AMD Instinct MI250 microarchitecture (ROCm documentation)

First-party AMD architecture reference for CDNA2 / MI250. The source that actually names xGMI: states each 16-wide AMD Infinity Fabric link runs at 25 GT/sec for a peak transfer rate of 50 GB/sec per link (100 GB/sec bidirectional); that the two GCDs inside one MI250 OAM are joined by FOUR such links at 25 GT/sec giving 200 GB/sec peak transfer between the two GCDs, or 400 GB/sec bidirectional; and that in a multi-OAM node 'The GCD pairs 2 and 6 as well as GCDs 0 and 4 connect via two XGMI links'. Also gives the per-GCD controller topology (two fabric interfaces each driving four links, one configurable as PCIe), per-GCD HBM2e at 1.6 TB/sec, and that each GCD keeps its own PCIe x16 to the host.