2-5
Themis Computer
2—2P2 PMC/XMC Carrier Board
2P2 PMC/XMC Carrier Board Overview
The 2P2 PMC/XMC allows you to configure both the primary and secondary bus
interfaces for one of four possible modes: 5V/33MHz, 3.3V/33MHz, 5V/66MHz, or
3.3V/66MHz. You configure the mode by setting solder beads SB87 and SB88 (volt-
age setting) and SB69 and SB70 (frequency setting) (see
Table 2-9
on page 2-20).
Note that the default mode for both interfaces is 5V/66MHz.
The 21154 provides full support for delayed transactions, which enables the buffer-
ing of memory read, I/O, and configuration transactions. The 21154 has separate
posted write, read data, and delayed transaction queues with significant buffering
capability. In addition, the 21154 supports buffering of simultaneous, multiple,
posted write, and delayed transactions in both directions.
For more information about the PCI-to-PCI interface refer to the hardware and soft-
ware manuals for your particular Themis system (for example, the TA64, TP32, et al.).
2.1.2
The PCI Express Switch
The 2P2 PMC/XMC Carrier Board offers PCI Express technology for PCI Express aggre-
gation, employing a PEX8516 device from PLX Technology (P/N 8516AA-25BI G). The
device has four ports that can be configured for x1, x2, x4 or x8 bus widths.
As shown in
Figure 2-4
, the PEX8516 Switch aggregates two 4-lane PCI Express
buses from the PMC/XMC slots into one PCI Express 8-lane bus to the baseboard.
Configuration data for the PCI Express Switch is stored in an on-board EEPROM.
Upon initialization, information will be transferred from the EEPROM to the PCI
Switch in order to initialize all of the registers on the PEX8516.
Figure 2-4.
PCI Express Aggregation using a PCI Express Switch
x8
x4
x4
PCI Express
Switch
(PEX8516)
XMC Slot 1
XMC Slot 2
PCI Express to
Baseboard
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