Rules for Main

main is started by QTSPIM and returns control to QTSPIM. Because of this, it needs different rules.

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main's Prolog ( done at the start of main):

1. QTSPIM has set up the stack pointer register $sp.
2. Initialize the frame pointer: $fp = $sp - space_for_variables. The space for variables is four times the number of local variables.
   
3. Adjust the stack pointer: $sp = $fp.

main's Body:

4. main may use any register
5. main refers to local variables as disp($fp).
6. main may push and pop values on the stack using $sp.

Calling a Subroutine (as done by main):

7. Push any registers $t0-$t9 that contain values that must be saved.
8. Put argument values into $a0-$a3.
9. Call the subroutine using jal.

Regaining Control from a Subroutine (as done by main):

10. Pop any registers $t0-$t9 that main pushed in step 7.

main's Epilog (done at the end of main):

11. Load $s0 with 10.
12. Return to QTSPIM using syscall.