Datasheet

PCI Express Non-Transparent Bridge
Intel
®
Xeon
®
Processor C5500/C3500 Series
Datasheet, Volume 1 February 2010
166 Order Number: 323103-001
• BIOS enumerates the NTB in the local host address space. The mapping of the
remote host interface to the other system is done subsequently by higher level
platform software.
• This mechanism avoids the race condition and timing relationship between when
the two systems initialize. Each system initializes only its internal components and
does not have any dependency on the availability and timing of the second system.
3.12.2 Initialization Sequence with NTB Port Connected to Root Port
This usage model is discussed in Section 3.5.2 and Section 3.5.3. In this configuration,
the downstream root port on one system is connected to the secondary side of the NTB
on the second system. This configuration requires the crosslink configuration described
in Section 3.6.3, “Crosslink Configuration” , in order for the PCIE links in the system to
initialize and train correctly.
The root port must not be allowed to enumerate the NTB port in the remote host
memory space until the local host has completed the configuration of the NTB on the
Intel
®
Xeon
®
processor C5500/C3500 series. Otherwise, the remote host may detect
erroneous BAR and configuration registers. To ensure the correct order of the
initialization sequence in this configuration one flag bit is used, the remote host access
bit. Section 3.21.1.12, “NTBCNTL: NTB Control” Bit 1. At reset, bit is cleared. When the
remote host access bit is cleared, the remote host cannot access the NTB.
The BIOS executing on the local host first configures the local host interface of the NTB.
While this operation is underway, the remote host access bit is cleared. As a result even
if the remote host completes its initialization and tries to run a discovery cycle to
discover and enumerate the NTB, it is not allowed to access the NTB resources. So, the
remote host is prevented from enumerating the NTB until the local host has completed
the entire configuration of the bridge.
Once the NTB resources are fully configured, the BIOS sets the remote bus access bit.
Subsequently, if the remote host tries to discover and enumerate the NTB, it will
succeed. The BIOS also generates a hot-plug event to the remote host to indicate that
Endpoint device (bridge) is now functional. The root port can then service the hot plug
event and discover/enumerate the NTB.
Connecting the NTB port on one system to a root port on another system allows the
Intel
®
Xeon
®
processor C5500/C3500 series system to be connected to the root port of
any system, not necessarily a Intel
®
Xeon
®
processor C5500/C3500 series system.