Synchronizing multiplier with adder to form mac
Add a counter and assign prev_sum to result on every eighth clock. 

always @(posedge clk) begin
  if (reset) begin
    prev_sum &lt;= 16'h00;
    counter &lt;= 3'b000;
  end
  else begin
    if (counter == 3'b111) begin
      prev_sum &lt;= result;
      counter &lt;= 3'b000;
    end
    else begin
      counter &lt;= counter + 1'b1;
    end
  end
end