branch datapath?
What is the function of the immediate generation unit in the branch datapath?
What is the function of the immediate generation unit in the branch datapath?
What is the total number of steps involved in the execution of an R-type instruction?
What is the total number of steps involved in the execution of an R-type instruction?
What is the function of the main control unit during the execution of an R-type instruction?
What is the function of the main control unit during the execution of an R-type instruction?
How many registers are read from the register file during the execution of an R-type instruction?
How many registers are read from the register file during the execution of an R-type instruction?
What is the input to the control unit in the simple datapath?
What is the input to the control unit in the simple datapath?
What happens to the PC during the execution of an R-type instruction?
What happens to the PC during the execution of an R-type instruction?
How many clock cycles are required to execute an R-type instruction?
How many clock cycles are required to execute an R-type instruction?
What is the purpose of the opcode field in an instruction?
What is the purpose of the opcode field in an instruction?
What is the purpose of the rs1 field in an instruction?
What is the purpose of the rs1 field in an instruction?
What is the purpose of the rs2 field in an instruction?
What is the purpose of the rs2 field in an instruction?
What is the purpose of the rd field in an instruction?
What is the purpose of the rd field in an instruction?
What is the benefit of the first design principle from Chapter 2?
What is the benefit of the first design principle from Chapter 2?
How does RISC-V compare to MIPS in terms of instruction formats?
How does RISC-V compare to MIPS in terms of instruction formats?
Why is the single-cycle design not used in modern processors?
Why is the single-cycle design not used in modern processors?
What determines the clock cycle in a single-cycle design?
What determines the clock cycle in a single-cycle design?
What is the CPI (Cycles Per Instruction) for a single-cycle implementation?
What is the CPI (Cycles Per Instruction) for a single-cycle implementation?
Why was the single-cycle design used in early computers?
Why was the single-cycle design used in early computers?
What is the problem with using a single-cycle design with a fixed clock cycle?
What is the problem with using a single-cycle design with a fixed clock cycle?
Why wouldn't the single-cycle design work well with a floating-point unit or complex instructions?
Why wouldn't the single-cycle design work well with a floating-point unit or complex instructions?
What is the primary reason for specifying a clocking methodology in computer design?
What is the primary reason for specifying a clocking methodology in computer design?
What is the purpose of an edge-triggered clocking methodology?
What is the purpose of an edge-triggered clocking methodology?
What is the significance of a clock edge in an edge-triggered clocking methodology?
What is the significance of a clock edge in an edge-triggered clocking methodology?
Why do combinational logic elements need to have their inputs come from a set of state elements?
Why do combinational logic elements need to have their inputs come from a set of state elements?
What is the consequence of writing and reading a signal at the same time in a computer design?
What is the consequence of writing and reading a signal at the same time in a computer design?
What determines the output values of combinational logic elements?
What determines the output values of combinational logic elements?
Study Notes
Branch Instructions
- Branch instructions have two important details:
- The base for branch address calculation is the address of the branch instruction itself.
- The offset field is shifted left 1 bit, making it a half-word offset, and increasing the effective range by a factor of 2.
Branch Datapath
- The branch datapath must perform two operations:
- Compute the branch target address.
- Test the register contents to determine if the branch is taken or not.
- The datapath includes an immediate generation unit and an adder.
Instruction Execution
- A simple implementation scheme involves four steps:
- Instruction fetch and PC increment.
- Reading two registers from the register file.
- Executing the instruction.
- Writing the result to the register file.
- These steps occur in one clock cycle.
Instruction Format
- The opcode field is always in bits 6:0.
- The funct3 field (bits 14:12) and funct7 field (bits 31:25) serve as an extended opcode field.
- The first register operand is always in bits 19:15 (rs1) for R-type and branch instructions.
- The second register operand is always in bits 24:20 (rs2) for R-type and branch instructions.
Single-Cycle Implementation
- A single-cycle implementation has a fixed clock cycle, which is determined by the longest possible path in the processor.
- This path is likely a load instruction, which uses five functional units in series.
- Although the CPI is 1, the overall performance of a single-cycle implementation is likely to be poor due to the long clock cycle.
Clocking Methodology
- A clocking methodology defines when signals can be read and written.
- An edge-triggered clocking methodology means that values stored in a sequential logic element are updated only on a clock edge.
- This methodology ensures that hardware is predictable and that values are not read and written simultaneously.
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Description
This quiz covers the operation of registers and clocking methodology in computer architecture, including the timing of reads and writes.
