Atmel Xplained Evaluation Board AT32UC3L0-XPLD AT32UC3L0-XPLD Data Sheet
Product codes
AT32UC3L0-XPLD
24
32099G–06/2011
AT32UC3L016/32/64
Figure 4-5.
The Status Register Low Halfword
4.4.3
Processor States
4.4.3.1
Normal RISC State
.
Mode changes can be made under software control, or can be caused by external interrupts or
exception processing. A mode can be interrupted by a higher priority mode, but never by one
with lower priority. Nested exceptions can be supported with a minimal software overhead.
exception processing. A mode can be interrupted by a higher priority mode, but never by one
with lower priority. Nested exceptions can be supported with a minimal software overhead.
When running an operating system on the AVR32, user processes will typically execute in the
application mode. The programs executed in this mode are restricted from executing certain
instructions. Furthermore, most system registers together with the upper halfword of the status
register cannot be accessed. Protected memory areas are also not available. All other operating
modes are privileged and are collectively called System Modes. They have full access to all priv-
ileged and unprivileged resources. After a reset, the processor will be in supervisor mode.
application mode. The programs executed in this mode are restricted from executing certain
instructions. Furthermore, most system registers together with the upper halfword of the status
register cannot be accessed. Protected memory areas are also not available. All other operating
modes are privileged and are collectively called System Modes. They have full access to all priv-
ileged and unprivileged resources. After a reset, the processor will be in supervisor mode.
4.4.3.2
Debug State
The AVR32 can be set in a debug state, which allows implementation of software monitor rou-
tines that can read out and alter system information for use during application development. This
implies that all system and application registers, including the status registers and program
counters, are accessible in debug state. The privileged instructions are also available.
tines that can read out and alter system information for use during application development. This
implies that all system and application registers, including the status registers and program
counters, are accessible in debug state. The privileged instructions are also available.
All interrupt levels are by default disabled when debug state is entered, but they can individually
be switched on by the monitor routine by clearing the respective mask bit in the status register.
be switched on by the monitor routine by clearing the respective mask bit in the status register.
Bit 15
Bit 0
Reserved
Carry
Zero
Sign
Zero
Sign
0
0
0
0
0
0
0
0
0
0
0
0
0
0
-
-
-
-
T
-
Bit name
Initial value
0
0
L
Q
V
N
Z
C
-
Overflow
Saturation
Saturation
-
-
-
Lock
Reserved
Scratch
Table 4-2.
Overview of Execution Modes, their Priorities and Privilege Levels.
Priority
Mode
Security Description
1
Non Maskable Interrupt
Privileged
Non Maskable high priority interrupt mode
2
Exception
Privileged
Execute exceptions
3
Interrupt 3
Privileged
General purpose interrupt mode
4
Interrupt 2
Privileged
General purpose interrupt mode
5
Interrupt 1
Privileged
General purpose interrupt mode
6
Interrupt 0
Privileged
General purpose interrupt mode
N/A
Supervisor
Privileged
Runs supervisor calls
N/A
Application
Unprivileged
Normal program execution mode