Forwarding Control Signals

The following table shows the control values for the forwarding multiplexors that select either the register file values or one of the forwarded values.

Control signal Explanation
ForwardA = 00 First ALU operand comes from the register file.
ForwardA = 01 Forwarded from the previous ALU result
ForwardA = 10 Forwarded from data memory or the second previous ALU result
ForwardB = 00 Second ALU operand comes from the register file.
ForwardB = 01 Forwarded from the previous ALU result
ForwardB = 10 Forwarded from data memory or the second previous ALU result

The conditions for finding hazards and the control signals to resolve them are 
   if ( IF/ID.Rs == ID/EX.Rw ≠ 0 and ID/EX.RegWrite)
      ForwardA = 01        // EX hazard

   elseif ( IF/ID.Rs == EX/MEM.Rw ≠ 0 and EX/MEM.RegWrite )
      ForwardA = 10        // MEM hazard

   else  ForwardA = 00     // No hazard
 
   if ( IF/ID.Rt == ID/EX.Rw ≠ 0 and ID/EX.RegWrite )
      ForwardB = 01        // EX hazard

   elseif ( IF/ID.Rt == EX/MEM.Rw ≠ 0 and EX/MEM.RegWrite )
      ForwardB = 10        // MEM hazard

   else  ForwardB = 00     // No hazard




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