Reuse a Speed Grade -8 Stratix image in Speed Grade -6 ...?

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Hello Group.

Quite simple question... but I cannot seem to be able to find the
answer:

Given a Code Image initially targeted for a Stratix EP1S40F780C8 - i.e.
Speed Grade "-8" - would it then be without troubles to load and run
that Image on the corresponding "-6" device...?

The need for the question arises in the crossfire of device
availability and the wish of having only one Coding Image to update.

Thanks in advance & best regards,

  Jesper.


Re: Reuse a Speed Grade -8 Stratix image in Speed Grade -6 ...?

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If the design is fully synchronous then there should be no problems, bearing
in mind Altera's oddball numbering system where the higher the part suffix
the slower the part.

However if you have any dodgy asynchronous behaviour included in the design
which relies on things having certain prop. delays to work then definatley
not - but you didn't design/verify it like that - did you?

You also need to check out the significance of the 'I' and 'C' (industrial
and commercial) speedgrades and verify that your substitute part is indeed
faster over your desired operational temp. range.

Slurp



Re: Reuse a Speed Grade -8 Stratix image in Speed Grade -6 ...?

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Hi Jesper,
As far as I know there should not be any issue with that approatch
since the device has the same ID:code. AFAIK the only diffrence between
-6 and -8 is that Altera gets more parts off the waffer that meets the
-8 spec than -6 spec (waffer sort).
I just tried programming a CycloneII -7 with a -8 speced file without
problem.
Hope this helps
Fredrik


Re: Reuse a Speed Grade -8 Stratix image in Speed Grade -6 ...?
Jasper -


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If the -6 parts don't work, your -8 parts might not work reliably,
either.  Perhaps this isn't obvious, so let me explain.

As a rule, FPGA vendors use the very same die design for every speed
grade.  They make a bunch of wafers, test each part for functionality
and speed, then separate the working parts according to speed grade.  

But suppose the vendor has the bad luck to have a lot of slow-speed
part orders sitting around, but happens to have a surplus of
fast-speed parts on hand.  It wouldn't be practical to keep cranking
out wafers until they get some slower parts, because there's no
telling when they'll get them.  Murphy says that when you want slow,
you get fast.  

So what digital parts vendors do, almost without exception, is spec
their parts so that the faster speed grade parts can be substituted
for lower-speed parts in a pinch.  If you're ordering slow-grade
parts, there's absolutely no guarantee that the vendor hasn't marked
some fast-grade parts with the slower speed grade number and sent them
to you.  

Of course, the vendor has to guarantee that all faster parts meet the
specs for the slower parts.  This is done through careful specmanship.
For example, take a look at the Stratix AC specs for I/O
clock-to-output times: all speed grades have the same minimum spec (at
least from what I can tell from a brief perusal of the data sheet).
This is important, because if you calculated external hold time
margins based on a long minimum clock-to-Q, then substituted a part
with a faster clock-to-Q, you could get into trouble.  But as long as
the vendor has been smart about choosing specs, remarking a faster
part as a slower one is all perfectly above-board and legal.

And has been pointed out by others, all of this is moot if you're not
using solid synchronous design techniques.

Bob Perlman
Cambrian Design Works
http://www.cambriandesign.com

Re: Reuse a Speed Grade -8 Stratix image in Speed Grade -6 ...?
Faster speed grade parts will work in almost all scenarios. While min
timing analysis should be conducted to ensure there are no timing
problems, likelihood is extremely high that faster speed grade parts
will work. To do min timing analysis from the UI use
Processing->Start->Start Timing Analyzer (Fast Timing Model).

Hope this helps
- Subroto Datta
Altera Corp.




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