Clock pulse measuring and deskewing system and process
AssigneeCray Research, Inc.
InventorsMark R. Sikkink, Kenneth A. Van Goor, Gregory R. Edlund, Arthur H. Orth
Life of this patent
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Abstract
The skew of a circuit within a clock pulse distributing network is determined by establishing a closed loop circuit including the circuit under test. A sampling period is established such as by a counter actuated by the clock pulses. During that sampling period, the number of pulses recurring within the closed loop circuit are counted in yet another counter. The count is then useful not only to indicate the magnitude of the circuit skew but also allows optimization of the delay introduced to the circuit under test during normal operation. The skew is thus determined dynamically under typical machine environment situations.
Claims23
Apparatus for determining the delay of a pulse delivering circuit for delivering clock pulses from a source to a device which utilizes the clock pulses comprising
- means selectively operable for establishing a closed loop circuit including the pulse delivering circuit;
- means for introducing at least one pulse into said established closed loop circuit such that said introduced pulse recirculates through said closed loop circuit;
- and
- means for determining the length of time for said introduced pulse to recirculate through said closed loop circuit.
Apparatus for periodically adjusting the amount of delay applied to system clock pulses by a pulse transferring circuit connecting the clock pulses from a source of clock pulses to a utilization device comprising
- variable delay means responsive to digital data for producing an output pulse subsequent to receipt of an input pulse with the delay therebetween corresponding to said digital data;
- means selectively operable for coupling said variable delay means between the source of the system clock pulses and the pulse transferring circuit;
- means selectively operable for deactivating said coupling means for decoupling said variable delay from the source of clock pulses and for establishing a closed loop ringing circuit including said variable delay means and said pulse transferring circuit;
- means for introducing a pulse from said source into said closed loop ringing circuit such that said introduced pulse rings through said closed loop ringing circuit;
- and
- means for determining the number of times said introduced pulse rings within said closed loop ringing circuit over a predetermined sampling time period.
The method of determining the delay of a pulse delivering circuit for delivering clock pulses from a source to a clock pulse utilizing device comprising the steps of
- establishing a closed loop circuit including the clock pulse delivering circuit in isolation from the clock pulses;
- introducing a clock pulse from the source into said closed loop circuit such that said introduced clock pulse rings through said closed loop circuit;
- and
- determining the length of time for said ringing pulse to recirculate through said closed loop circuit.
The method of determining the delay of each of a plurality of circuit networks wherein said networks deliver clock pulses from a common source to a respective one of a plurality of clock pulse utilizing devices through a delay circuit capable of producing a signal at the output thereof delayed relative to the time of arrival of the signal at the input thereof by an amount corresponding to the magnitude of a control signal introduced thereto comprising the steps of
- establishing a closed loop ringing circuit including the clock pulse delivering network in isolation from the clock pulses for each such network;
- introducing a pulse from said common source into each of said closed loop ringing circuits such that said introduced pulse rings through each of said closed loop ringing circuits;
- determining the number of ringing pulses to recirculate within said closed loop circuit of each network over a predetermined period of time.
Dependencies are inferred from the claim text.