Pci Target Window Enables - DEC Digital Alpha VME 4/224 User Manual

Table 5–6 PCI Target Window Enables
1
PCI_MASK<31:20>
0000 0000 0000
0000 0000 0001
0000 0000 0011
0000 0000 0111
0000 0000 1111
0000 0001 1111
0000 0011 1111
0000 0111 1111
0000 1111 1111
0001 1111 1111
0011 1111 1111
0111 1111 1111
1111 1111 1111
1
Combinations of bits not shown in PCI_MASK<31:20> are not supported.
2
Depending on the target window size, only the incoming address bits <31:n> are compared with bits
<31:n> of the PCI base registers as shown in Figure 5–4. If n = 20 to 32, no comparison is performed;
n is also used in Figure 5–6.
3
When this combination is chosen, the WENB bit in the other PCI base register must be cleared;
otherwise, the two windows will overlap.
Based on the value of the PCI mask register, the unmasked bits of the incoming
PCI address are compared with the corresponding bit of each window's PCI base
register. If the base registers and the incoming PCI address match, the incoming
PCI address has hit that target window; otherwise, it missed that window. A
window enable bit (WENB) is provided in the PCI base register of each window to
allow them to be independently enabled and disabled.
The PCI target windows must be programmed such that the PCI address ranges
do not overlap. The compare scheme between the incoming PCI address and the
PCI base register (together with the PCI mask register) is shown in Figure 5–4.
The window base addresses must be on naturally aligned address
boundaries, depending on the size of the window.
5–16 System Address Mapping
Window Size
1 MB
2 MB
4 MB
8 MB
16 MB
32 MB
64 MB
128 MB
256 MB
512 MB
1 GB
2 GB
3
4 GB
Note
2
Value of n
20
21
22
23
24
25
26
27
28
29
30
31
32