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38 21555 Non-Transparent PCI-to-PCI Bridge User Manual
Address Decoding
The Upstream Memory 2 address range consists of a fixed number (64) of pages. The page size is
programmable in the Chip Control 1 configuration register. Therefore, the size of the Upstream
Memory 2 BAR is dependent on the page size. The page size varies between 256 bytes to 32 MB
by powers of 2. This results in a window size that varies from 16 KB to 2 GB. This BAR can also
be disabled.
Each page of the upstream window has a corresponding translated base address.
The size of the translated base address varies with the page size and window size. The translated base address
replaces both the original base address and the lookup table index bits. The address bits used for the original base
address for a given page and window size are listed in Table 11, as well as the locations of the six address bits
needed to select one of the 64 entries in the lookup table. The offset of the address, which is not translated, consists
of the remaining lower order address bits. Table 11 shows the Upstream Memory 2 window size, with base address,
index, and offset fields.
Table 11. Upstream Memory 2 Window Size
Page Size
(bytes)
Window Size
(bytes)
Base Address
(bits)
Lookup Table Index
(bits)
Offset
(bits)
256 16K [31:14] [13:8] [7:0]
512 32K [31:15] [14:9] [8:0]
1K 64K [31:16] [15:10] [9:0]
2K 128K [31:17] [16:11] [10:0]
4K 256K [31:18] [17:12] [11:0]
8K 512K [31:19] [18:13] [12:0]
16K 1M [31:20] [19:14] [13:0]
32K 2M [31:21] [20:15] [14:0]
64K 4M [31:22] [21:16] [15:0]
128K 8M [31:23] [22:17] [16:0]
256K 16M [31:24] [23:18] [17:0]
512K 32M [31:25] [24:19] [18:0]
1M 64M [31:26] [25:20] [19:0]
2M 128M [31:27] [26:21] [20:0]
4M 256M [31:28] [27:22] [21:0]
8M 512M [31:29] [28:23] [22:0]
16M 1G [31:30] [29:24] [23:0]
32 2G [31] [30:25] [24:0]