63
Mellanox Technologies Confidential
Rev 1.1
8
PCIe Express Pinouts Description for SNAPI
ConnectX-6 SNAPI cards offer improved performance to dual-socket servers by enabling
direct access from each CPU in a dual-socket server to the network through its dedicated
PCIe interface. The PCIe x16 interface is split into two PCIe x8 in a row, such that each of
the PCIe x8 lanes can be connected to a dedicated CPU in a dual-socket server. In such a
configuration, Socket Direct brings lower latency and lower CPU utilization as the direct
connection from each CPU to the network means the Interconnect can bypass a QPI (UPI)
and the other CPU, optimizing performance and improving latency. CPU utilization is
improved as each CPU handles only its own traffic and not traffic from the other CPU.
In order to allow this capability, a system with a special PCI Express x16 slot is required.
The below table provides the pin definitions of the required four special PCIe pins.
PCIe
pin#
Server Connection for 2x PCIe x8
mode
Server Connection for 1x PCIe x16
mode
Comments
B82
1Kohm pull up to 3.3VAUX
Either leave unconnected or pulled to
GND
Configure the card to work at
2x PCIe x8 or 1x PCIe x16
modes
A32
P signal of differential PCIe clock
(100MHz nominally) of the CPU
which connects to PCIe lanes 15-8 of
the PCIe connector
Not Connected
PCIe clock for ConnectX-6 PCIe
bus lanes [15:8]
A33
N signal of differential PCIe clock
(100MHz nominally) of the CPU
which connects to PCIe lanes 15-8 of
the PCIe connector
Not Connected
A15
PERST signal from the CPU which
connects to PCIe lanes 15-8 of the
PCIe connector
Not Connected
PERST (PCIe Reset) for
ConnectX-6 PCIe bus lanes
[15:8]
