[ibis-quality] 3.1.2 investigation

From: "Mike LaBonte (milabont)" <milabont@xxxxxxxxx>
To: <ibis-quality@xxxxxxxxxxxxx>
Date: Fri, 28 Oct 2005 12:14:00 -0400

The question came up as to whether IQ check 3.1.2 duplicates the
existing ibischk4 check for [Package]. The IQ check is:
 
  3.1.2 {LEVEL0} [Package] Parasitics must be reasonable

  Reasonable values are: L < 10nH, C < 20pF, R < 1 ohm
  Min must be less than typ and typ less than max.

I found out what the limits are for ibischk4:
 
IBISCHK4 V4.1.1
 
Checking bcm1250_ab.ibs for IBIS 4.1 Compatibility...
 
WARNING - CMPT 'BCM1250_Rev_AB': Rpkg TYP value 1100 Ohms not within
expected range (0 Ohms, 50 Ohms)
WARNING - CMPT 'BCM1250_Rev_AB': Lpkg TYP value 10100nH not within
expected range (0nH, 1000nH)
WARNING - CMPT 'BCM1250_Rev_AB': Cpkg TYP value 20100pF not within
expected range (0pF, 1000pF)


As I recall this was tested and discussed before and we decided the
ibischk limits are too high. Ibischk also does not check for typ/min/max
swizzles. Not sure why.

An idea for improving the [Package] swizzle check is to check R for
typ/min/max order, and to check the sqrt(LC) delay too. In other words,
don't check C and L independently, but check the resulting delay.

The IBIS spec is not clear (to me) on whether the min [Package] is
supposed to be the slowest or the fastest. A BIRD may be needed to fix
this, and it was suggested at the IBIS Open Forum today that BIRDs
should go in soon to make IBIS 4.2.

It occurs to me after writing the last paragraph that another way to
explain the difference between a WARNING and a CAUTION is that the
WARNING pertains to something explicitly stated in the IBIS spec, and a
CAUTION does not. Not sure if this is completely true.

I'd like to put this on the agenda for the Nov 1 call.

Mike
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[ibis-quality] 3.1.2 investigation

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