Datasheet

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SAM9263 [DATASHEET]
Atmel-6249N-ATARM-SAM9263-Datasheet_14-Mar-16
19.4.2 Round-Robin Arbitration
This algorithm allows the Bus Matrix arbiters to dispatch the requests from different masters to the same slave in a
round-robin manner. If two or more master’s requests arise at the same time, the master with the lowest number is
first serviced then the others are serviced in a round-robin manner.
There are three round-robin algorithm implemented:
 Round-Robin arbitration without default master
 Round-Robin arbitration with last access master
 Round-Robin arbitration with fixed default master
19.4.2.1 Round-Robin Arbitration without Default Master
This is the main algorithm used by Bus Matrix arbiters. It allows the Bus Matrix to dispatch requests from different
masters to the same slave in a pure round-robin manner. At the end of the current access, if no other request is
pending, the slave is disconnected from all masters. This configuration incurs one latency cycle for the first access
of a burst. Arbitration without default master can be used for masters that perform significant bursts.
19.4.2.2 Round-Robin Arbitration with Last Access Master
This is a biased round-robin algorithm used by Bus Matrix arbiters. It allows the Bus Matrix to remove the one
latency cycle for the last master that accessed the slave. In fact, at the end of the current transfer, if no other
master request is pending, the slave remains connected to the last master that performs the access. Other non
privileged masters will still get one latency cycle if they want to access the same slave. This technique can be used
for masters that mainly perform single accesses.
19.4.2.3 Round-Robin Arbitration with Fixed Default Master
This is another biased round-robin algorithm, it allows the Bus Matrix arbiters to remove the one latency cycle for
the fixed default master per slave. At the end of the current access, the slave remains connected to its fixed default
master. Every request attempted by this fixed default master will not cause any latency whereas other non
privileged masters will still get one latency cycle. This technique can be used for masters that mainly perform
single accesses.
19.4.3 Fixed Priority Arbitration
This algorithm allows the Bus Matrix arbiters to dispatch the requests from different masters to the same slave by
using the fixed priority defined by the user. If two or more master’s requests are active at the same time, the
master with the highest priority number is serviced first. If two or more master’s requests with the same priority are
active at the same time, the master with the highest number is serviced first.
For each slave, the priority of each master may be defined through the Priority Registers for Slaves
(MATRIX_PRAS and MATRIX_PRBS).