ATSAM3U-EK Atmel, ATSAM3U-EK Datasheet - Page 58

• Manufacturer Part Number: ATSAM3U-EK
• Description: KIT EVAL FOR AT91SAM3U CORTEX
• Manufacturer: Atmel
• Type: MCUr

Specifications of ATSAM3U-EK

• Contents: Board
• Processor To Be Evaluated: SAM3U
• Data Bus Width: 32 bit
• Interface Type: RS-232, USB
• Operating Supply Voltage: 3 V
• Silicon Manufacturer: Atmel
• Core Architecture: ARM
• Core Sub-architecture: Cortex - M3
• Silicon Core Number: SAM3U4E
• Silicon Family Name: SAM3U
• Kit Contents: Board CD Docs
• Rohs Compliant: Yes
• For Use With/related Products: AT91SAM3U
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

13.3.1.4
13.3.2
58
SAM3U Series
Stacks
Privileged
Unprivileged software executes at the unprivileged level.
The software can use all the instructions and has access to all resources.
Privileged software executes at the privileged level.
In Thread mode, the CONTROL register controls whether software execution is privileged or
unprivileged, see
always privileged.
Only privileged software can write to the CONTROL register to change the privilege level for
software execution in Thread mode. Unprivileged software can use the SVC instruction to make
a supervisor call to transfer control to privileged software.
The processor uses a full descending stack. This means the stack pointer indicates the last
stacked item on the stack memory. When the processor pushes a new item onto the stack, it
decrements the stack pointer and then writes the item to the new memory location. The proces-
sor implements two stacks, the main stack and the process stack, with independent copies of
the stack pointer, see
In Thread mode, the CONTROL register controls whether the processor uses the main stack or
the process stack, see
uses the main stack. The options for processor operations are:
Table 13-1.
1.
Processor
mode
Thread
Handler
• cannot access the system timer, NVIC, or system control block
• might have restricted access to memory or peripherals.
See
“CONTROL register” on page
Summary of processor mode, execution privilege level, and stack use options
Used to
execute
Applications
Exception
handlers
“CONTROL register” on page
“Stack Pointer” on page
“CONTROL register” on page
Privilege level for
software execution
Privileged or
unprivileged
Always privileged
67.
(1)
60.
67. In Handler mode, software execution is
67. In Handler mode, the processor always
Stack used
Main stack or process
stack
Main stack
(1)
6430D–ATARM–25-Mar-11