The issue is not with the PXIe-8862 controller itself, but with the Schroff PXIe-1082 chassis we use and the backplane topology. Unlike NI PXIe-1082, which has a non-blocking PCIe switch and allows Peer-to-Peer (P2P) streaming between all peripheral slots, the Schroff chassis only supports P2P between certain slots.
In the Schroff PXIe-1082:
- Slots 5–8 are directly connected to the PCIe switch → P2P works reliably here.
- Slots 2–4 are connected through bridges via Slot 1 (System Controller) → P2P is limited or fails.
- Slot 1 is the controller slot and does not participate in P2P.
This explains why your custom device works when FPGA cards are in slots 5 and 6 (or 6 and 8), but not in slots 2 and 4.
On NI PXIe-1082, all slots connect directly to the switch, so P2P works in any slot combination.
Recommendation: For Schroff chassis, place P2P-enabled FPGA cards in slots 5–8. If full flexibility is required, use an NI chassis with a non-blocking backplane.
The PXIe-8821 is an older controller with PCIe Gen2 and less demanding backplane requirements. With Gen2, the bandwidth per lane is lower, and the P2P streams require less throughput → the bridge connections between slot 1 and slots 2–4 are sufficient. The PXIe-8881 and PXIe-8862 are modern controllers with PCIe Gen3/Gen4 and higher bandwidth.
