User guide

Figure 5–4 PCI Target Window Compare Scheme
LJ-03955.AI
31
nn 20 19 13 12 00
31 nn 20
Offset
Hit
XXX
Compare
Peripheral Page NumberPCI Address
PCI Base
Register
31 nn
-1
-1
-1 20
111 (Determines ) n 0000000
PCI Mask
Register
When an address match occurs with a PCI target window, the 21071-DA
translates the 32-bit PCI address ad<31:0> to a 34-bit processor byte address
(actually a 29-bit hexword address). The translated address is generated in one of
two ways as determined by the scatter-gather enable (SGEN) bit of the PCI base
register of the associated window.
If SGEN is cleared, the DMA address is direct mapped. The translated address
is generated by concatenating bits from the matching window translated base
register with bits from the incoming PCI address. The PCI mask register
determines which bits of the translated base register and PCI address are used to
generate the translated address as shown in Table 5–7.
The unused bits of the translated base register must be cleared for correct
operation. Because system memory is located in the lower half of the CPU
address space, bit sysBus<33> is always zero. Bits sysBus<32:5> are obtained
from the translated base register.
System Address Mapping 5–17