RE: [sv-ec] semantics of wildcard bins

Hi, Ray.

As a user reading this section for the first time, here are the
interpretations I would come to as answers to your questions:


> -----Original Message-----
> From: owner-sv-ec@server.eda.org [mailto:owner-sv-ec@server.eda.org]
On
> Behalf Of Ryan, Ray
> Sent: Wednesday, May 10, 2006 3:49 AM
> To: sv-ec@server.eda.org
> Subject: [sv-ec] semantics of wildcard bins
> 
> The last last paragraph of the section on wildcard bins (18.4.3)
states:
> 
> "A wildcard bin definition only considers 2-state values; sampled
values
> containing X or Z are excluded. Thus, the range of values covered by a
> wildcard bin is established by replacing every wildcard digit by 0 to
> compute the low bound and 1 to compute the high bound."
> 
> 
> 1) The statement about the range of values is not right or is
confusing.
> 
>    For example:
> 	wildcard bins bx = { 4'b?0?0 };
>    This does not cover the values in the range 0000 to 1010. It
doesn't
> cover 0001.
> 

[Shalom] Agree.


> 2) What does it mean that sampled values containing X or Z are
excluded.
> 
>    For example:
> 	wildcard bins bx = { 4'b?0?0 };
>    I would expect that if the sample value is:
>         0000	- increment the bin count
>         1000      - increment the bin count
>         0001      - don't increment
>         000X 	- don't increment
>         0010      - increment
>         00X0      - increment
>         00Z0      - increment
>     However, the text seems to indicate that the last two sample
values
> are excluded and
>     so don't increment the bin count.
> 

[Shalom] Yes, they are excluded. The text explicitly says that the ? is
a wildcard for 0 and 1 and that it works like ==?.


> 3) How many bins are created for
>     	wildcard bins bx[] = { 4'b?0?0, 4'b?000, 4'b00?0 }
>    I would expect that 3 bins are created.
> 

[Shalom] Agree.


> 4) How are wildcard ignore_bins handled?
>     For example:
> 	bins BA[2] = { 2'b00, 2'b1x };
>       bins BB[2] = { 2'b10, 2'b0x };
> 	wildcard bins BC = { 2'b0?, 2'b11 }
>       wildcard ignore_bins ivals = { 2'b00, 2'b?0, 2'b0? };
>       ignore_bins vals = { 2'b01, 2'b00, 2'b0x, 2'b0z };
> 
>     The ignore value 2'b00 will be removed from the first BA bin
causing
> the
>     bin to be ignored.
>     Will the ignore value 2'b?0 remove the 2'b10 value from BB ?

[Shalom] Yes.


>     Will the list of values in the last ignore_bins remove the
wildcard
>     value 2'b0 from BC ?

[Shalom] Yes.

Two more editorial quibbles:

The first example in this section is called g12_16 and increments "when
the sampled value is between 12 and 16". Actually the range is only
12-15.

Also, the first and third paragraphs in this section refer to "wildcard
bins", with both in Courier font. As a reader, I would be in doubt
whether or not this implies that 'wildcard' may only be used with 'bins'
and not with 'ignore_bins' and 'illegal_bins' (going back to the rule
that the BNF does not contain all the information and the text
supplements it). The simplest correction would be to de-Courierize
"bins' in those two places.

Shalom