I am a beginner of computer architecture. I try to learn Y86 architecture. I got this reference for the Y86 architecture. I did not understand the picture Stage computation: Arith/log. ops. I have studied the book Computer Systems: A programmer's Perspective but the things are not clear to me

1. M1[PC]
2. M1[PC+1] and other lines

As per the book, M1[x] indicates accessing (either reading or writing) 1 byte at memory location x. That means M1[PC] means accessing(either reading or writing) 1 byte at memory location program counter. Is that make sense?

1. valP <- PC+2

But why it is PC+2 and not any other integer.

I also came to know from the book In the fetch stage, we do not require a constant word, and so valP is computed as PC + 2

But then again It is also possible fetches a 4byte constant word valC

So suppose, there is another line in the above example after rA:rB<-M1[PC+1] is valC<- M4[PC+2] then what will be the next line valP<-PC +______

Here I try to solve a small program following the link I refer here

Stage:  addq V, rB

Fetch:  icode : ifun ← M1[PC]

        rA : rB ← M1[PC+1]
        valC ← M8[PC+2]
        valP ← PC + 10

Decode: valB ← R[rB] 

Execute:    valE ← valB + valC

Memory:  

Write back: R[rB] ← valE 

PC update:  PC ← valP

Edited: I edit this question and try to understand how much knowledge I gain from the link.

Is my code alright?