I've came across some products that help you troubleshoot a computer that won't POST, with listening and capturing traffic on PCI bus during system startup.
They essentially know the normal procedure, and can tell you what is not going on as expected.
I know conventional PCI is a shared Bus, which means you can sniff the traffic that is not even addressed to you just by listening on the bus. You don't even have to introduce yourself to the controller since you are not going to send anything.
But these cards have a PCIe port too. Isn't PCIe a Peer-to-Peer connection? How are they capturing traffic that is targeted to other devices?
And is it possible to use an FPGA that doesn't have a dedicated PCIe endpoint integrated and isn't fast enough to operate on a 2GHz bus? Does the bus operate on a lower speed during POST or device initialization?
And after all, is it gonna work on newer hardware? Do they broadcast any useful messages during POST?