Specifications

9 March 1999 – Subject To Change 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.
Table A–12 PCI Target Window Mask Register Fields
1
1
Only the incoming ad<31:n> are compared with <31:n> of the window base register, as shown in
Figure A–18. If n=32, no comparison is performed.
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 —