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How do I connect multiple ACE-Lite masters to a single CCI-400 ACE-Lite slave interface?

Applies to: CCI-400 Cache Coherent Interconnect, NIC-400 Network Interconnect

Answer

You can use a NIC-400 to connect multiple ACE-Lite masters to a CCI-400 slave interface. The NIC-400 is an AXI4 interconnect and does not support ACE-Lite but by using the USER signals it is possible to support the following ACE-Lite transactions:

  ARSNOOP[3:0]    ARBAR    ARDOMAIN[1:0]    Transaction
 ---------------------------------------------------------
    0b0000        0b00        0b00          ReadNoSnoop
                              0b11
 ---------------------------------------------------------
    0b0000        0b00        0b01          ReadOnce
                              0b10
 ---------------------------------------------------------

  AWSNOOP[3:0]    AWBAR    AWDOMAIN[1:0]    Transaction
 -------------------------------------------------------------
   0b0000         0b00        0b00          WriteNoSnoop
                              0b11
 -------------------------------------------------------------
   0b0000         0b00        0b01          WriteUnique
                              0b10
 -------------------------------------------------------------
   0b0001         0b00        0b01          WriteLineUnique
                              0b10
 -------------------------------------------------------------


Note: ACE-Lite is essentially AXI4 with some additional address signals, that is, AxDOMAIN, AxBAR, and AxSNOOP.

As the table shows, ARSNOOP, ARBAR, AWSNOOP[3:1], and AWBAR do not change. Therefore, these outputs from the ACE-Lite masters can be left unconnected and at the ACE-Lite slave interface on the CCI-400, they can be tied LOW.

For each ACE-Lite master, the AxDOMAIN and AWSNOOP[0] signals can connect to the USER signals and pass through the NIC-400 to the CCI-400 ACE-Lite+DVM slave interface.

On the CCI-400 ACE-Lite+DVM slave interface:

- tie ACREADY LOW
- tie CRVALID LOW
- tie all other CR channel inputs LOW.


At reset, the CCI-400 disables snoop and DVM messages for all slave interfaces. You must ensure that software does not enable snoop and DVM messages for the CCI-400 ACE-Lite+DVM slave interface.

The ACE-Lite masters must not issue barriers or cache maintenance operations because the NIC-400 does not support these features.

The NIC-400 does not support DVM messages. To perform address translations you can insert an MMU-400 between the CCI-400 and the NIC-400, so that the MMU can receive and send DVM messages.

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