An SMP computer system has an apparatus and method for recalibrating a self-timed,
source-synchronous, pipelined interface while the computer system is running. The
apparatus allows for quiescing the interface (ie. idling the processors to allow
for no data transfers), raising fences (blocking interfaces), allowing for a quick
clock centering recalibration step, and then unfencing and unquiescing to allow
for the use of the interface again. The recalibration allows for compensating for
drift over time on the interface to compensate for temperature, voltage, cycle
time, and end-of-life degradation without bringing down and restarting the system.
