Forum: FPGA, VHDL & Verilog The difference between test bench and test on DE1 board

Author: mrquan (Guest)
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Hi all,
I am a student and I am working on a homework. Shortly, I will summary 
shortly the hw's requirement. It said some thing like that: At first, 
when counter goes from 0->7 then led 1 on; when the counter up to 8 then 
led 2 on, up to 9 then led 3 on. Next, when the counter comes to 10, it 
depends on a switch, if switch is on, led 4 on, if switch is off led 5 
on. And if led 4 on, it still to be on until counter comes to 14 then 
counter reset to 0 and comes back to first stage which means led 1 on. 
And similarly, if led 5 on, it still to be on until counter comes to 22 
then counter reset to 0 and comes back to first stage which means led 1. 
The requirement is described by a lots of word but shortly it will be 
like that after I design FSM for the problem. When I finish my code, 
test bench runs OK but when I run on Altera DE1 board, it did not run 
like my expectation. When the counter comes to 8,9,10 it runs nicely but 
next when led 4 or led 5 on, it immediately comes back to stage 1 (led 1 
on). Led 4 should be on 4 seconds or led 5 should be on 12 seconds 
before come back to stage 1. In test bench, it waiting but in the board 
nothing is waiting.
This is my code, hope you guys help me.

module controller(sw, clk, rst, led, y, Y); //This is top level module
 input sw, clk, rst;
 output [4:0] led;
 output reg [2:0]y=0,Y=0; //y: present state; Y: next state
 parameter [2:0] fer=0, ready=1, prepare=2, transfer=3, flush=4; //define finite state machine
 reg [4:0] count=0; //counter
 frequency_divider C1(clk, clk_out); //divider frequency for DE1 board, I use pin L1 (50Mhz)
 always@(count, sw,y)
                        fer: if (count==8)
                        ready: if (count==9)
                        prepare:  if ((count==10) & (sw==0)) 
                                          else if ((count==10) & (sw==1))
                        transfer: if (count==14)
                        flush: if ( count==22)
                        default: Y=2'bxx;


 always @(negedge rst, posedge clk_out)
    if (!rst) 
always @(negedge rst, posedge clk_out)
  if (!rst) 
    count = 0;
      else begin
        count = count + 1;
        if (y==transfer && count==15) //This to reset the counter
        else if (y==flush && count==23)
 assign led[0]=(y==fer); // led 0 on when the system in fermertation stage (stage 1) 
 assign led[1]=(y==ready);
 assign led[2]=(y==prepare);
 assign led[3]=(y==transfer);
 assign led[4]=(y==flush);
 module frequency_divider(clk_in, clk_out);
  input clk_in;
  output clk_out;
  reg [31:0] num=0;
  wire clk_out=num[24];
  always @(posedge clk_in) begin
    num <= num+ 1;

module test_controller; //test bench 
wire [4:0]led;
reg sw, clk, rst;
controller C1(sw, clk, rst, led);

initial begin

always begin
#1 clk=~clk;
always begin
#100 sw=~sw;


Author: Andreas Bergmann (Company: www.collion.de) (bergy)
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Hi mrquan,

first of all, welcome to the fantastic world of FPGA...
As you could see, simulating (unrouted RTL code) will show you the ideal 
behaviour before partitioning your logic in rather small alements with 
sublightspeed limited routing delays.

For this you will be never able to come in the situation you found on 
your hardware.
I will give you some idears and you might try to fix your Logic for 
yourself (at least try to do so for educational purposes)...

1) This might not be a real problem in this design, but it is bad coding 
Never use a clock which is generated by a simple clock devider.
Better to use a DCM or PLL element in your FPGA.
Best is to modify and use your clock devider as an Clock Enable

2) You are using an external input (sw) which is asynchronly to your 
logic. Other than in a simple RTL simulation, every littly cell of logic 
will se this input (switching) at a different time (in respect to the 
clock edge). So first of all synchronize your sw to the clock you are 
using, and use the resulting signal in your logic.

3) Last and most important here, you first always Block is completly 
asynchronous. So remember, every single bit of your state reg and count 
bits will arive at a different time at your logic in your real fpga. 
Synchronizing to clock will help you out...

Best Regards

: Edited by User


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