Yes, I've been referred to this article many times. But none of the reasons seems to apply. First, I am definitely using DMA transfers, not interrupts. Second, the signals that I am using as sources and gates are all internal to the chassis, namely, the timebase of the 6608 as the source and the RTSI3 line as the gate. Finally, I am nowhere close to the peak sustained throughput of the PCI bus (I'm trying to push 10MB/sec), at least I don't think so.
One interesting clue is that everything works quite robustly if I acquire with the 4472 cards alone and transfer the results via DMA, OR if I acquire buffered events with the 6608 card and transfer via DMA. But if I do both at the same time, the 6608 throws -10920 errors, even though the incremental throughput is tiny.
Has anyone else ever seen this kind of conflict on a PXI bus?