Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet

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SAM4S Series [DATASHEET]

Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14

 gives valid paths for master to slave access on Matrix 0. The paths shown as “-” are forbidden or not 

wired, e.g. access from the Cortex-M4 S Bus to the internal ROM. 

The Bus Matrix provides one decoder for every AHB master interface. The decoder offers each AHB master 

several memory mappings. In fact, depending on the product, each memory area may be assigned to several 

slaves. Thus it is possible to boot at the same address while using different AHB slaves.

The Bus Matrix provides some speculative bus granting techniques in order to anticipate access requests from 

some masters. This technique reduces latency at the first access of a burst or single transfer. Bus granting sets a 

default master for every slave. 
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 one of the three implementations of default masters: 



No default master



Last access master



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 the last access master, the fixed master does not change unless the user modifies it by software (field 

FIXED_DEFMSTR of the related MATRIX_SCFG).
To change from one kind of default master to another, the Bus Matrix user interface provides the Slave 

Configuration registers (MATRIX_SCFGx), one for each slave, used to set a default master for each slave. 

MATRIX_SCFGx contains the fields DEFMSTR_TYPE and FIXED_DEFMSTR. The 2-bit DEFMSTR_TYPE field 

Slaves

Masters

0 1

 

2

3

0

Internal SRAM

–

X

X

X

1

Internal ROM

X

–

X

X

2

Internal Flash

X

–

-

X

3

External Bus Interface

–

X

X

X

4

 Peripheral Bridge

–

X

X

–