Datasheet

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.
2.3.2 Stacks
The processor uses a full descending stack, meaning that the stack pointer indicates the last stacked
item on the 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 processor implements two stacks:
the main stack and the process stack, with a pointer for each held in independent registers (see the
SP register on page 95).
In Thread mode, the CONTROL register (see page 105) controls whether the processor uses the
main stack or the process stack. In Handler mode, the processor always uses the main stack. The
options for processor operations are shown in Table 2-1 on page 91.
Table 2-1. Summary of Processor Mode, Privilege Level, and Stack Use
Stack UsedPrivilege LevelUseProcessor Mode
Main stack or process stack
a
Privileged or unprivileged
a
ApplicationsThread
Main stackAlways privilegedException handlersHandler
a. See CONTROL (page 105).
2.3.3 Register Map
Figure 2-3 on page 92 shows the Cortex-M4F register set. Table 2-2 on page 92 lists the Core
registers. The core registers are not memory mapped and are accessed by register name, so the
base address is n/a (not applicable) and there is no offset.
91June 18, 2014
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