_start:         
        #save registers
        sw $t1, -4($sp)
        sw $t2, -8($sp)
        sw $v1, -12($sp)
        sw $v2, -16($sp)
        sub $sp, $sp, 16
        
        #set function parameters
        li $a1, 4  #set function parameters 
        
        #call function/subroutine        
        jal func1
        
        #restore saved registers
        lw $t1, -4($sp)
        lw $t2, -8($sp)
        lw $v1, -12($sp)
        lw $v2, -16($sp)
        addi $sp, $sp, 16
       
        #use return value $v1/v2
        ....
       
        
func1: ....

        #prepare returned value in $v1/$v2
        sw $v1, 10
        sw $v1, 100

        #return to the caller
        jr $ra