58 SBC329 3U VPX Single Board Computer
Publication No. SBC329-HRM/1
5.9 PCIe Switch
A PLX PEX8725 24-lane PCIe switch connects a x8 PCIe link from the processor to
the backplane and the XMC site. The switch is configured as follows:
Table 5-7 PCIe Switch Port Configuration
Connection
Width Port
Number
Station
Number
Comments
CPU
x8
9
1
Upstream port
XMC
x8
0
0
Backplane link A
x4
1
0
Can be aggregated into one x8 link
or four x2 links
Backplane link B
x4
2
0
LINK
For more details on the PEX8725 device, see
Link status LEDs on the rear of the board show the status of each link. See the
section for more information.
The PEX8725 PCIe switch contains DMA engines that can be used by software to
increase inter-board performance when using the Expansion Plane to connect to
other processor boards in a multi-peer PCIe system.
5.9.1
Switch Configuration EEPROM
A serial EEPROM is connected to the switch to allow the initial configuration to be
programmed by software. Write protection of this EEPROM is controlled by a BIOS
setup option, which is interlocked with the
Configuration EEPROM Write Enable
and the backplane NVMRO signal (i.e. a jumper must be fitted on the link,
and NVMRO must be low before the write protection status can be changed by the
BIOS setup option).
When the board is configured into recovery mode (a jumper is fitted on the
), the EEPROM is disabled and the switch is configured using default
strapping.
CAUTION
If third party tools such as those provided by PLX are being used to program the EEPROM, take
extreme care to ensure that erroneous values are not programmed into the EEPROM, as this
could prevent the board from booting.
NOTE
If third party tools are being used to program the EEPROM, it must still first be write-enabled by
the BIOS setup option.