Software Architecture
PLX Technology, Inc.
7.3.1
Switch Device Number Assignment Example
The following is an example of how to access the PEX 8532’s upstream port and downstream ports.
Assume that the PEX 8532 consists of seven ports, with one x8 upstream (default is Port 0) and six x4
downstream ports (Ports 1, 2, 8, 9, 10, 11). Further assume that the upstream Bus Number is 1, and that
each downstream port uses only one Bus Number, and that bus numbering is linear.
A diagram of the system is illustrated in Figure 7-2.
• The upstream port (which is configured as Port 0 with 8 lanes for this example), by default,
and is assigned a primary Bus Number of 1 and a secondary Bus Number of 2. With five of
the downstream ports each having one bus and a sixth downstream port having two buses, the
Subordinate Bus Number is 2 + (5 * 1) + (1 * 2) = 9. The Device Number, regardless of which
port is the upstream port, is always 00h.
• Port 1 registers are accessed with a Type 1 Configuration transaction:
– Bus Number is the internal Virtual PCI Bus (upstream port Secondary Bus Number, 2)
– Device Number is 01h
– Function Number to be 000b
• Port 2 registers are accessed with a Type 1 Configuration transaction:
– Bus Number is 2
– Device Number is 02h
– Function Number is 000b
• Port 3 registers cannot be accessed. A Configuration access to this port returns
an “Unsupported Request” (UR) error.
• Port 8 registers are accessed with a Type 1 Configuration transaction:
– Bus Number is 2
– Device Number is 08h
– Function Number is 000b
• Port 9 registers are accessed with a Type 1 Configuration transaction:
– Bus Number is 2
– Device Number is 09h
– Function Number is 000b
• Port 10 registers are accessed with a Type 1 Configuration transaction:
– Bus Number is 2
– Device Number is 0Ah
– Function Number is 000b
• Port 11 registers are accessed with a Type 1 Configuration transaction:
– Bus Number is 2
– Device Number is 0Bh
– Function Number is 000b
90
ExpressLane PEX 8532AA/BA/BB/BC 8-Port/32-Lane Versatile PCI Express Switch Data Book
Copyright © 2007 by PLX Technology, Inc. All Rights Reserved – Version 1.6
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