Question

I am coding in Verilog a typical count-to-n-then-reset-to-0 counter. My module has the logic to increment and reset the counter.

My issue is that I don’t know where the counter itself should be defined.

I could pass the counter (as inout?) to the module. That’s ok, but the counter still has to be defined somewhere so it this doesn’t do me any good.

Nothing else except this module should touch the counter, so I’d like to have the counter created within this module, and not passed in or out.

Is this reasonably standard, and if so, will someone point to a reference please on how to instantiate the counter?

Here’s the code. As far as I can tell, it works. I haven’t implemented DIR == REVERSE yet.

Couple of interesting gotchas. The (now commented out) STEPPER=0 line was causing an error in a schematic; it thought that STEPPER was tied to ground as well as other logic.

Also, I use = instead of <= in some places involving counter – I was getting timing problems (I suppose.) The procedural assignment removed (hid?) the problem.

module cam(
    input [7:0] DIVISOR,
    input DIR,
    input SPINDLE,
    output reg STEPPER
    );

     parameter FORWARD = 1'b1;
     parameter REVERSE = !FORWARD;
     
     reg[7:0] counter = 0;
        
    always @(posedge SPINDLE) begin
    //  STEPPER = 0;
        if (DIR == FORWARD) begin
            counter = counter + 1;
            if (counter == DIVISOR) counter = 0;
            end
        else begin
        //  counter <= counter - 1;
        //  if (counter == (-1)) counter <= DIVISOR;
            end
    end
    
    always @(negedge SPINDLE) begin
        STEPPER = (counter == 0) ? 1 : 0;
    end

endmodule

Answer 1

It should just be defined as a register within the module. Here’s an example from some of my code.

module trigger(clk, rxReady, rxData, txBusy, txStart, txData);
input clk;
input [7:0] rxData;
input rxReady;
input txBusy;
output reg txStart;
output reg[7:0] txData;

integer count81; // Number of cells received over serial (start solving after 81)
reg[8:0] data[0:8][0:8];

integer state;

always @(posedge clk) begin
    case (state)
        read:
            if (rxReady) begin
                data[count81 % 9][count81 / 9] = rxData ? 1<<(rxData-1) : -1;
                if (count81 < 80) count81 <= count81 + 1;
                else begin
                    count81 <= 0;
                    state <= solving;
                end
            end
        // etc....                 
    endcase
end
endmodule