fpga4fun.com

Hi,

This little experimental project i did is to light the LED on whenever the button on the tact switch is press. however, the LED did not seems to response to tat.

So i thought maybe is the asynchronous problem as in the Debouncer. So i follow the similar coding as in the debouncer but cancelled out the PB_down and PB_up output since only 1 output is needed. But the results is the same.

I'm not sure whenever my code is correct either, just started to experimenting around with it for a few months.

Codes:
module testsw (clk, sw, LED1, LED2);
input clk;
input sw;
output LED1;
output LED2;

reg [22:0] cnt;
always@ (posedge clk) cnt <= cnt+1;

wire state;
debouncer swmod(.clk(clk), .PB(sw), .PB_state(state));

assign LED1 = ~cnt[22] & ~cnt[20];
assign LED2 = state;

endmodule

module debouncer(clk, PB, PB_state);
input clk;
input PB;

output PB_state;

reg PB_sync_0; always @(posedge clk) PB_sync_0 <= ~PB;
reg PB_sync_1; always @(posedge clk) PB_sync_1 <= PB_sync_0;

reg [15:0] PB_cnt;

reg PB_state;
wire PB_idle = (PB_state==PB_sync_1);
wire PB_cnt_max = &PB_cnt;

always @(posedge clk)
if(PB_idle)
PB_cnt <= 0;
else
begin
PB_cnt <= PB_cnt + 1;
if(PB_cnt_max) PB_state <= ~PB_state;
end

endmodule

Thanks in advance!

Regards,
LoneSync

Another question, is the "posedge" and "negedge" can only be use with "always@". I seems to get error if i use those 2 keywords with "if..else".

I'm thinking of assigning decimal to the posedge and negedge of PB_down and PB_up. Then based on the decimal, to light up the LED.

Thanks!

Regards,
LoneSync

Hi,

You don't need a debouncer for this purpose (but it doesn't hurt). So I think you need to take a step back... Did your earlier experiments work? Can you flash both LEDs?

If so, try some very simple code to synchronize button and connect it to LEDs: one LED should be on when pressed, the other when released:

Code: Select all

reg r1, r2;
always @(posedge clk) begin
  r1 <= sw;
  r2 <= r1;
end
assign LED1 = r2;
assign LED2 = ~r2;

If that doesn't work, then most likely you've set it up with the wrong pins (sorry I don't know how to fix that on Altera, I only know about Xilinx).


About @(posedge clk): Verilog can simulate many things that it can't implement on FPGA. In simulations, you can put @(...) before any statement in an always/initial block -- it means "wait until this change before executing the next instruction".

But for FPGAs, you have to write always @(...). The @ doesn't work anywhere else.

And you can never put @ inside the brackets of if (...), because it's not a condition.

Regards,

Nick

Currently my codes do work, when the switch is pressed, the LED is on.
The code r as below:

Code: Select all

module testsw (clk, sw, LED);
input clk;
input sw;
output LED;

wire swstate;
debouncer swmod(.clk(clk), .PB(sw), .PB_state(swstate));

reg LED;
always@ (posedge clk) if (swstate == 1) LED <= ~LED; else LED <= 0;

endmodule

module debouncer(clk, PB, PB_state);
input clk;
input PB;

output PB_state;
//output PB_down;
//output PB_up;

reg PB_sync_0;  always @(posedge clk) PB_sync_0 <= ~PB;
reg PB_sync_1;  always @(posedge clk) PB_sync_1 <= PB_sync_0;

reg [15:0] PB_cnt;

reg PB_state;
wire PB_idle = (PB_state==PB_sync_1);
wire PB_cnt_max = &PB_cnt;

always @(posedge clk)
if(PB_idle)
    PB_cnt <= 0;
else
begin
    PB_cnt <= PB_cnt + 1;
    if(PB_cnt_max) PB_state <= ~PB_state;
end

//wire PB_down = ~PB_state & ~PB_idle & PB_cnt_max;
//wire PB_up   =  PB_state & ~PB_idle & PB_cnt_max;

endmodule


will try ur code and see how it works out...

thanks anyway!!


I think my second post is a bit misleading.
Actually what i'm trying there is something like below:

Code: Select all

always@ (posedge clk)  if (posedge PB_down) LED <= ~LED; else LED <= 0;


but it seems like posedge / negedge cant be used with if..else in this arrangement. how come?

sorry for the misleading post.

"posedge clk" is an event, not a condition. You can only use it in "@(...)". And if you want your code to be synthesizable, you have to write "always @(posedge clk)" and no other edges (except maybe a reset).

Luckily, Jean's website example already has a signal that pulses for one clock cycle, every time the switch is pressed. It's "PB_down". So if you want to toggle the LED every time the switch is pressed, try:

Code: Select all

always @(posedge clk) if (PB_down) LED <= ~LED;

You don't want the "else LED <= 0" part! as this would make the LED go out immediately on the next clock cycle. You'd probably never see it lit.

Regards,

Nick

Thanks NickH for ur help...
now LED do lid on when buttons are pressed...
either ur filpflop method or Jean's method...

from buttons, now i proceed on...
so i'm now trying the pong game from Jean's web...
with all the tutorials, display on the VGA monitor is not a problem...

problem occurs when i want to use the button instead of the mouse to control the paddle...

Code: Select all

reg startpos = 319;
reg [8:0] position;

reg [15:0] cnt1;
wire cnt1max = & cnt1;

reg [15:0] cnt2;
wire cnt2max = & cnt2;

always@ (posedge clk) if (sw3_state) position = startpos;

always@ (posedge clk) begin
   if (sw1_state == 0)
      cnt1 <= 0;
   else if (sw2_state == 0)
      cnt2 <= 0;
   else
      if (sw1_state)
         cnt1 <= cnt1 + 1;
         if (cnt1max) position <= position + 1;
      if (sw2_state)
         cnt2 <= cnt2 + 1;
         if (cnt2max) position <= position - 1;
end

my intention is to let the paddle to start at the initial position...
i'm not so sure how to do that, so i add another switch to reset it to the position...

Regards,
LoneSync