In this chapter
This chapter describes the PCI Express Gen3 controller on the SmartNICs, which handles the PCI Express interface to the host. The PCI Express configuration space as defined in Section 7 of PCIe3.0 is implemented within the PCI Express IP cores.
The PCIe block handles the data transfer between the host (server/motherboard) and the FPGA.
The performance of a SmartNIC will depend on the slot in which it is mounted: A SmartNIC mounted in a slot supporting PCIe Gen1 will have Gen1 functionality, a SmartNIC mounted in a slot supporting PCIe Gen2 will have Gen2 functionality, and a SmartNIC mounted in a slot supporting PCIe Gen3 will have Gen3 functionality.
DMA data transfers
The PCI Express controllers implement a number of DMA channels for data exchange between the host memory and the FPGA. All DMA data transfers are initiated by the FPGA.
The FPGA can initiate a DMA read from data in host memory or a DMA write of data to the host memory.
Number of lanes
The PCI Express controllers support ×1, ×4, ×8 and ×16 lane operation depending on the number of available lanes in the physical connector in the host. The number of active lanes is determined during the PCI Express enumeration process at boot time.
Maximum number of lanes
This table shows the maximum number of lanes supported by the PCI Express controller on a SmartNIC for different physical connectors.
|Routed Lines||Physical Connector|
PCI Express throughput
The achievable PCI Express throughput from the FPGA to the host memory and from the host memory to the FPGA depends on a number of different factors, such as:
- Number of active PCI Express lanes
- PCI Express maximum transaction layer packet (TLP) size (MAX_PAYLOAD_SIZE)
- Number of flow control credits
- Number of completion resources
Maximum PCI Express throughput
This table shows the maximum theoretical PCI Express throughput as a function of the number of PCI Express lanes and MAX_PAYLOAD_SIZE.
|MAX_PAYLOAD_SIZE [in bytes]||PCI Express Throughput [in Gbit/s]|
Required PCI Express bandwidth for NT100E3-1-PTP
This table shows the required PCI Express bandwidth as a function of frame size for frames with only a standard packet descriptor, for frames with also an extended packet descriptorand for frames with a default-length dynamic descriptor for an NT100E3-1-PTP SmartNIC running at line rate.
|Frame Size [in bytes]||PPS||Gbit/s to be Transferred over the PCIe Bus|
|Standard Descriptor||Extended Descriptor 9||Dynamic Descriptor 1 (default length)||Dynamic Descriptor 2 or 3 (default length)||Dynamic Descriptor 4 (default length)|