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Lars · Guest

I stumbled upon the System Monitor feature in the Virtex-4 handbook
while looking for the DXN/DXP pins from Virtex-II for temperature
supervision. Perfect, just what we need! Both temperature and power
supply supervision, without the hazzle of external SMBus measuring
devices, voltage comparators and the like.

Only trouble is (gee wizz..) the feature is marked as "NOT supported"
in Xilinx Answer Record 20102.

Since that option seems to be out the window, are there still means to
supervise chip temperature? Or do we need to glue a sense diod atop
each package? Or maybe the System Monitor will be revived in later
stepping levels of silicon?

Anyone who knows?
/Lars

Symon · Guest

Hi Lars,
Well my V2PRO stuff works great and the FPGA is thrashing away while the
measurement is going on. As you say, I am very careful with my layout. And I
read the Maxim datasheet very carefully indeed!
Good luck, Syms.

Lars · Guest

It seems these pins are renamed TDP/TDN in Virtex-4. Good, so we don't
need to resort to glue...

I wonder if these pins are as succeptable to switching noise as DXP/DXN
in the Virtex/Virtex-E/Virtex-II? It seems the only way to aquire a
reliable reading is to stop clocking the device (Answer Record 11558).
In my experiance, Virtex readings where fairly stable, Virtex-E (at
least the devices I have used) gave a +15 degrees Celsius higher
reading than was the case, and Virtex-II again where fine in most
situations but could start to fluctuate wildly under certain
conditions. Maybe it was my board that was badly layed out... We used
the MAX1617A and the ADM1021.

I also wonder what became of System Monitor???

/Lars

Symon · Guest

Hi Lars,
I use a Maxim MAX6695 together with the DXN, DXP pins. Works lovely!
Cheers, Syms.

Austin Lesea · Guest

Lars,

What happened to the System Monitor?

Well, it is a long, and rough road, but we fixed it. Or at least, we
fixed everything that was wrong with it, or know how to, or have bits
and pieces of it working. I believe in the most recent stepping all
parts have 'working' (yet untested) system monitors.

What was left unfixed was gain error (the gain varies by more than we
would like it to, but we know how to fix that, too - we just did not).
The offset is automatically corrected, so that was never an issue.
Linearity was broken, and now it is fixed. The Vccaux voltage sensor
point also was measured at the wrong node (simple error, so we can do it
right next time).

What is left is the core voltage sensor (which works), the temp sensor
(which works), and the external voltage inputs, multiplexers, alarm
levels, scanners, etc. which all work (save for the variation in gain
that is beyond what we would have liked).

To re-introduce the feature this late in the game is just not possible,
so we will chalk this experience up to experimental silicon prototyping
that just happens to be in every part: and being on the "bleeding edge"
of the technology, and learning just how difficult mixed signal IC
design is (something we learn again and again, with each new technology
it seems).

If we did reintroduce it, we would have to specify it, and then test it,
and then deal with the yield loss for ones where it doesn't work. So,
we won't (do any of that above). But we did do the test program, and
screened enough to make sure that when we do it (again) we will be ready
for it.

We are supporting the system monitor for anti-tamper methods security
research, so it still has some (small) life in the real world.

Austin

Lars wrote:

Lars · Guest

OK Austin,
I sympathise. As a matter of fact, quite a few "bells and whistles"
where scrapped in my recent projects, some of them would have been
quite useful. Sometimes it is better to acknowledge the fact that it is
just not worth the effort... It would have been nice though. Better
luck next time! Me, I'll start looking for replacements for the
MAX1617, that part has caused enough greif.

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