Routing and Addressing Rules

There are three principal mechanisms for TLP routing: address, ID, and implicit. This section defines the rules for the address and ID routing mechanisms. Implicit routing is used only with Message Requests, and is covered in Section 2.2.8.

Address Based Routing Rules

Address routing is used with Memory and I/O Requests.
Two address formats are specified, a 64-bit format used with a 4 DW header (see Figure 2-7) and a 32-bit format used with a 3 DW header (see Figure 2-8).

Figure 2-8: 32-bit Address Routing

For Memory Read, Memory Write, and AtomicOp Requests, the Address Type (AT) field is encoded as shown in Table 2-5, with full descriptions contained in the Address Translation Services Specification, Revision 1.0. For all other Requests, the AT field is reserved.

Table 2-5: Address Type (AT) Field Encodings

 

Address mapping to the TLP header is shown in Table 2-6.

Table 2-6: Address Field Mapping

Memory Read, Memory Write, and AtomicOp Requests can use either format.
• For Addresses below 4 GB, Requesters must use the 32-bit format. The behavior of the receiver is not specified if a 64-bit format request addressing below 4 GB (i.e., with the upper 32 bits of address all 0) is received.
I/O Read Requests and I/O Write Requests use the 32-bit format.
All agents must decode all address bits in the header - address aliasing is not allowed.

ID Based Routing Rules

ID routing is used with Configuration Requests,with ID Routed Messages, and with
Completions. This specification defines Vendor_Defined Messages that are ID Routed (Section 2.2.8.6). Other specifications define additional ID Routed Messages.

ID routing uses the Bus, Device, and Function Numbers (as applicable) to specify the destination for the TLP:
• For non-ARI Routing IDs, Bus, Device, and (3-bit) Function Number to TLP header
mapping is shown in Table 2-7.
• For ARI Routing IDs, the Bus and (8-bit) Function Number to TLP header mapping is shown in Table 2-8.

Two ID routing formats are specified, one used with a 4 DW header (see Figure 2-9) and one used with a 3 DW header (see Figure 2-10).
• Header field locations are the same for both formats, and are given in Table 2-7

Table 2-7: Header Field Locations for non-ARI ID Routing

Table 2-8: Header Field Locations for ARI ID Routing

Figure 2-9: ID Routing with 4 DW Header

Figure 2-10: ID Routing with 3 DW Header