Re: [Iverilog-devel] The tranif1 test is not right?

[Trevor W. <pha...@gm...>]

VCS.2006.09 passed.

2009/10/13 Stephen Williams <st...@ic...>

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> I've been working on some fixes to the tranifX handling in Icarus
> Verilog. I fixed a couple bugs, but now the tranif1.v test in the
> ivtest suite no longer works. I've been puzzling over it, and I now
> think that the test itself is not valid. The meat of the program
> is here:
>
>   wire pin;
>   pullup   (weak1) (keep1);
>   pulldown (weak0) (keep0);
>   tranif1 (pin, keep1, pin);
>   tranif0 (pin, keep0, pin);
>
> This is trying to simulate a keeper circuit, the idea being if
> the "pin" is released to HiZ, the previous value will have left
> one of the keepers enabled.
>
> But I don't believe this should simulate properly. The tranifs
> are not drivers themselves, so if the external pin driver is
> released, "pin" will go to Z, which will close *both* gates and
> pin will stay HiZ.
>
> Can people who have access try the attached program on the Big 3?
>
> - --
> Steve Williams                "The woods are lovely, dark and deep.
> steve at icarus.com           But I have promises to keep,
> http://www.icarus.com         and lines to code before I sleep,
> http://www.picturel.com       And lines to code before I sleep."
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>
> module main;
>
>
>   // Model a pin with a weak keeper circuit. The way this works:
>   // If the pin value is 1, then attach a weak1 pullup, but
>   // if the pin value is 0, attach a weak0 pulldown.
>   wire pin;
>   pullup   (weak1) (keep1);
>   pulldown (weak0) (keep0);
>   tranif1 (pin, keep1, pin);
>   tranif0 (pin, keep0, pin);
>
>   // Logic to drive a value onto a pin.
>   reg  value, enable;
>   bufif1 (pin, value, enable);
>
>   initial begin
>      value = 0;
>      enable = 1;
>      #1 if (pin !== 0) begin
>         $display("FAILED -- value=%b, enable=%b, pin=%b", value, enable,
> pin);
>         $finish;
>      end
>
>      // pin should hold its value after the drive is removed.
>      enable = 0;
>      #1 if (pin !== 0) begin
>         $display("FAILED -- value=%b, enable=%b, pin=%b", value, enable,
> pin);
>         $finish;
>      end
>
>      value = 1;
>      enable = 1;
>      #1 if (pin !== 1) begin
>         $display("FAILED -- value=%b, enable=%b, pin=%b", value, enable,
> pin);
>         $finish;
>      end
>
>      // pin should hold its value after the drive is removed.
>      enable = 0;
>      #1 if (pin !== 1) begin
>         $display("FAILED -- value=%b, enable=%b, pin=%b", value, enable,
> pin);
>         $finish;
>      end
>
>      $display("PASSED");
>   end
>
> endmodule // main
>
>
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