A. Explain why forwarding is done from MA-WB Buffer (shown in the Fig. 1) in cas

Question

A. Explain why forwarding is done from MA-WB Buffer (shown in the Fig. 1) in case of the instruction sequence in 2.b. (iii) whereas it is done from EX-MA Buffer in case of the following sequence: add $t0, $t0, St1; add $t0, $t0, $t2; add $t0, $t0, $t3 b. Using MIPS-like pseudo-code, present the logic for pipeline stalling while scheduling the second instruction in Q.2 b iii) Discuss how pipeline stalling is done. c. Explain with a state diagram the 2-bit memory scheme (4 state) for branch taking is useful in case of nested loops?

Explanation / Answer

3)
   a)
   Forwarding is done from MA-WB buffer in case of instruction sequence in 2.b because here we have to memory access like loading or storing stuff like .Therefore, the data will be available at memory stage due to which forwarding is done from MA-WB whereas in the other given case forwarding is done from EX-WB buffer because here arithmatic operations are taken place.Therefore,the resultant data will be available by the execution stage itself due to which forwarding is done from EX-WB stage.

THe main concept of forwarding is that to less the amount of stalls (delays ) .So wherever the accurate data is readily avaialble in the least time,forwarding is done from there (in layman language)
  

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