Abstract: Signature generation circuitry is configured to update a signature in response to each of a plurality of writes to memory. The signature is updated by performing bitwise operations between current bit values of the signature and at least some of the bits written to memory in response a write. The bitwise operation are order-independent such that the resulting signature is the same irrespective of the order in which the writes are used to update the signature. The signatures are formed in an order-independent manner such that, if no errors have occurred in generating the data to be written to be memory, the signatures will match. In this way, a compact signature is developed that is suitable export from the data processing device for checking against a corresponding data processing device of a machine running a duplicate application.

Abstract: During normal operation of a processor, voltage droop is likely to occur and there is, therefore, a need for techniques for rapidly and accurately detecting this droop so as to reduce the probability of circuit timing failures. The droop detector described herein uses a tap sampled delay line in which a clock signal is split along two separate paths. Each of the taps in the paths are separated by two inverter delays such that the set of samples produced represent sample values of the clock signal that are each separated by a single inverter delay without inversion of the first clock signal between the samples.

Abstract: Signature generation circuitry is configured to update a signature in response to each of a plurality of writes to memory. The signature is updated by performing bitwise operations between current bit values of the signature and at least some of the bits written to memory in response a write. The bitwise operation are order-independent such that the resulting signature is the same irrespective of the order in which the writes are used to update the signature. The signatures are formed in an order-independent manner such that, if no errors have occurred in generating the data to be written to be memory, the signatures will match. In this way, a compact signature is developed that is suitable export from the data processing device for checking against a corresponding data processing device of a machine running a duplicate application.

Abstract: A memory controller is provided for reading and writing to and from a memory module. The memory controller implements an error correction algorithm, which calculates error correction code for message data to be written to the memory module and checks the error correction code against the message data when the data is read out of the memory module. The memory controller spreads each codeword over at least four different beats sent over the interface with the memory module, with each beat comprising a symbol of error correction code. Bits of a particular symbol of message data occupy the same positions in different beats. Since the bits of the symbols occupy the same positions in different beat, the number of bits affected by a hardware error is minimised. With four symbols of error correction code available for use in the codeword.

Abstract: A hardware module comprising circuitry configured to: store a sequence of n bits in a register of the hardware module; generate a signed integer comprising a magnitude component and a sign bit by: if the most significant bit of the sequence of n bits is equal to one: set each of the n?1 of the most significant bits of the magnitude component to be equal to the corresponding bit of the n?1 least significant bits of the sequence of n bits; and set the sign bit to be zero; if the most significant bit of the sequence of n bits is equal to zero: set each of the n?1 of the most significant bits of the magnitude component to be equal to the inverse of the corresponding bit of the n?1 least significant bits of the sequence of n bits; and set the sign bit to be one.

Abstract: During normal operation of a processor, voltage droop is likely to occur and there is, therefore, a need for techniques for rapidly addressing this droop so as to reduce the probability of circuit timing failures. This problem is addressed by provided an apparatus that is configured to detect the droop and react to mitigate the droop. The apparatus includes a frequency divider that is configured to receive an output of a clock signal generator (e.g. a phase locked loop) and produce an output signal in which a predefined fraction of the clock pulses in the output of the clock signal generator are removed from the output signal. By reducing the frequency of the clock signal in this way (as may be understood by examining equation 3) VDD is increased, hence mitigating the voltage droop. This technique provides a fast throttling mechanism that prevents excessive VDD droop across the processor.

Abstract: During normal operation of a processor, voltage droop is likely to occur and there is, therefore, a need for techniques for rapidly and accurately detecting this droop so as to reduce the probability of circuit timing failures. The droop detector described herein uses a tap sampled delay line in which a clock signal is split along two separate paths. Each of the taps in the paths are separated by two inverter delays such that the set of samples produced represent sample values of the clock signal that are each separated by a single inverter delay without inversion of the first clock signal between the samples.

Abstract: A computer program comprising a sequence of instructions for execution on a processing unit having instruction storage for holding the computer program, an execution unit for executing the computer program and data storage for holding data, the computer program comprising: a switch control instruction which when executed causes the processing unit to control switching circuitry to connect a set of connection wires of the processing unit to a switching fabric to receive a data packet at a predetermined received time, the switch control instruction comprising a delay control field which holds a value defining a delay between issuance of the instruction in the sequence of instructions and its execution by the execution unit.

Abstract: The invention relates to a computer program comprising a sequence of instructions for execution on a processing unit having instruction storage for holding the computer program, an execution unit for executing the computer program and data storage for holding data, the computer program comprising one or more computer executable instruction which, when executed, implements: a send function which causes a data packet destined for a recipient processing unit to be transmitted on a set of connection wires connected to the processing unit, the data packet having no destination identifier but being transmitted at a predetermined transmit time; and a switch control function which causes the processing unit to control switching circuitry to connect a set of connection wires of the processing unit to a switching fabric to receive a data packet at a predetermined receive time.

