Figure 12-5. Measuring Nominal Flight Time - Intel Pentium Pro Family Developer's Manual

The time difference between when a signal at the input pin of a receiving
agent (adjusted to meet the receiver manufacturer's conditions required for
AC specifications) crosses V
driving agent crosses V
manufacturer to specify that driver's AC timings.
An example of the simplest Flight Time measurement is shown in Figure 12-5. The receiver
specification assumes that the signal maintains an edge rate greater than or equal to 0.3V/ns at
the receiver chip pad in the overdrive region from V
that there are no signal quality violations after the input crosses V
measurement is similar for a simple Hi-to-Lo transition. Notice that timing is measured at the
driver and receiver pins while signal integrity is observed at the receiver chip pad. When signal
integrity at the pad violates the guidelines of this specification, and adjustments need to be made
to flight time, the adjusted flight time obtained at the chip pad can be assumed to have been ob-
tained at the package pin, usually with a small timing error penalty.
The 0.3V/ns edge rate will be addressed later in this document, since it is related to the condi-
tions used to specify a GTL+ receiver's minimum setup time. What is meant by edge rate is nei-
ther instantaneous, nor strictly average. Rather, it can best be described for a rising edge -- by
imagining an 0.3V/ns line crossing V
tending to V +200 mV, with the signal staying ahead (earlier in time) of that line at all times,
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until it reaches V +200 mV. Such a requirement would always yield signals with an average
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edge rate >0.3V/ns, but which could have instantaneous slopes that are lower or higher than
0.3V/ns, as long as they do not cause a crossing of the inclined line.

Figure 12-5. Measuring Nominal Flight Time

GTL+ INTERFACE SPECIFICATION
, and the time that the output pin of the
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were it driving the test load used by the
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to V
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at the same moment that the signal crosses it, and ex-
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+200 mV for a rising edge and
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at the pad. The Flight Time
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12-9