LaRC 158/MAPLD 2004 Robert F. Hodson, NASA LaRC Kevin Somervill, NASA LaRC Mark Jones, NASA LaRC Guy Gibson, Northrop Grumman Actel Compact PCI Signal

LaRC158/MAPLD 2004

Robert F. Hodson, NASA LaRCKevin Somervill, NASA LaRC

Mark Jones, NASA LaRCGuy Gibson, Northrop Grumman

Actel Compact PCI Signal Integrityfor RTSXS & SXA devices

LaRCHodson - 2 158/MAPLD 2004

Initial simulations

These initial simulation performed by Northrop Grumman raised questions and concerns that prompted this study.


Actel Datasheet info (continued)


Datasheet info (continued)

What about 3.3V operation?






PCI Specifications

• PCI and Compact PCI designed for commercial systems

• Puts the onus on manufacturers to tolerate a broad range of operating conditions

• The following should be use to evaluate long term device reliability

Appears to contradict the maximum ratings of

Actel’s devices


cPCI Driver Simulations

• The following slides show HyperLynx simulations performed at NASA LaRC to simulate an Actel device (in slot 3) driving another Actel device (in slot 7).

• 3.3V PCI I/O is used• 20 degrees C• The simulation is done for both the RTSXS devices

and SXA commercial devices• Simulations with Spartan and Vertex II IBIS models

are also shown for comparison.


HyperLynx Schematic


RTSXS Model – slot 3 driving slot 7

Note: datasheet maximums exceeded


Non-monotonic signal in transition region


Sxacom Model – slot 3 driving slot 7

Note: datasheet maximums exceeded


Spartan model – slot 3 driving slot 7

Note: similar undershoot, cleaner signal.


Vertex II – slot 3 driving slot 7


Lab Test Setup

• Actel source board (Actel 3.3V PCI I/O) in slot 3– A54SX32A device with Actel PCI core

• Actel destination board (Actel 3.3V PCI I/O) in slot 7– A54SX32A device with Actel PCI core

• Commercial PCI bus• Commercial processor board in slot 1• 33 MHz operation


Data line showing under/overshhoot


Non-Monotonic signal at receiver


Actel Responses 8/18/04

• Actel has performed experiments on the PCI clamp diodes of the RTSXS device.

– In the 3.3V PCI configuration, the Power Clamp diode effectively clamps any incoming voltage (up to 7.1V) to about 4.6V. This is within Actel’s maximum rating (5.75V).

– The Ground Clamp diode clamps any incoming undershoot (up to -3.5V) to –1.2V. This clamped voltage is outside the maximum rating specified by Actel (-0.5V)

• PCI Reliability (260+ hour stress test)– Actel is performing a reliability experiment on the RTSXS IO buffer in the

PCI configuration to test the effect of input voltage excursions outside the normal operating rage. In this experiment the RTSXS device with the IO buffers configured as 3.3V PCI inputs are stressed continuously to a switching signal that conforms to PCI requirements (VIH=7.1V and VIL=-3.5V with a pulse width of 11ns each). Preliminary pre and post stress measurements were taken for Leakage and VIH/VIL. The maximum IIL/IIH delta was of the order of a few nanoamps and maximum VIH/VIL delta of about 50mV.

• Based on the reliability results so far, we don’t believe there is any issue with input voltages switching beyond the rails, as long as it is within PCI specifications. Upon completion of the reliability testing the datasheet will be updated.

– The experiment was done on a MEC device. The same experiment is being repeated on a UMC device (RTSX-SU).


Summary

• There appear to be inconsistencies between the Actel data sheets and the PCI specification

• Overshoot and undershoot in the simulations and the lab appear to exceed maximum rating for Actel 3.3V PCI I/O

• Non-monotonic behavior observed in simulations and the lab. Did not affect operation in this single test case, effect on other vendor devices unknown.

• Initial Actel over/undershoot testing has not uncovered reliability issues with PCI

• Actel plans to continue testing and update data sheets

Documents

LaRC 158/MAPLD 2004 Robert F. Hodson, NASA LaRC Kevin Somervill, NASA LaRC Mark Jones, NASA LaRC Guy Gibson, Northrop Grumman Actel Compact PCI Signal