Table 19-1. How the Crossbar Switch grants control of a slave port to a master (continued)
When Then the Crossbar Switch grants control to the
requesting master
• The current master is running an undefined length burst
transfer.
• The requesting master's priority level is higher than that
of the current master.
The requesting master's priority level is lower than the current
master.
At the conclusion of one of the following cycles:
• An IDLE cycle
• A non-IDLE cycle to a location other than the current
slave port
19.3.2.2 Round-robin priority operation
When operating in round-robin mode, each master is assigned a relative priority based on
the master port number. This relative priority is compared to the master port number (ID)
of the last master to perform a transfer on the slave bus. The highest priority requesting
master becomes owner of the slave bus at the next transfer boundary. Priority is based on
how far ahead the ID of the requesting master is to the ID of the last master.
After granted access to a slave port, a master may perform as many transfers as desired to
that port until another master makes a request to the same slave port. The next master in
line is granted access to the slave port at the next transfer boundary, or possibly on the
next clock cycle if the current master has no pending access request.
As an example of arbitration in round-robin mode, assume the crossbar is implemented
with master ports 0, 1, 4, and 5. If the last master of the slave port was master 1, and
master 0, 4, and 5 make simultaneous requests, they are serviced in the order: 4 then 5
then 0.
The round-robin arbitration mode generally provides a more fair allocation of the
available slave-port bandwidth (compared to fixed priority) as the fixed master priority
does not affect the master selection.
19.4
Initialization/application information
No initialization is required for the crossbar switch. See the chip-specific crossbar switch
information for the reset state of the arbitration scheme.
Initialization/application information
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
410 NXP Semiconductors
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