[ibis-macro] Re: Samples per bit for AMI

  • From: "Todd Westerhoff" <twesterh@xxxxxxxxxx>
  • To: <ibis-macro@xxxxxxxxxxxxx>
  • Date: Fri, 30 Sep 2011 08:30:11 -0400 (EDT)

Ambrish,

They already do.  That's the point.

Todd.


--

Todd Westerhoff
VP, Software Products
SiSoft
6 Clock Tower Place, Suite 250
Maynard, MA 01754
(978) 461-0449 x24
twesterh@xxxxxxxxxx
www.sisoft.com


-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@freelists.
org] On Behalf Of Ambrish Varma
Sent: Thursday, September 29, 2011 2:02 PM
To: ibis-macro@xxxxxxxxxxxxx
Cc: wkatz@xxxxxxxxxx; scott@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Samples per bit for AMI


I agree with Kumar and Scott,
The moment we add something like 'Samples per Bit' in the spec and
legitimize models that only work at 1 particular number, I suspect model
makers will start producing models based on that.


Here is some suggested text that could go in the new BIRD:

On page 186 in Section 10 after the lines:

| 3.1.2.4 sample_interval
|
| This is the sampling interval of the impulse_matrix. Sample_interval
| is usually a fraction of the highest data rate (lowest bit_time) of
| the device.  Example:
|
|   Sample_interval = (lowest_bit_time/64)

Add the following text:

| The fraction (64 in the above example) is a number that is decided by
| the EDA tool based on the rise time of the analog drivers, simulation
| speed,  or other factors. The AMI model must be able to produce valid
| results at any sample_interval.


Please add/amend anything to make it more meaningful - or even suggest
something to add at some other place to make it absolutely clear to the
AMI model maker what to expect.

Thanks,
Ambrish.

Ambrish Varma   |  Member of Consulting Staff
P: 978.262.6431   www.cadence.com






-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@freelists.
org] On Behalf Of Walter Katz
Sent: Thursday, September 29, 2011 10:45 AM
To: scott@xxxxxxxxxxxxx; ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Samples per bit for AMI

Scott,

I do not disagree with your comments. I think you propose that IBIS 5.1
require that a model accept any samples per bit and that if the model
implementation does have such an internal limitation then the model should

do the Torque Conversion. SiSoft would accept this resolution.

Walter

-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Scott McMorrow
Sent: Thursday, September 29, 2011 10:28 AM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Samples per bit for AMI

Walter

I'm on the same page as Kumar.  The EDA tool can set the sample_interval
to
anything that it desires, to generate uniformly sampled data that is as
accurate as required.  A model that requires a fixed sample_interval is
contrary to the spec and is non-compliant.  There is nothing new here.  If
a
model is non-compliant, it needs to be sent back to the model maker and
get
fixed.  How is this different than any other non-compliant IBIS model?
Sometimes an IBIS model quality problem can be fixed by the user.
Sometimes
it cannot be fixed.  Any fix at the EDA
tool level using re-sampling is like putting lipstick on a pig.   In the
end, it's just a pig that does what it wants to do, not what it should do.

Scott

Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax

http://www.teraspeed.com

TeraspeedR is the registered service mark of Teraspeed Consulting Group
LLC


On 9/29/2011 10:19 AM, Walter Katz wrote:
> Kumar,
>
> On page 188 of IBIS 5.0:
>
> | 3.2.2 Arguments
> | | 3.2.2.1 wave
> |
> | A vector of a time domain waveform, sampled uniformly at an interval
> | specified by the ‘sample_interval’ specified during the init call.
> | The wave is both input and output. The EDA platform provides the
> | wave. The algorithmic model is expected to modify the waveform in
> | place by applying a filtering behavior, for example, an equalization
> | function, being modeled in the AMI_Getwave call.
>
> The waveform in and out of AMI_GetWave is " sampled uniformly at an
> interval specified by the ‘sample_interval’ specified during the init
> call"
>
> I think this is "uniformly sampled data". So your comment "Your
> proposal will prevent the eda tool to pass continuous waveform as
> accurately as possible." Is not logical and does not apply. What did
> you mean by "Your proposal will prevent the eda tool to pass
> continuous waveform as accurately as possible."
>
> Walter
>
>
> -----Original Message-----
> From: ibis-macro-bounce@xxxxxxxxxxxxx
> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of ckumar
> Sent: Thursday, September 29, 2011 10:09 AM
> To: Arpad_Muranyi@xxxxxxxxxx
> Cc: IBIS-ATM
> Subject: [ibis-macro] Re: Samples per bit for AMI
>
> there are various ways of "digitizing". You probably meant uniformally
> sampled data. Your proposal will prevent the eda tool to pass
> continuous waveform as accurately as possible.
>
> On Thu, 29 Sep 2011 13:54:40 +0000, "Muranyi, Arpad"
> <Arpad_Muranyi@xxxxxxxxxx>  wrote:
>> Kumar,
>>
>> Regarding: "It does not make any sense for the eda tool to be doing
>> the part of the models job.", I don't think this is what I am
suggesting.
>> In the computer world there is no such thing as continuous waveform.
>> Everything is sampled, digitized.  I don't see how we can go without
>> knowing how things are digitized.
>>
>> Thanks,
>>
>> Arpad
>>
> ======================================================================
> ===
>> -----Original Message-----
>> From: ibis-macro-bounce@xxxxxxxxxxxxx
>> [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of ckumar
>> Sent: Thursday, September 29, 2011 7:25 AM
>> To: twesterh@xxxxxxxxxx
>> Cc: IBIS-ATM
>> Subject: [ibis-macro] Re: Samples per bit for AMI
>>
>> I do not agree. Resampling may part of a adc(analog to digital
> conversion)
>> which may be more or less complex. The key part is that the model
>> should treat the incoming waveform as an analog/continuous waveform
>> and take it from there. It does not make any sense for the eda tool
>> to be doing the part of the models job.
>>
>> On Thu, 29 Sep 2011 08:10:46 -0400 (EDT), "Todd Westerhoff"
>> <twesterh@xxxxxxxxxx>  wrote:
>>> I'm with Arpad on this (which should surprise no one).
>>>
>>>
>>>
>>> This is a practical issue - there are models out there with
> undocumented
>>> requirements (e.g. samples per bit) and this is a standardized way
>>> of documenting those requirements so that users (and tools) can do
>> something
>>> about them.  The mere act of documenting a requirement should serve
>>> as
> a
>>> hint to the model developer that generalizing the model might be a
>>> good idea.
>>>
>>>
>>>
>>> What bothers me most are models that have an undocumented
>>> requirement,
>> run
>>> when that requirement isn't met, but produce incorrect results.
>>> What's the chance that the user notices a problem and does something
>>> about it?
>>> Virtually nil, in my experience.  The models that flatline or crash
>> (I've
>>> seen both) are actually doing the user a favor.  Better to have no
>> result
>>> than the wrong one.
>>>
>>>
>>>
>>> No one is suggesting that having a fixed (or limited)
>>> Samples_Per_Bit setting is a good idea.  We're not promoting bad
>>> programming practices; we're trying to ensure good simulation
>>> results.  If others are willing
>> to
>>> tell system designers to wait while suppliers rewrite algorithmic
>> models,
>>> great.  Seems silly to me, but maybe their users are more patient
>>> than mine.
>>>
>>>
>>>
>>> Todd.
>> ---------------------------------------------------------------------
>> IBIS Macro website  :  http://www.eda.org/pub/ibis/macromodel_wip/
>> IBIS Macro reflector:  //www.freelists.org/list/ibis-macro
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