A
processor lockstep is a technique used to achieve high reliability in a
microprocessor system. This is done by adding a second identical processor to a
system that monitors and verifies the operation of the system processor.
* The two processors are initialized to the same state during system
start-up, and they receive the same inputs (code, bus operations and
asynchronous events), so during normal operation the state of the two processors
is identical from clock to clock. They are said to be operating in lockstep. The
lockstep technique assumes that an error in either processor will cause a
difference between the states of the two processors, which will eventually be
manifested as a difference in the outputs, so the lockstep system monitors the
outputs of the two processors and flags an error in the case of a discrepancy.
[* Adapted from
IBM PowerPC Tips]
