$4.(25$ points$)$ The following codes run on the five$-$stage pipelined datapath. For each piece of code, answer the following questions.

a$)$ Without forwarding, insert the necessary number of 'nops' for the code to execute correctly.

b$)$ With the forwarding unit available $($only supports forwards MEM$->$ EX and WB$->$EX$),$ show how the code will execute. Mention the data that's forwarded between the stages. Use 'nops' only when necessary.

$```$

Code $1$:

sub t$1,$ t$2,$ t$3$

add t$1,$ t$4,$ t$5$

or t$4,$ t$2,$ t$6$

Code $2$:

and t$2,$ t$5,$ t$1$

sub t$3,$ t$2,$ t$0$

nor t$7,$ t$1,$ t$5$

Code $3$:

and t$2,$ t$5,$ t$1$

sub t$3,$ t$2,$ t$0$

nor t$7,$ t$2,$ t$1$

Code $4$:

lw t$1,22($t$0)$

and t$2,$ t$1,$ t$3$

Code $5$:

lw t$1,22($t$0)$

sub t$6,$ t$0,$ t$2$

xor t$3,$ t$1,$ t$5$