Abstract: An execution unit for a processor, the execution unit comprising: a look up table having a plurality of entries, each of the plurality of entries comprising an initial estimate for a result of an operation; a preparatory circuit configured to search the look up table using an index value dependent upon the operand to locate an entry comprising a first initial estimate for a result of the operation; a plurality of processing circuits comprising at least one multiplier circuit; and control circuitry configured to provide the first initial estimate to the at least one multiplier circuit of the plurality of processing circuits so as perform processing, by the plurality of processing units, of the first initial estimate to generate the function result, said processing comprising applying one or more Newton Raphson iterations to the first initial estimate.

Abstract: A function approximation system is disclosed for determining output floating point values of functions calculated using floating point numbers. Complex functions have different shapes in different subsets of their input domain, making them difficult to predict for different values of the input variable. The function approximation system comprises an execution unit configured to determine corresponding values of a given function given a floating point input to the function; a plurality of look up tables for each function type; a correction table of values which determines if corrections to the output value are required; and a table selector for finding an appropriate table for a given function.

Abstract: Two or more die are stacked together in a stacked integrated circuit device. Each of the processors on these die is able to communicate with other processors on its die by sending data over the switching fabric of its respective die. The mechanism for sending data between processors on the same die (i.e. intradie communication) is reused for sending data between processors on different die (i.e. interdie communication). The reuse of the mechanism is enabled by assigning each processor a vertical neighbour on its opposing die. Each processor has an interdie connection that connects it to the output exchange bus of its neighbour. A processor is able to borrow the output exchange bus of its neighbour by sending data along the output exchange bus of its neighbour.

Abstract: A time deterministic computer is architected so that exchange code compiled for one set of tiles, e.g., a column, can be reused on other sets. The computer comprises: a plurality of processing units each having an input interface with a set of input wires, and an output interface with a set of output wires: a switching fabric connected to each of the processing units by the respective set of output wires and connectable to each of the processing units by the respective set of output wires and connectable to each of the processing units by the respective input wires via switching circuitry controllable by its associated processing unit; the processing units arranged in columns, each column having a base processing unit proximate the switching fabric and multiple processing units one adjacent the other in respective positions in the direction of the column.

Abstract: An execution unit for a processor, the execution unit comprising: a look up table having a plurality of entries, each of the plurality of entries comprising an initial estimate for a result of an operation; a preparatory circuit configured to search the look up table using an index value dependent upon the operand to locate an entry comprising a first initial estimate for a result of the operation; a plurality of processing circuits comprising at least one multiplier circuit; and control circuitry configured to provide the first initial estimate to the at least one multiplier circuit of the plurality of processing circuits so as perform processing, by the plurality of processing units, of the first initial estimate to generate the function result, said processing comprising applying one or more Newton Raphson iterations to the first initial estimate.

Abstract: A memory controller is provided for reading and writing to and from a memory module. The memory controller implements an error correction algorithm, which calculates error correction code for message data to be written to the memory module and checks the error correction code against the message data when the data is read out of the memory module. The memory controller spreads each codeword over at least four different beats sent over the interface with the memory module, with each beat comprising a symbol of error correction code. Bits of a particular symbol of message data occupy the same positions in different beats. Since the bits of the symbols occupy the same positions in different beat, the number of bits affected by a hardware error is minimised. With four symbols of error correction code available for use in the codeword.

Abstract: An execution unit configured to execute a computer program instruction to generate random numbers based on a predetermined probability distribution. The execution unit comprises a hardware pseudorandom number generator configured to generate at least randomised bit string on execution of the instruction and adding circuitry which is configured to receive a number of bit sequences of a predetermined bit length selected from the randomised bit string and to sum them to produce a result.

Abstract: A function approximation system is disclosed for determining output floating point values of functions calculated using floating point numbers. Complex functions have different shapes in different subsets of their input domain, making them difficult to predict for different values of the input variable. The function approximation system comprises an execution unit configured to determine corresponding values of a given function given a floating point input to the function; a plurality of look up tables for each function type; a correction table of values which determines if corrections to the output value are required; and a table selector for finding an appropriate table for a given function.

Abstract: The invention relates to a computer program comprising a sequence of instructions for execution on a processing unit having instruction storage for holding the computer program, an execution unit for executing the computer program and data storage for holding data, the computer program comprising one or more computer executable instruction which, when executed, implements: a send function which causes a data packet destined for a recipient processing unit to be transmitted on a set of connection wires connected to the processing unit, the data packet having no destination identifier but being transmitted at a predetermined transmit time; and a switch control function which causes the processing unit to control switching circuitry to connect a set of connection wires of the processing unit to a switching fabric to receive a data packet at a predetermined receive time.

Abstract: A pseudo random number generator implemented in hardware. The pseudo random number generator comprises a state post processing circuit for processing two state values to produce a random number. The circuit having a first combinatorial logic comprising a XOR or XNOR gate configured to process a first pair of bits from the state values, a second combinatorial logic comprising an OR or AND gate configured to process a second pair of bits from the state value, and third combinatorial logic comprising an OR or AND gate configured or process a third pair of bits from the state value. The circuit has fourth combinatorial logic configured to process the outputs of the first three set of combinatorial logic so as to provide a result bit of the random number. The fourth combinatorial logic comprises an AND or OR gate and a XOR or XNOR gate.

Abstract: A time deterministic computer is architected so that exchange code compiled for one set of tiles, e.g., a column, can be reused on other sets.