| // Relatively simple LED driver to show presence of events, | |
| // e.g., network packets arriving. | |
| // LED on pulse lasts 2^(cw-1) cycles (0.27 seconds with default | |
| // parameter cw=26 and 125 MHz clock) for a single event. | |
| // With a "steady" stream of events, keeps going with that same | |
| // on time and off time, period 2^(cw) cycles. | |
| module activity( | |
| input clk, // timespec 8.0 ns | |
| input trigger, | |
| output led | |
| ); | |
| parameter cw=26; | |
| reg [cw-1:0] cnt=0; | |
| reg arm=0; | |
| wire start = trigger & ~cnt[cw-1]; | |
| always @(posedge clk) begin | |
| if (arm | (|cnt)) cnt <= cnt-1; | |
| if (start | ~(|cnt)) arm <= start; | |
| end | |
| assign led = cnt[cw-1]; | |
| endmodule | |