MC68340 datasheet(189/441 Pages) FREESCALE

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MC68340 USER’S MANUAL

MOTOROLA

attempting to read the stack frame. The version number is located in the most significant

byte (bits 15–8) 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.

9876543210

SIZ

FUNC

TP—BERR frame type

MV—MOVEM in progress

TR—Trace pending

B1—Breakpoint channel 1 pending

B0—Breakpoint channel 0 pending

RR—Rerun write cycle after RTE

RM—Faulted cycle was read-modify-write

IN—Instruction/other

RW—Read/write of faulted bus cycle

LG—Original operand size was long word

SIZ—Remaining size of faulted bus cycle

FUNC—Function code of faulted bus cycle

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