Atmel AT32UC3A3128, Manual

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32072H–AVR32–10/2012
AT32UC3A3
Figure 4-5. The Status Register Low Halfword
4.4.3 Processor States
4.4.3.1 Normal RISC State
The AVR32 processor supports several different execution contexts as shown in Table 4-2 on
page 27 .
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.
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.
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.
Bit 15 Bit 0
Reserved
Carry
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
- - -
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