Mojo Clock Generation

Work In Progress

Here is my code so far. Looking for feedback as to how to make it better!

Known problems:

Generates warnings for ratios of <5:1 for the clock rate.

Phase shifting generates warnings.

// Module to generate a clock based off of the system clock and a desired frequency.
// Note: only frequencies that are factors of 2n of the system clock can be generated.
module clock_gen(
    input sys_clk, // System clock input
    output out_clk // Generated clock output
    );

    // A register to hold the output value
    reg out_signal;
    assign out_clk = out_signal; // Continuous assignment to the module output

    // User-settable parameters to control functionality of the clock
    parameter sys_freq = 0;
    parameter out_freq = 0;
    parameter phase    = 0; // 0->360: Undefined behavior out of this range.

    // Internal parameter (Do not set outside of the module!)
    // The frequency scale is the ratio of the input and output frequencies.
    // The scale is divided by two, because each count changes the edge, and
    // two edge changes make a single clock cycle.
    // In order to round to the nearest integer instead of truncating, the value is

    // bitshifted left, scaled, and bitshifted right. The second bitshift
    // right is the /2.

    parameter _internal_freq_scale = 
           ((((sys_freq/out_freq) << 1) + 2) >> 2);

// Create a register the proper width to hold a prescale counter

    // NOTE: The use of $clog2 requires that sys_freq and out_freq be
    // determined at compile time.

    reg[($clog2(_internal_freq_scale)-1):0] prescale;

    // Initial setup for the clock
    initial begin

        // To set the phase, start the frequency at some fraction of the
        // period.

        // However, as one full count 0->_internal_freq_scale is a half 
        //period, we have to

// do some extra work to get the phase right.
if (phase < 180) begin

            prescale = _internal_freq_scale - 
                        (_internal_freq_scale * phase)/360;

out_signal = 0;
end else begin

            prescale = _internal_freq_scale - 
                         (_internal_freq_scale * phase)/360;

            out_signal = 1;
        end
    end

    // Every edge of the system clock, increment the prescalar. When it hits
    // the proper value, flip the

    always @(posedge sys_clk) begin
        prescale = prescale + 1'b1;
        if (prescale == _internal_freq_scale) begin
            out_signal = ~out_signal;
            prescale = 0;
        end
    end

endmodule

Comments

Mojo Clock Generation

**Work In Progress**

Work In Progress