indicating which stack pointer corresponds to the stack frame and what operation mode the processor
was in before the entry occurred.
If no higher-priority exception occurs during exception entry, the processor starts executing the
exception handler and automatically changes the status of the corresponding pending interrupt to
active.
If another higher-priority exception occurs during exception entry, known as late arrival, the processor
starts executing the exception handler for this exception and does not change the pending status
of the earlier exception.
2.5.7.2 Exception Return
Exception return occurs when the processor is in Handler mode and executes one of the following
instructions to load the EXC_RETURN value into the PC:
■ An LDM or POP instruction that loads the PC
■ 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 89
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
DescriptionEXC_RETURN[31:0]
Reserved0xFFFF.FFF0
Return to Handler mode.
Exception return uses state from MSP.
Execution uses MSP after return.
0xFFFF.FFF1
Reserved0xFFFF.FFF2 - 0xFFFF.FFF8
Return to Thread mode.
Exception return uses state from MSP.
Execution uses MSP after return.
0xFFFF.FFF9
Reserved0xFFFF.FFFA - 0xFFFF.FFFC
Return to Thread mode.
Exception return uses state from PSP.
Execution uses PSP after return.
0xFFFF.FFFD
Reserved0xFFFF.FFFE - 0xFFFF.FFFF
2.6 Fault Handling
Faults are a subset of the exceptions (see “Exception Model” on page 81). The following conditions
generate a fault:
■ A bus error on an instruction fetch or vector table load or a data access.
89July 24, 2012
Texas Instruments-Production Data
Stellaris
®
LM3S6G65 Microcontroller
OBSOLETE: TI has discontinued production of this device.
