Source synchronous bus signal alignment compensation mechanism

Abstract

An apparatus having a bit lag control element that measures a propagation time beginning with assertion of a first signal and ending with assertion of a second signal, and that generates a first value indicating an adjusted propagation time. The control element includes delay lock control, adjust logic, and a gray encoder. The delay lock control selects one of a plurality of successively delayed versions of the first signal that coincides with the assertion the second signal, and generates a second value on a lag select bus that indicates the propagation time. The adjust logic is coupled to a circuit and to the lag select bus, and adjusts the second value by an amount prescribed by the circuit to yield a third value that is output to an adjusted lag bus. The gray encoder gray encodes the third value to generate the first value on the lag bus.