Embedded Systems Design, 2nd Edition

206 Embedded systems design

from the beginning. If the exception occurred in the middle of the

instruction, the restart repeats the initial action. For many instruc-

tions this may not be a problem — but it can lead to some

interesting situations concerning memory and I/O accesses.

If the instruction is accessing multiple memory locations

and fails after the second access, the first access will be repeated.

The store multiple type of instruction is a good example of this,

where the contents of several registers are written out to memory.

If the target address is an I/O peripheral, an unexpected repeat

access may confuse it.

While the majority of the M68000 ...