Simulation of I2C in Xilinx

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daisyzari

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we tried simulating an I2C verilog code in Xilinx. But then, it seems that the output waveform is not good. we really need help in understanding what's wrong with the simulation/output waveform. I attached the code and the waveform is shown below:



Thank you
 

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  • i2c_verilog.zip
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That's a lot of X's. Are you sure that all registers get a valid value at the start of the simulation?

I notice the rstn being asserted (going low) a very short time, but that looks a bit too optimisitc. How about asserting the reset during the first 100 ns, and see if that helps any.
 

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mrflibble,
I tried asserting the reset for the first 100ns and this is what we got:



Thank you so much for the help
 

daisyzari said:
I tried asserting the reset for the first 100ns ...
Click to expand...

Judging by the screenshot, that is not what you did though... In the screenshot the "rstn" is low for half a clock cycle just like before. Only now you do the assertion around t=100ns.

For a reset that is asserted from t=0ns to t=100ns, you need something like:

Code: 
initial begin
    rstn = 1'b0; // assert active low reset
    #100
    rstn = 1'b1; // de-assert active low reset
end

Note that for the sake of simplicity I assume you use the default timescale in ISIM (1 ns).

Also make sure that you use the proper reset polarity, in case you use other people's modules. A lot of xilinx stuff uses active high resets.
 
Last edited:

Umm.. but that's what we did or maybe we forgot to save it.. we'll check again.. thanks..

---------- Post added at 13:48 ---------- Previous post was at 13:42 ----------

This is what we did..

Code: 
	initial
	  begin
                     rstn = 1'b1; // negate reset
	      #100;
	      rstn = 1'b0; // assert reset
	      repeat(1) @(posedge clk);
	      rstn = 1'b1; // negate reset
                   end

is this correct?
 

is this correct?
Click to expand...

No. It does explains how you got the signal in the screenshot though... Anyway, I suggest you try my previous suggestion.
 

Did you get things working now?
 

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