MadeEasy Test Series: CO & Architecture - Pipelining

Question

here why to take stall at the highlighted cell as its OPERAND FORWARDING and unless mentioned its EX-EX and its being followed without stall also, please clarify how to understand where Operand Forwarding is to be applied in such generalized cases., Thanks in advance :)

Comments

We have a stall in 5th clock of I3 because R3 from instruction I2 would be available after the memory access stage( since it is LOAD instruction). It is not EX-EX always. You need to look at the instruction and understand after what stage the operand is available.

Understand the datapath and you are good to go with pipelining questions.

Answer 1

Pay special attention whenever there are load or store word instruction, normally in ALU instructions(add,sub,mul etc.)

EX to EX forwarding is done but in case of load instruction the result will be available in 4th stage (MA) hence there will be also a stall in that case and MA to EX stage operand forwarding is used

Answer 2

because I2 is LOAD instruction , so R3  will be available in memory access stage therefore there is a stall.