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

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

Oops.  Make that VCS 2009.06 passed :)

On Tue, Oct 13, 2009 at 10:05 AM, Trevor Williams <pha...@gm...>wrote:

> 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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>