Call

state_call1: begin
    // transfer arg2 to address
    arg2_drive = 1'b1;
    address_write = 1'b1;
    next_state = state_call2;
end

state_call2: begin
    // transfer IAR+4 to mem[arg2]
    iar_drive = 1'b1;
    memory_write = 1'b1;
    next_state = state_call3;
end

state_call3: begin
    // transfer arg1 to IAR
    arg1_drive = 1'b1;
    iar_write = 1'b1;
    next_state = state_fetch1;
end