ARM AMBA NIC-301 用户手册

ARM DDI 0397G

2-17

ID031010

When you configure a write data FIFO of at least 4, you can also set an additional write tidemark 
function, named 

wr_tidemark

. This is a tidemark level that stalls the release of the transaction 

until:
•

The network receives the WLAST beat.

•

The write FIFO becomes full.

•

The number of occupied slots in the write data FIFO exceeds the write tidemark. See 
Chapter 3 Programmers Model.

You can program the arbitration algorithm for all arbitration nodes within the infrastructure.

At the entry point to the infrastructure, all transactions are allocated a local QoS that you can 
configure to be:
•

static

•

programmable

•

received from the attached master, for AXI only.

The arbitration of the transaction throughout the infrastructure uses this QoS. See Chapter 3 
Programmers Model.

At any arbitration node, a fixed priority exists for transactions with a different QoS. The highest 
value has the highest priority. If there are coincident transactions at an arbitration node with the 
same QoS that require arbitration, then the Network uses a Least Recently Used (LRU) 
algorithm.

Because the AXI protocol permits re-ordering of transactions, it might be necessary for the 
AMBA Network Interconnect to enforce rules to prevent deadlock when routing multiple 
transactions concurrently to multiple slaves from a single point of divergence, that is, at a switch 
slave interface.

Each slave interface of a switch can have a different CDAS configured. The same CDAS 
scheme is configured for both read and write transactions, but they operate independently.

This section describes:
•

•

This ensures that at a slave interface of a switch:
•

all outstanding read transactions are to a single end destination

•

all outstanding write transactions are to a single end destination.

If the slave interface receives a transaction to a different destination to the current destination 
for that transaction type, the network stalls the transactions until all the outstanding transactions 
of that type have been completed.

This ensures that at a slave interface of a switch:
•

all outstanding read transactions with the same ID go the same destination