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2.2.2. TBU interfaces

The MMU-500 supports the following TBU interfaces:

ACE-Lite interfaces

The MMU-500 uses the ACE-Lite interfaces to receive and forward transactions after translation.

An AXI3 or AXI4 bus can be connected to this interface with certain limitations as described in AXI3 and AXI4 support.

When an ACE-Lite interface is used, the MMU-500 generates barrier transactions and updates attributes of input barrier transactions. Barrier transactions guarantee the ordering and observation of transactions in a system.

See the ARM® AMBA® AXI and ACE Protocol Specification AXI3, AXI4, and AXI4-Lite ACE and ACE-Lite for more information on barrier transactions.

AXI slave interface

The MMU-500 supports only the ACE-Lite slave interface for every TBU. To connect to an AXI3 or AXI4 interface, you must:

  • Tie the extra ACE-Lite signals to their inactive values.

  • Tie the sysbardisable_<tbuname> signal HIGH.

The ACE-Lite slave interface, with _s suffix, drives the untranslated address to the TBU. You must connect pin-to-pin the read address, write address, read data, write data, and buffered write response channels of the ACE-Lite slave interface, with _s suffix, to an ACE-Lite master interface. In a system, the master interface can be the AXI bus infrastructure output or the output of a bridge that converts another bus protocol to AXI.

AXI master interface

The MMU-500 supports only the ACE-Lite master interface for every TBU. You must tie the extra ACE-Lite signals to their inactive values and the sysbardisable_<tbuname> signal to HIGH to use AXI3 or AXI4 master interfaces.

The ACE-Lite master interface, with _m suffix, drives the translated address to the downstream slave. You must connect pin-to-pin the read address, write address, read data, write data, and buffered write response channels to the corresponding ACE-Lite slave interface.

If the MMU-500 is configured to support a dedicated interface for PTWs, you must connect the read address and read data channels of the slave interface associated with the PTWs to the MMU-500 PTW channel. In this configuration, the PTW channel contains the _ptw suffix. For example, araddr_ptw and acaddr_ptw.

TBU barrier support

The TBU in the MMU-500 receives, passes on, and generates barriers of its own.

The MMU-500 generates a DSBSYS barrier on its own, after ensuring that all invalidation-related transactions are initiated when sysbardisable_<tbuname> is LOW, and on receiving one of the following:

  • The SYNC message received on the programming interface.

  • The DVM SYNC message.

See the ARM® AMBA® AXI and ACE Protocol Specification AXI3, AXI4, and AXI4-Lite ACE and ACE-Lite for more information on SYNC and DVM SYNC messages.

Sideband interface

This interface provides associated information along with the ACE-Lite interface. See Sideband signals for more information.

Note

The StreamID and security state determination are associated with the ACE-Lite slave interface to each TBU.

StreamID interface

This interface is a sideband interface for the MMU-500 TBU slave interface. It provides additional information about the source of the incoming transaction. This is used to map the transaction to a particular context for translation.

The MMU-500 samples signals in the interface along with each valid address transaction.

See StreamID for more information.

Security State Determination interface

This interface is a sideband interface for the MMU-500 TBU slave interface. It provides information about the security state of a transaction.

The MMU-500 samples signals in this interface along with each valid address transaction, in a similar manner to the StreamID.

See Security determination for more information.

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