Spec nugget: A x16 slot is essentially 16 independent serial links acting as one aggregated pipe.
is critical. At boot, the OS scans for devices on Bus 0. Every device responds with a 256-byte (or 4KB for PCIe) header that tells the OS: "I am a GPU, I need 256 MB of memory space at address X." pcie base specification
Have you hit a PCIe training issue or a bizarre link negotiation failure? The answer is almost always in Chapter 4 (Physical Layer) of the Base Specification. Spec nugget: A x16 slot is essentially 16
| Gen | Raw Bit Rate | Encoding | Effective per Lane (x1) | | :--- | :--- | :--- | :--- | | 3.0 | 8 GT/s | 128b/130b | ~985 MB/s | | 4.0 | 16 GT/s | 128b/130b | ~1.97 GB/s | | 5.0 | 32 GT/s | NRZ | ~3.94 GB/s | | 6.0 | 64 GT/s | | ~7.56 GB/s | Every device responds with a 256-byte (or 4KB
This is the highest layer, responsible for assembling and disassembling Transaction Layer Packets (TLPs).