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Probing PCI Express Bus A/D for interrupts

I am posting this for a customer - Art Hays  at the National Institute of Health -    Customer is Using QNX and has developed  his own driver to work with our E-Series Adpaters.  since these will be eventually EOL, Art is looking for assistance moving to the X-Series Adpater.


In order to evaluate x86 motherboards for our application we probe #INTA on the PCI bus.  We measure the time from the assertion of this signal by the A/D to the entrance of our interrupt routine.  Using this metric we have found only about 1 in 4 ATX motherboards are acceptable.  For example we just tested three Advantech ATX motherboards and only one qualified.  This is often due to the BIOS abusing Systems Management Mode but can be due to other factors such as PCI bridge chips.

In order for us to consider a PCI Express A/D we have to be able to still measure this metric.  However on the PCI Express there is no equivalent of the #INTA signal to probe because it is a serial bus.  I have looked into test equipment that decodes the PCI Express bus, and even JTAG stuff, but this is very expensive.

It would be very nice if there were a pin I could probe on the PCI Express A/D card itself that is asserted when the card is going to interrupt.  This is what I'd like you to ask- is there some way to probe a signal on the A/D that indicates it is interrupting?


Fred Milling

Technical Representative

National Instruments

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Hi Fred,


Sorry, I missunderstood some of what you were asking for the first time.


X Series PCIe devices were designed for the PCIe bus, so the timing and controll ASIC doesn't expose a signal that would indicate when it's interrupting.

If the goal were only to qualify motherboards, and not the DAQ devices, it might be possible to use a PCIe M series device. Since they were origionally designed as PCI devices, the PCIe versions have a bridge chip and there should be a trace between the STC2 and the bridge for the INTA line. That being said, there is no guarantee that we can even get to that signal. It could very possibly be burried on a middle layer of the pcb. But if the goal is only to qualify motherboards, it's not really our area to begin with. If the customer want's to pursue this it will take some effort to track down the routing on the board to even see if this is a viable option.


One thing to mention to the customer is that judging from this they should be able to use MSI with X Series on QNX.



Luke Brekke

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