LM3S2B93 Datasheet, PDF (104/1194 Pages) Texas Instruments – Stellaris® LM3S2B93 Microcontroller

The Cortex-M3 Processor
2.6
2.6.1
■ A BX instruction using any register
■ An LDR instruction with the PC as the destination
EXC_RETURN is the value loaded into the LR on exception entry. The exception mechanism relies
on this value to detect when the processor has completed an exception handler. The lowest four
bits of this value provide information on the return stack and processor mode. Table 2-10 on page 104
shows the EXC_RETURN values with a description of the exception return behavior.
EXC_RETURN bits 31:4 are all set. When this value is loaded into the PC, it indicates to the processor
that the exception is complete, and the processor initiates the appropriate exception return sequence.
Table 2-10. Exception Return Behavior
EXC_RETURN[31:0]
0xFFFF.FFF0
0xFFFF.FFF1
0xFFFF.FFF2 - 0xFFFF.FFF8
0xFFFF.FFF9
0xFFFF.FFFA - 0xFFFF.FFFC
0xFFFF.FFFD
0xFFFF.FFFE - 0xFFFF.FFFF
Description
Reserved
Return to Handler mode.
Exception return uses state from MSP.
Execution uses MSP after return.
Reserved
Return to Thread mode.
Exception return uses state from MSP.
Execution uses MSP after return.
Reserved
Return to Thread mode.
Exception return uses state from PSP.
Execution uses PSP after return.
Reserved
Fault Handling
Faults are a subset of the exceptions (see “Exception Model” on page 96). The following conditions
generate a fault:
■ A bus error on an instruction fetch or vector table load or a data access.
■ An internally detected error such as an undefined instruction or an attempt to change state with
a BX instruction.
■ Attempting to execute an instruction from a memory region marked as Non-Executable (XN).
■ An MPU fault because of a privilege violation or an attempt to access an unmanaged region.
Fault Types
Table 2-11 on page 104 shows the types of fault, the handler used for the fault, the corresponding
fault status register, and the register bit that indicates the fault has occurred. See page 159 for more
information about the fault status registers.
Table 2-11. Faults
Fault
Bus error on a vector read
Handler
Hard fault
Fault Status Register
Hard Fault Status (HFAULTSTAT)
Bit Name
VECT
104
January 20, 2012
Texas Instruments-Production Data