Specifications

A–30 System Address Mapping
Subject to Change – 17 January 1997
PCI-to-Physical Memory Addressing
Based on the value of the window mask register, the unmasked bits of the incoming
PCI address are compared with the corresponding bits of each window’s Wn_BASE.
If the address in one of the Wn_BASE registers and the incoming PCI address
match, then the PCI address has hit that PCI target window. Otherwise, it has missed
the window.
A window enable bit, Wn_BASE [W_EN], allows windows to be independently
enabled ([W_EN]=1) or disabled ([W_EN]=0). If a hit occurs in any of the windows
that are enabled, the CIA will respond to the PCI cycle by asserting devsel_l. The
PCI target windows must be programmed so that their address ranges do not overlap.
If they overlap, the compare results are UNDEFINED.
The window base address must be on a NATURALLY ALIGNED address boundary
corresponding to the size of the window. For example, a 4MB window cannot start at
address 1MB; it must start at address 4MB, or 8MB, or 12MB, and so on.
1
Only incoming
ad<31:
n
>
are compared with PCI base register <31:n> as shown in Figure A–15. If
n=32, no comparison is performed. Windows are not allowed to overlap.
Table A–10 PCI Target Window MASK Register (W
n
_MASK)
W_MASK<31:20> Size of Window Value of
n
1
0000 0000 0000 1MB 20
0000 0000 0001 2MB 21
0000 0000 0011 4MB 22
0000 0000 0111 8MB 23
0000 0000 1111 16MB 24
0000 0001 1111 32MB 25
0000 0011 1111 64MB 26
0000 0111 1111 128MB 27
0000 1111 1111 256MB 28
0001 1111 1111 512MB 29
0011 1111 1111 1GB 30
0111 1111 1111 2GB 31
1111 1111 1111 4GB 32
All others UNPREDICTABLE
–