Digi NS9215 manual M a i n a c c e s s c o n t r o l, Compatibility issues

Models: NS9215

1 517
Download 517 pages 25.29 Kb
Page 121
Image 121

Compatibility issues

WO R K I N G W I T H T H E C P U

. .

 

Domain access control..

 

.

Domain

Fault Address register

 

 

Domain

MVA of first aborted address in transfer

 

 

Permission

MVA of first aborted address in transfer

 

 

External about for noncached reads,

MVA of last address before 1KB boundary, if any word of

or nonbuffered writes

the transfer before 1 KB boundary is externally aborted.

 

MVA of last address in transfer if the first externally

 

aborted word is after the 1 KB boundary.

 

 

To enable code to be ported easily to future architectures, it is recommended that no reliance is made on external abort behavior.

The Instruction Fault Status register is intended for debugging purposes only.

D o m a i n a c c e s s c o n t r o l

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Specifying access permissions

MMU accesses are controlled primarily through the use of domains. There are 16 domains, and each has a two-bit field to define access to it. Client users and Manager users are supported.

The domains are defined in the R3: Domain Access Control register; the register format in “R3:Domain Access Control register” on page 91 shows how the 32 bits of the register are allocated to define the 16 two-bit domains.

This table shows how the bits within each domain are defined to specify access permissions.

Value

Meaning

Description

 

 

 

0 0

No access

Any access generates a domain fault.

 

 

 

0 1

Client

Accesses are checked against the access permission bits in the section or

 

 

page descriptor.

 

 

 

1 0

Reserved

Reserved. Currently behaves like no access mode.

 

 

 

1 1

Manager

Accesses are not checked against the access permission bits, so a

 

 

permission fault cannot be generated.

 

 

 

Interpreting access permission bits

This table shows how to interpret the access permission (AP) bits, and how the interpretation depends on the R and S bits in the R1: Control register (see "R1: Control register," beginning on page 88).

www.digiembedded.com

121

Page 121
Image 121
Digi NS9215 manual M a i n a c c e s s c o n t r o l, Compatibility issues, Specifying access permissions