
System Address Space
A–33
PCI to Physical Memory Address
Table A–12 shows the PCI target window mask fields.
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 window
base register. If one of the window base registers and the incoming PCI address
match, then the PCI address has hit the PCI target window. Otherwise, the PCI
address has missed the window. A window enable bit, W_EN, is provided in each
window’s window base register to allow windows to be independently enabled
(W_EN = 1) or disabled (W_EN = 0).
If a hit occurs in any of the four windows that are enabled, then the 21174 will
respond to the PCI cycle by asserting the signal devsel. The PCI target windows
must be programmed so that their address ranges do not overlap; otherwise, the
results are UNDEFINED.
1
Only the incoming ad<31:n> are compared with <31:n> of the window base register, as shown in
Figure 1–18. If n=32, no comparison is performed.
Table A–12 PCI Target Window Mask Register Fields
1
PCI_MASK<31:20>
Size of Window
Value of n
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
Otherwise
UNPREDICTABLE
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