Controlling Stalls - the CRS
When the CRS is full must stall the pipeline ahead of CRS (the DRR, FETCH) and introduce bubbles in the pipe downstream
- Individual status lines will be used by the CRS back to the DRR to indicate which ISSUED instructions were accepted.
- The CRS will always dispatch 4 instructions/clock to execution units. If there is not a valid instruction to dispatch, then will dispatch a NOP. The NOPs will act as bubbles in the pipeline downstream of the CRS.
If an issued instruction is a NOP, then accept it BUT do not place it in a shelving buffer (NOPS do not take up resources!)