Which control signal in Figure 4.24 is the most critical to generate quickly and how much time does the control unit have to generate it if it wants to avoid being on the critical path?

In this exercise we examine how the clock cycle time of the processor affects the design of the control unit, and vice versa. Problems in this exercise assume that the logic blocks used to implement the datapath have the following latencies:

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PC Instruction [25-0] Add Read address Instruction [31-0] Instruction memory 26 Shift left 2/ Instruction [31-26] Instruction [25-21] Instruction [20-16] Instruction [15-11] Instruction [15-0] Jump address [31-0] PC +4 [31-28] Control MUX 28 RegDst Jump Branch MemRead MemtoReg ALUOD MemWrite ALUSIC RegWrite Read register 1 Read register 2 16 Read data 1 Write Read register data 2 Write data Registers Sign- extend Instruction [5-0] 32 Shift left 2, XERO Add ALU result Zero ALU ALU result ALU control/ Address (o Ex- 0 1 Read data Write Data data memory MUX OXER