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ColdFire Core
MCF5213 ColdFire® Integrated Microcontroller Reference Manual, Rev. 3
3-12
Freescale Semiconductor
3.5
Processor Exceptions
3.5.1
Access Error Exception
The exact processor response to an access error depends on the memory reference being performed. For
an instruction fetch, the processor postpones the error reporting until the faulted reference is needed by an
instruction for execution. Therefore, faults during instruction prefetches followed by a change of
instruction flow do not generate an exception. When the processor attempts to execute an instruction with
a faulted opword and/or extension words, the access error is signaled and the instruction aborted. For this
type of exception, the programming model has not been altered by the instruction generating the access
error.
If the access error occurs on an operand read, the processor immediately aborts the current instruction’s
execution and initiates exception processing. In this situation, any address register updates attributable to
the auto-addressing modes, (for example, (An)+,-(An)), have already been performed, so the programming
model contains the updated An value. In addition, if an access error occurs during a MOVEM instruction
loading from memory, any registers already updated before the fault occurs contain the operands from
memory.
The V2 ColdFire processor uses an imprecise reporting mechanism for access errors on operand writes.
Because the actual write cycle may be decoupled from the processor’s issuing of the operation, the
signaling of an access error appears to be decoupled from the instruction that generated the write.
Accordingly, the PC contained in the exception stack frame merely represents the location in the program
when the access error was signaled. All programming model updates associated with the write instruction
are completed. The NOP instruction can collect access errors for writes. This instruction delays its
execution until all previous operations, including all pending write operations, are complete. If any
previous write terminates with an access error, it is guaranteed to be reported on the NOP instruction.
3.5.2
Address Error Exception
Any attempted execution transferring control to an odd instruction address (that is, if bit 0 of the target
address is set) results in an address error exception.
Any attempted use of a word-sized index register (Xn.w) or a scale factor of eight on an indexed effective
addressing mode generates an address error, as does an attempted execution of a full-format indexed
addressing mode, which is defined by bit 8 of extension word 1 being set.
If an address error occurs on a JSR instruction, the Version 2 ColdFire processor calculates the target
address then the return address is pushed onto the stack. If an address error occurs on an RTS instruction,
the Version 2 ColdFire processor overwrites the faulting return PC with the address error stack frame.
3.5.3
Illegal Instruction Exception
Recall the ColdFire variable-length instruction set architecture supports three instruction sizes: 16, 32, or
48 bits. The first instruction word is known as the operation word (or opword), while the optional words
are known as extension word 1 and extension word 2. The opword is further subdivided into three sections:
the upper four bits segment the entire ISA into 16 instruction lines, the next 6 bits define the operation
Содержание ColdFire MCF5211
Страница 48: ...Overview MCF5213 ColdFire Integrated Microcontroller Reference Manual Rev 3 1 14 Freescale Semiconductor...
Страница 158: ...Reset Controller Module MCF5213 ColdFire Integrated Microcontroller Reference Manual Rev 3 9 10 Freescale Semiconductor...
Страница 218: ...Edge Port Module EPORT MCF5213 ColdFire Integrated Microcontroller Reference Manual Rev 3 13 8 Freescale Semiconductor...
Страница 234: ...DMA Controller Module MCF5213 ColdFire Integrated Microcontroller Reference Manual Rev 3 14 16 Freescale Semiconductor...
Страница 378: ...I2 C Interface MCF5213 ColdFire Integrated Microcontroller Reference Manual Rev 3 22 16 Freescale Semiconductor...
Страница 468: ...FlexCAN MCF5213 ColdFire Integrated Microcontroller Reference Manual Rev 3 25 30 Freescale Semiconductor...