Lookup Table Based Address Translation; Direct Offset Address Translation; Downstream Address Translation Example - Intel 21555 User Manual

This new base address, also called the translated base address, references a new location in the
secondary bus address map. The offset is not affected. The process is similar for transactions
forwarded from the secondary bus to the primary bus.
Figure 5. Direct Offset Address Translation
Each memory address range using direct offset address translation has its own translated base. The translated base
addresses are programmable in registers corresponding to each BAR. These registers are mapped both in
device-specific configuration space and in CSR space. The number of bits of the translated base address
corresponds to the number of writable bits in the respective BAR. Likewise, the number of bits of the offset also
varies and depends on the size of the BAR.
memory transactions. Again, upstream transactions are treated similarly.
Figure 6. Downstream Address Translation Example
Base + Offset
4.3.3

Lookup Table Based Address Translation

As mentioned in Section 4.3.2, Upstream Memory 2 address translation is treated differently than the other ranges.
The 21555 uses a page size based lookup table to perform address translation for transactions falling into this range.
A lookup table provides a flexible way of translating secondary bus local addresses to primary bus system
addresses.
21555 Non-Transparent PCI-to-PCI Bridge User Manual
Offset
Base
Offset
Translated Base
Figure 6 shows an example of address translation of downstream
Primary Address Map
Original Address
Translated Address
Secondary Address Map
Translated
Base + Offset
Address Decoding
A7463-01
A7464-01
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