Datasheet

An embedded interrupt controller that supports low latency interrupt processing (see “Nested
Vectored Interrupt Controller (NVIC)” on page 146).
■ System Control Block (SCB)
The programming model interface to the processor. The SCB provides system implementation
information and system control, including configuration, control, and reporting of system exceptions
(see “System Control Block (SCB)” on page 147).
■ Memory Protection Unit (MPU)
Improves system reliability by defining the memory attributes for different memory regions. The
MPU provides up to eight different regions and an optional predefined background region (see
“Memory Protection Unit (MPU)” on page 147).
■ Floating-Point Unit (FPU)
Fully supports single-precision add, subtract, multiply, divide, multiply and accumulate, and
square-root operations. It also provides conversions between fixed-point and floating-point data
formats, and floating-point constant instructions (see “Floating-Point Unit (FPU)” on page 152).
2.3 Programming Model
This section describes the Cortex-M4F programming model. In addition to the individual core register
descriptions, information about the processor modes and privilege levels for software execution and
stacks is included.
2.3.1 Processor Mode and Privilege Levels for Software Execution
The Cortex-M4F has two modes of operation:
■ Thread mode
Used to execute application software. The processor enters Thread mode when it comes out of
reset.
■ Handler mode
Used to handle exceptions. When the processor has finished exception processing, it returns to
Thread mode.
In addition, the Cortex-M4F has two privilege levels:
■ Unprivileged
In this mode, software has the following restrictions:
– Limited access to the MSR and MRS instructions and no use of the CPS instruction
– No access to the system timer, NVIC, or system control block
– Possibly restricted access to memory or peripherals
■ Privileged
In this mode, software can use all the instructions and has access to all resources.
In Thread mode, the CONTROL register (see page 108) controls whether software execution is
privileged or unprivileged. In Handler mode, software execution is always privileged.
93December 13, 2013
Texas Instruments-Advance Information
Tiva
™
TM4C129XNCZAD Microcontroller