The document describes a numerical controlled oscillator (NCO) module with parameters for accumulator width, tick width, step width, and modulation width. It contains registers for the accumulator, ticks, and wrap signal. It accumulates the step value each clock cycle and resets or increments the ticks register depending on whether the accumulator overflows the modulation value.

1. module nco ( clk,resetb,step,modmask, ticks, fout);
parameter W_ACCUM = 24;
parameter W_TICK = 8;
parameter W_STEP = 24;
parameter W_MOD = 24;
input clk;
input resetb;
input [W_STEP-1:0] step;
input [W_MOD-1:0] mod;
input [W_TICK-1:0] mask;
output [W_TICK-1:0] ticks;
output fout;
reg [W_ACCUM-1:0] accum, accum_in;
reg [W_TICK-1:0] ticks;
reg wrap;
wire [W_ACCUM-1:0] sum = accum + step;
wire [W_ACCUM-1:0] rem = sum - mod;
wire over = (sum >= mod);
always @(posedge clk or negedge resetb)
if (~resetb) accum <= 0;
else accum <= accum_in;
always @(over or rem or sum) begin
if (over) begin
accum_in <= rem;
wrap <= 1;
end
else begin
accum_in <= sum;
wrap <= 0;
end
end
always @(posedge clk) begin
if (~resetb) ticks <= 0;
else begin
if (wrap)
ticks <= ticks + 1;
end
end
assign fout = |(ticks & mask);
endmodule
module ncotest;

2. reg clk;
reg resetb;
reg [23:0] step;
reg [23:0] mod;
reg [7:0] mask;
wire fout;
wire [7:0] ticks;
parameter W_ACCUM = 24; parameter W_TICK = 8;
parameter W_STEP = 24;
parameter W_MOD = 24;
nco nco1 (.clk(clk),.resetb(resetb),.step(step),.mod(mod),.mask(mask),.fout(fout),.ticks(ticks));
parameter PERIOD_NS = 36;
parameter DUMP_ON = 1;
real sys_freq;
initial begin
step = 0;
mod = 0;
mask = 8'b00000001;
sys_freq = 1000000000.0/(PERIOD_NS);
#300;
$display ("NCO Test. NCO Accumulator width is %0d bits, system clock period is %0d ns (%fMHz).",
W_ACCUM,
PERIOD_NS,
sys_freq
);
mod = 125 << 12;
step = 9 << 12;
nco_test (mod, step, 1000000);
mod = 3125 << 10;
step = 2304 << 10;
nco_test (mod, step, 1000000);
mask = 8'b10000000;
mod = 500 << 12;
step = (151 << 12) - 9566;
nco_test (mod, step, 1000000);
$display ("Done.");
$finish;
end
task nco_test;
input [23:0] mod_arg;
input [23:0] step_arg;

3. input interval;
integer interval;
integer start_time;
integer fout_edges;
begin
step = step_arg;
mod = mod_arg;
fout_edges = 0;
start_time = $time;
while ( ($time - start_time) < interval) begin
@(posedge fout);
fout_edges = fout_edges + 1;
end
$display ("For Mod=%0d(0x%h), Step=%0d(0x%h), Frequency of fout = %f Hz, Expected fout is %f Hz.",
mod, mod,
step, step,
((fout_edges*1.0)/($time - start_time))*1000000000.0,
((step*1.0)/(mod*1.0))*(sys_freq)/(mask*2.0)
);
end
endtask
initial begin
clk = 0;
forever begin
#(PERIOD_NS/2) clk = ~clk;
end
end
initial begin
resetb = 0;
#200 resetb = 1;
end
initial begin
if (DUMP_ON) begin
$dumpfile ("nco.vcd");
$dumpvars (0,ncotest);
end
end
endmodule