Atmel Xplained Evaluation Board AT32UC3A3-XPLD AT32UC3A3-XPLD 数据表

32072H–AVR32–10/2012

At the end of the current access, if no other request is pending, the slave remains connected to
its associated default master. A slave can be associated with three kinds of default masters: no
default master, last access master and fixed default master.

At the end of the current access, if no other request is pending, the slave is disconnected from
all masters. No Default Master suits low-power mode.

At the end of the current access, if no other request is pending, the slave remains connected to
the last master that performed an access request.

At the end of the current access, if no other request is pending, the slave connects to its fixed
default master. Unlike last access master, the fixed master does not change unless the user
modifies it by a software action (field FIXED_DEFMSTR of the related SCFG).

To change from one kind of default master to another, the Bus Matrix user interface provides the
Slave Configuration Registers, one for each slave, that set a default master for each slave. The
Slave Configuration Register contains two fields: DEFMSTR_TYPE and FIXED_DEFMSTR. The
2-bit DEFMSTR_TYPE field selects the default master type (no default, last access master, fixed
default master), whereas the 4-bit FIXED_DEFMSTR field selects a fixed default master pro-
vided that DEFMSTR_TYPE is set to fixed default master. Please refer to the Bus Matrix user
interface description.

The Bus Matrix provides an arbitration mechanism that reduces latency when conflict cases
occur, i.e. when two or more masters try to access the same slave at the same time. One arbiter
per HSB slave is provided, thus arbitrating each slave differently.

The Bus Matrix provides the user with the possibility of choosing between 2 arbitration types for
each slave:

1.

Round-Robin Arbitration (default)

2.

Fixed Priority Arbitration

This choice is made via the field ARBT of the Slave Configuration Registers (SCFG).

Each algorithm may be complemented by selecting a default master configuration for each
slave.

When a re-arbitration must be done, specific conditions apply. See 

Each arbiter has the ability to arbitrate between two or more different master requests. In order
to avoid burst breaking and also to provide the maximum throughput for slave interfaces, arbitra-
tion may only take place during the following cycles:

1.

Idle Cycles: When a slave is not connected to any master or is connected to a master 
which is not currently accessing it.

2.

Single Cycles: When a slave is currently doing a single access.