Address Decode - 2.1 English

AXI Interconnect LogiCORE IP Product Guide (PG059)

Document ID
PG059
Release Date
2022-05-17
Version
2.1 English

The AXI Crossbar core must determine which MI slot is the target of each transaction by decoding the address of each AW and AR channel transaction from the SI slots. This address decode involves only those upper-order address bits needed to distinguish between MI slots and ignores lower-order bits that might be used to distinguish locations within the connected slave device. The entire address value received from the SI is presented to the MI and made available to the slave device. It is visible to any connected monitors, even though the high-order address bits are typically not reused by the slave device.

In some cases, there might be multiple, possibly disjoint, address ranges that define when a single slave device (MI slot) is accessed. The address decode logic in the AXI Crossbar core includes the multiple ranges that determine selection of each MI slot. Differentiation between the multiple address ranges is also typically required by the functionality of the connected slave device.

Whenever a transaction address received on the SI does not match any of the ranges being decoded by the AXI Crossbar core, the transaction is trapped and handled by a decode error module within the AXI Crossbar core. The Crossbar generates a protocol-compliant response back to the originating master with the decoder error (DECERR) response code. The offending transaction is not seen by any connected slave.

 

IMPORTANT:   All range sizes must be a power of 2. The base address of all ranges must be aligned to (integer multiple of) its size. There must be no overlap among all address ranges across all MI slots configured in the AXI Crossbar. (These rules are enforced by the tools.) AXI Crossbar does not support address remapping.

The Crossbar IP contains one address map table used to decode the addresses received on all SI slots. If you need to restrict any connected master device so that it does not have access to the entire address range of any connected slave device, then insert the AXI memory management unit (MMU) IP to configure address ranges specific to each master.