How do I start a counter with a condition?

Question

I am trying to start a counter (0 to 9) with a condition, such as when the condition occurs the counter resets itself and starts counting till 10 and then starts from 0. But it doesn't work.

What I already have is:

always @(posedge clk ) begin
  if (enable  & sample)
    counter <= 4'b0;
  else 
    counter <= counter + 4'b1;

  if ( counter == 4'd9 )
    counter <= 4'b0;
  else 
    counter <= counter + 4'b1;
end 

Any help?

Answer 1

It looks like 'enable and sample' clear, other wise it increments. Also in your example the comparison to 9 overrides the previous value, this check will reset to 0 or increment. You need to put this condition inside the else.

always @(posedge clk ) begin
  if (enable & sample) begin
    counter <= 4'b0;
  end
  else begin
    if ( counter == 4'd9 ) begin
       counter <= 4'b0;
    end
    else begin
      counter <= counter + 4'b1;
    end
  end
end

I suspect that you actually do not want it to increment when enable is low? which means the initial synch reset logic needs to be updated.