Fetch$()$

Review pages $13$ to $15$ of lecture slide $$CSE$140\_$Lecture$-4\_$Processor$-1.$

Create a function named Fetch$()$ that reads one instruction from the input program text file

per cycle.

PC: As learned in the lecture, the CPU needs to fetch an instruction that is pointed by the PC

value and the PC value needs to be incremented by $4.$ Declare a global variable named $$pc$$

and initialize it as $0.$ Whenever you read one instruction from the input program text file,

increment the pc value by $4$ and read the ith instruction that is pointed by PC value, $4*$i$.$ For

example, if pc is $4,$ you will read $1$st instruction, which is the second instruction when we

count from $0.$

Next PC: After fetching an instruction, fetch step will increment the PC value by $4$ as can be

seen in the lecture slide. Declare one variable named $$next$\_$pc$$ and store $$pc$+4.$ Later, we

will need to choose the next cycle pc value among this next$\_$pc value and the branch target

address. We will discuss later but the branch target address will be updated by another

function that produces $$branch$\_$target$.$ So$,$ add a logic in this Fetch$()$ function that copies

one of the three possible pc values $($next$\_$pc and branch$\_$target$)$ to pc variable. This updated

pc value will be used for the next instruction fetch.