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MC68340AB16E Datasheet, PDF (189/441 Pages) Motorola, Inc – Integrated Processor with DMA User’s Manual | |||
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Freescale Semiconductor, Inc.
attempting to read the stack frame. The version number is located in the most significant
byte (bits 15â8) of the internal register word at location SP + $14 in the stack frame. The
validity check ensures that stack frame data will be properly interpreted in multiprocessor
systems.
If a frame is invalid, a format error exception is taken. If it is inaccessible, a bus error
exception is taken. Otherwise, the processor reads the entire frame into the proper
internal registers, de-allocates the stack (12 words), and resumes normal processing. Bus
error frames for faults during exception processing require the RTE instruction to rewrite
the faulted stack frame. If an error occurs during any of the bus cycles required by rewrite,
the processor halts.
If a format error occurs during RTE execution, the processor creates a normal four-word
fault stack frame below the frame that it was attempting to use. If a bus error occurs, a
bus-error stack frame will be created. The faulty stack frame remains intact, so that it may
be examined and repaired by an exception handler or used by a different type of
processor (e.g., MC68010, MC68020, or future M68000 processor) in a multiprocessor
system.
5.5.3 Fault Recovery
There are four phases of recovery from a fault: recognizing the fault, saving the processor
state, repairing the fault (if possible), and restoring the processor state. Saving and
restoring the processor state are described in the following paragraphs.
The stack contents are identified by the special status word (SSW). In addition to
identifying the fault type represented by the stack frame, the SSW contains the internal
processor state corresponding to the fault.
15
14
13
12
11
10
9
8
7
6
5
TP MV
0
TR
B1
B0 RR RM IN RW LG
TPâBERR frame type
MVâMOVEM in progress
TRâTrace pending
B1âBreakpoint channel 1 pending
B0âBreakpoint channel 0 pending
RRâRerun write cycle after RTE
RMâFaulted cycle was read-modify-write
INâInstruction/other
RWâRead/write of faulted bus cycle
LGâOriginal operand size was long word
SIZâRemaining size of faulted bus cycle
FUNCâFunction code of faulted bus cycle
4
3
SIZ
2
1
0
FUNC
5-52
MC68340 USERâS MANUAL
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