RE: 0003177: Real numbers with scale factors in digital delays

Hi Shalom,

You're right - the confusion is on my side; the scaling is of a time value in a delay with respect to the time value in a timescale unit specification, not with respect to a reference timescale. I was mixing up the specified delay with the "internal delay" value you used inyour explanation.

Marq

-----Original Message-----
From: Bresticker, Shalom [mailto:shalom.bresticker@intel.com]
Sent: Monday 9 August 2010 11:26
To: Marq Kole; verilog-AMS LRM Committee
Subject: RE: 0003177: Real numbers with scale factors in digital delays

Sorry,

I don't understand why you think I implied a default timescale.
It is true that most tools have a default and that it differs between tools, but I don't believe I related to that at all.

Please clarify.

Thanks,
Shalom

> -----Original Message-----
> From: owner-verilog-ams@eda.org [mailto:owner-verilog-ams@eda.org] On
> Behalf Of Marq Kole
> Sent: Monday, August 09, 2010 12:23 PM
> To: verilog-AMS LRM Committee
> Subject: RE: 0003177: Real numbers with scale factors in digital delays
>
> Hi Shalom,
>
> On your last remark - this would imply a default timescale directive -
> 1364-2005 (19.8, p.358) says that is simulator-specific and does not
> even offer a suggestion. I do agree that most users would apply a
> `timescale 1ns/1ps but that's not something to build a standard on.
>
> Simple test case:
>
> `timescale 1ns/1ps
>
> module test1 (output out, input in);
> assign #10ns out = in;
> endmodule // test1
>
> `timescale 10ns/1ps
>
> module test2 (output out, input in);
> assign #10ns out = in;
> endmodule // test2
>
> `timescale 1ns/1ps
>
> module tb1;
>
> reg in;
>
> initial
> in = 0;
>
> always
> #20 in = ~in;
>
> test1 mut1 (out1, in);
> test2 mut2 (out2, in);
>
> endmodule // tb1
>
> `timescale 10ns/1ps
>
> module tb2;
>
> reg in;
>
> initial
> in = 0;
>
> always
> #2 in = ~in;
>
> test1 mut1 (out1, in);
> test2 mut2 (out2, in);
>
> endmodule // tb2
>
> `timescale 1ns/1ps
>
> module test_timescale_time_value_tb;
>
> tb1 tut1;
> tb2 tut2;
>
> initial
> #1000 $finish;
>
> endmodule // test_timescale_time_value_tb
>
> Unfortunately, my Verilog compiler does not seem to allow time values
> in a delay - it "expects" another token than the 'ns' found here. As
> far as I can tell the above code is SV compliant ...
>
> Perhaps somebody wants to try this and tell me the results (or tell
> what I need to change in the test case without removing the time values
> from the delays).
>
> Marq
>
> -----Original Message-----
> From: Bresticker, Shalom [mailto:shalom.bresticker@intel.com]
> Sent: Monday 9 August 2010 10:40
> To: Marq Kole; verilog-AMS LRM Committee
> Subject: RE: 0003177: Real numbers with scale factors in digital delays
>
> Hi,
>
> > -----Original Message-----
> > From: owner-verilog-ams@eda.org [mailto:owner-verilog-ams@eda.org] On
> > Behalf Of Marq Kole
> > Sent: Monday, August 09, 2010 11:23 AM
> > To: verilog-AMS LRM Committee
> > Subject: RE: 0003177: Real numbers with scale factors in digital
> delays
> >
> > Good point - the problem would appear if the time unit uses 's' and
> the
> > sale factor would use 'f', 'p', 'n', 'u', or 'm'. Would require a
> > separator between scale factor and time unit.
>
> [SB] Hmm, wouldn't that give the correct result however you interpreted
> it?
> Note that SV requires that there be no separation between the delay
> value and the time unit.
>
> >
> > Just for my understanding - if I read your description then if I
> would
> > have
> >
> > `timescale 1ns/1ps
> > assign #10ns out = ~in;
> >
> > then the 10ns delay would be scaled by the 1ns time unit? I would
> > expect that I would get 10ns delay irrespective of the timescale unit
> > directive, only taking the timescale precision directive into
> account.
> > Otherwise I would get #10ns = 10n * 1ns = 10as ...
> >
> > If there is no scaling to the timescale unit then #10ns would be the
> > same as #10n s ...
>
> [SB] Good question. #10ns should give you a 10ns delay in any case. I
> think the idea was that if the time unit specified in the time literal
> is different than the time scale, then the delay value is scaled
> according to the ratio.
>
> Suppose you had
>
> `timescale 10ns/1ps
> assign #10ns out = ~in;
>
> Then the #10 delay value is scaled to the unit used in the time scale.
> This requires dividing by 10, so internally it becomes
>
> assign #1.0000 out = ~in;
>
> Regards,
> Shalom
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