forwarding_unit.c

#include "hazard.h"

void forwarding(MIPS32Simulator * sim, Log log[MEM_SIZE])
{
   if(!sim->id_on || !sim->ex_on) /* no forwarding if pc met EOP */
      return;

   // no hazard 
   sim->fwd_ctrl.FwdA = 0x00;
   sim->fwd_ctrl.FwdB = 0x00;

   // EXE Forward - rs 
   if(sim->ex_mem_ctrl.RegWrite && 
      sim->ex_mem_reg.rd_num != 0 &&
      sim->ex_mem_reg.rd_num == sim->id_ex_reg.rs_num)
      sim->fwd_ctrl.FwdA = 0x02;

   // MEM Forward - rs
   if(sim->mem_wb_ctrl.RegWrite && sim->mem_wb_reg.rd_num != 0
   && !(sim->ex_mem_ctrl.RegWrite && sim->ex_mem_reg.rd_num != 0
   && (sim->ex_mem_reg.rd_num == sim->id_ex_reg.rs_num))
   && sim->mem_wb_reg.rd_num == sim->id_ex_reg.rs_num)
      sim->fwd_ctrl.FwdA = 0x01;

   // EXE Forward - rt
   if(sim->ex_mem_ctrl.RegWrite && 
      sim->ex_mem_reg.rd_num != 0 && 
      sim->ex_mem_reg.rd_num == sim->id_ex_reg.rt_num)
      sim->fwd_ctrl.FwdB = 0x02;

   // MEM Forward - rt
   if(sim->mem_wb_ctrl.RegWrite && sim->mem_wb_reg.rd_num != 0
   && !(sim->ex_mem_ctrl.RegWrite && sim->ex_mem_reg.rd_num != 0
   && (sim->ex_mem_reg.rd_num == sim->id_ex_reg.rt_num))
   && sim->mem_wb_reg.rd_num == sim->id_ex_reg.rt_num)
      sim->fwd_ctrl.FwdB = 0x01;
   
    // MUX - first source operand, hazard check
   if(sim->fwd_ctrl.FwdA == 0x02) /* EXE Forward */
   {
      sim->id_ex_reg.rs_val = sim->ex_mem_reg.ALU_result;
      print_forwarding(sim, log, "EXE");
   }
   if(sim->fwd_ctrl.FwdA == 0x01) /* MEM Forward */
   {
      sim->id_ex_reg.rs_val = (sim->mem_wb_ctrl.MemtoReg == ON) ? 
      sim->mem_wb_reg.load_data : sim->mem_wb_reg.ALU_result;
      print_forwarding(sim, log, "MEM");
   }

    // MUX - second source operand, hazard check
    if(sim->fwd_ctrl.FwdB == 0x02) /* EXE Forward */
    {
         sim->id_ex_reg.rt_val = sim->ex_mem_reg.ALU_result;
         print_forwarding(sim, log, "EXE");
    }
    if(sim->fwd_ctrl.FwdB == 0x01) /* MEM Forward */
    {
         sim->id_ex_reg.rt_val = (sim->mem_wb_ctrl.MemtoReg == ON) ?
         sim->mem_wb_reg.load_data : sim->mem_wb_reg.ALU_result;
         print_forwarding(sim, log, "MEM");
    }
    
}