Hewlett-packard Company

Agilent Technologies, Inc.

Craig A Heikes

Robert H Miller, Jr

David R Smentek

Glenn T Colon-Bonet

Russell W Mason

Rodolfo G Beraha

A communications socket between a logic simulator and a system for generating input stimuli based on the current state of the logic simulator is provided. Input stimuli to the logic simulator for use in implementing a particular circuit design simulation are calculated by interfacing an input program which models the function of the circuit being designed with the logic simulator. The lines in this input program are converted by an adaptive vector generator into communications signals which are understandable by the logic simulator so that the desired simulation may take place. The input program thus enables the adaptive vector generator to behaviorally model complex logical systems that the logic simulator model is only a part of and allows for more accurate and detailed simulation. The adaptive vector generator does this by determining the next input vector state in accordance with the present state of the logic simulator model as received from the communications socket. In other words, based on the state data received from the logic simulator, the adaptive vector generation automatically calculates the next stimulus pattern for the logic simulator model and provides this stimuli to the logic simulator through the communications socket. This technique removes the tediousness of the prior art techniques in that the design engineer no longer needs to specify every input step and to anticipate the output state of the circuit.

Bidirectional socket stimulus interface for a logic simulator

The present invention provides a system and method for performing precharge timing verification on a logic circuit comprising a plurality of cascaded logic blocks, where in each logic block is implemented via a dynamic logic gate characterized by having a clock resettable output. In addition, a storage element is connected at each input to the logic circuit. The method of the present invention includes the following steps: preconditioning the storage elements so that all the inputs to the logic circuit are driven high when the clock goes high; transitioning the clock high so as to drive all the inputs of the logic circuit high, thereby driving all the outputs of the logic circuit high and discharging the storage node of each logic block; transitioning the clock low to precharge the storage node of all the logic blocks in the logic circuit, and thereby driving all the outputs low; and determining the longest precharge path in the logic circuit. A precharged timing verification system of the present invention is preferably implemented on a computer system and comprises a dynamic simulation mechanism and a precharge timing mechanism for performing the precharge timing verification timing analysis of the present invention.

System and method for verification of a precharge critical path for a

An apparatus and method are disclosed for regulating power consumption in a digital system of the kind including at least one triggerable functional block that consumes more power when triggered than when not triggered. In an embodiment for use with a digital system that includes a pipeline of such triggerable functional blocks, a state machine sequentially applies trigger pulses to each of the functional blocks in the pipeline whenever the output of an OR gate is asserted. It does so by generating a series of enable signals that are used to gate a clock signal to the trigger inputs of the functional blocks. The state machine includes a series of storage devices having outputs. Outputs of the storage devices are used to provide the enable signals. The inputs of the OR gate are coupled to a start signal that indicates when the functional blocks should be triggered to process data, and also to a dummy start signal that indicates when the functional blocks should be triggered to maintain power consumption. Outputs from the storage devices are also used to indicate the number of times the pipeline has been triggered during a recent number of clock cycles. A programmable register is used to store a data value corresponding to the minimum desired level of power consumption for the pipelined functional blocks. The dummy start signal is generated by combinational logic whose inputs include the outputs of the storage devices and the data value. Because the minimum desired level of power consumption may be programmed by the user, thermal characterization and balancing of step load with average power are facilitated.

Apparatus and method for regulating power consumption in a digital system

The operation of a pipeline is observed by launching two or more sets of data into the pipeline on consecutive clock cycles. The clock free-runs for as many cycles as it takes the data to propagate through the stages of the pipeline. The output latches of each stage of the pipeline are only sampled when the data of interest is held in each output latch, respectively. Observation may be completely controlled through a standard test access port (TAP). Observation may be accomplished by halting the clock to scan new data in and results out, or with the clock free-running. The inputs to the pipeline may come from test registers or from circuitry which feeds the pipeline during normal operation.

Method and apparatus for at speed observability of pipelined circuits

A system and method for quiescent current testing of dynamic logic circuitry. Nodes shorted to ground are detected during a dynamic pre-charge state. Nodes shorted to a power supply potential are detected by driving all nodes of interest to ground during a dynamic evaluation phase. Nodes of interest are driven to ground directly by one additional transistor per node or indirectly by logical propagation from upstream nodes. As a result, only two current measurements are needed for all shorted node faults, even for pipelined systems with multiple clocks. There is no need for input test signal sequences and no need for signal propagation to outputs for detection. Specific embodiments are provided for single-rail logic, single-rail pipelined systems, dual-rail logic and dual-rail pipelined systems. For single-rail pipelined systems, optional transistors between stages enable preservation of logical states during testing. For dual-rail logic, storage nodes and static nodes are forced to a logical state that is not possible during normal operation. For pipelined dual-rail logic, testing of alternate stages inherently preserves the logical state of the system during testing.

Quiescent current testing of dynamic logic systems

A rounding means is associated with a carry propagate adder of a floating point processor in order to reduce latency and enhance performance. The rounding mechanism performs a rounding function approximately simultaneously with an addition function performed by the carry propagate adder on fraction inputs FA, FB to ultimately derive a resultant fraction FR, thereby eliminating the need for a conventional post-normalize incrementer. The rounding mechanism has a carry select adder and rounding logic network. The rounding logic network communicates with the carry propagate adder and the carry select adder in order to provide rounding information to the carry select adder. The carry select adder and the rounding logic network jointly provide a rounded output, which is then normalized by the normalizer to thereby derive the resultant fraction.

System and method for reducing latency in a floating point processor

The present invention tolerates the decay of a dynamic logic circuit by preserving the logic state of the output before the decay. A slow clock detector is configured to detect a slow clock condition of the clock pertaining to the dynamic logic circuit. A tolerant storage device is configured to preserve the data output by command of the slow clock detector upon a detection of the slow clock condition.

System and method for tolerating dynamic circuit decay

A circuit and a method for providing an indication of the position of a bit having a selected characteristic in an n-bit binary word are disclosed. The n bits of the binary word are arranged into groups of W bits so that each group is input to a fundamental encoder. The position of the bit having the selected characteristic, among each group of W bits is provided as an encoded output. A multiplexer tree provides a single output indicative of the position of the bit having the selected characteristic in the binary word based on the encoded outputs from the encoders.

Minimal delay leading one detector with result bias control

A technique for encoding multiple floating point formats into a double precision floating point number by padding single word floating point numbers with zeros to form a 64-bit double word in a way that allows a single precision arithmetic logic unit to be built on top of a double precision arithmetic logic unit. The formatting circuitry of the invention requires only small differences in the hardware for single and double precision operations so as to simplify the arithmetic logic unit and the multiplier of the floating point processing units. The encoding technique of the invention includes right justifying the exponent and mantissa of the floating point number in a 'common format' such that rounding of the mantissa need only occur in one place, thereby greatly simplifying the rounding procedure. The technique of the invention also removes multiplexers from critical speed paths in the floating point processing units when it is desired to accommodate multiple data formats.

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Fort Collins, CO, United States of America

Craig A Heikes