Automatic source synchronous bus signal alignment compensation mechanism

An apparatus that compensates for misalignment on a synchronous data bus, the apparatus comprising:

• a microprocessor, comprising:
• a Joint Test Action Group (JTAG) interface, configured to receive control information over a standard JTAG bus, wherein said control information indicates an amount to adjust a propagation time;
• and
• a bit lag control element, configured to measure said propagation time beginning with assertion of a first signal and ending with assertion of a second signal, and configured to generate a first value on a lag bus that indicates an adjusted propagation time, said bit lag control element comprising:
• delay lock control, configured to select one of a plurality of successively delayed versions of said first signal that coincides with said assertion said second signal, and configured to generate a second value on a lag select bus that indicates said propagation time;
• adjust logic, coupled to said JTAG interface and to said lag select bus, configured adjust said second value by said amount prescribed by said JTAG interface to yield a third value that is output to an adjusted lag bus;
• and
• a gray encoder, configured to gray encode said third value to generate said first value on said lag bus.

A method that compensates for misalignment on a synchronous data bus, the method comprising:

• receiving control information over a standard JTAG bus, wherein the control information indicates an amount to adjust a propagation time;
• and
• measuring the propagation time beginning with assertion of a first signal and ending with assertion of a second signal, said measuring comprising:
• selecting one of a plurality of successively delayed versions of the first signal that coincides with assertion of the second signal;
• adjusting the propagation time by the amount prescribed by the control information to yield an adjusted propagation time;
• and
• gray encoding the adjusted propagation time to generate a value on a lag bus.