Trainable link

A method is provided to align clock and data signals over a source-synchronous link. The method includes sending header data and a default clock signal over the link. The header indicates a start of a training packet and the default clock signal ensures that the header is received without error. The method further includes providing a long clock pulse, phase shifting the clock signal during the long clock pulse, and thereafter sending training data and the clock signal over the link. The above steps are repeated until the training data are received with error. At that point, the phase shift of the clock signal is saved as a boundary of an optimal alignment. The above steps are then repeated with the clock signal shifted in a different direction. Once another boundary is located, the boundary midpoint is saved as the phase shift that provides the optimal alignment.