- Signals to toggle multiplexers across the datapath to perform different operations.
- Generated either using logic synthesis or ROM-based control.
ROM based Control
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We feed in certain bits of the instruction and the controller generates the appropriate control signals for each mux.
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We feed in
Inst[30], Inst[14:12], Inst[6:2] -
Inst[6:2]is part of the opcode field. -
Inst[14:12]- funct3 -
Inst[30]- one of the bits of funct7, useful in distinguishing between certain instructions of the same type. -
Simple and easy to implement.
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More space.
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Potentially slower.
Combinational Logic Gates
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Exactly what it sounds like.
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Instead of storing controls in ROM, generate them using instruction’s bits.
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Faster.
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More cumbersome.