Datasheet

845
32142D–06/2013
ATUC64/128/256L3/4U
34.2.2 SAB Security Restrictions
The Service Access bus can be restricted by internal security measures. A short description of
the security measures are found in the table below.
34.2.2.1 Security measure and control location
A security measure is a mechanism to either block or allow SAB access to a certain address or
address range. A security measure is enabled or disabled by one or several control signals. This
is called the control location for the security measure.
These security measures can be used to prevent an end user from reading out the code pro-
grammed in the flash, for instance.
Below follows a more in depth description of what locations are accessible when the security
measures are active.
Note: 1. Second Word of the User Page, refer to the Fuses Settings section for details.
HSB 0x5
Alternative mapping for HSB space, for compatibility with
other 32-bit AVR devices.
Memory Service
Unit
0x6 Memory Service Unit registers
Reserved Other Unused
Table 34-1. SAB Slaves, Addresses and Descriptions
Slave Address [35:32] Description
Table 34-2. SAB Security Measures
Security Measure Control Location Description
Secure mode
FLASHCDW
SECURE bits set
Allocates a portion of the flash for secure code. This code
cannot be read or debugged. The User page is also locked.
Security bit
FLASHCDW
security bit set
Programming and debugging not possible, very restricted
access.
User code
programming
FLASHCDW
UPROT + security
bit set
Restricts all access except parts of the flash and the flash
controller for programming user code. Debugging is not
possible unless an OS running from the secure part of the
flash supports it.
Table 34-3. Secure Mode SAB Restrictions
Name Address Start Address End Access
Secure flash area 0x580000000
0x580000000 +
(USERPAGE[15:0] << 10)
Blocked
Secure RAM area 0x500000000
0x500000000 +
(USERPAGE[31:16] << 10)
Blocked
User page 0x580800000 0x581000000 Read
Other accesses - - As normal