Abstract: A multi-tile processing unit in which the tiles in the processing unit may be divided between two or more different external sync groups for performing barrier synchronisations. In this way, different sets of tiles of the same processing unit each sync with different sets of tiles external to that processing unit.

Abstract: A peripheral device, for use with a host, comprises one or more compute elements a security module and at least one encryption unit. The security module is configured to form a trusted execution environment on the peripheral device for processing sensitive data using sensitive code. The sensitive data and sensitive code are provided by a trusted computing entity which is in communication with the host computing device. The at least one encryption unit is configured to encrypt and decrypt data transferred between the trusted execution environment and the trusted computing entity via the host computing device. The security module is configured to compute and send an attestation to the trusted computing entity to attest that the sensitive code is in the trusted execution environment.

Abstract: A device comprising: a processing unit comprising at least one processor configured to: participate in barrier synchronisations, each of which separates a compute phase of the at least one processor from an exchange phase for the at least one processor; and exchange sync messages with a sync controller hardware unit so as to co-ordinate each of the barrier synchronisations; and sync trace circuitry configured to: receive one or more of the sync messages; and in response to each of the one or more of the sync messages, provide sync trace information for output from the device, the sync trace information comprising timing information associated with the respective sync message.

Abstract: A predictive clock controller is provided for modifying the frequency of a clock signal provided to a processing unit based on knowledge of the power usage by the application running on the processing unit during different execution periods. The predictive clock controller counts barrier syncs for the application, so as to determine where the application is in its sync schedule. The predictive clock controller is able to determine from the number of counted syncs, when the application will transition from one execution period to another execution period with different power requirements, and to adjust the clock frequency accordingly.

Abstract: A processing system comprising one or more chips, each comprising a plurality of tiles is described. Each tile comprises a respective processing unit and memory, the memory storing a codelet. The processing system has at least one encryption unit configured to encrypt and decrypt data transferred between the tiles and a trusted computing entity via an external computing device. The codelets are configured to instruct the tiles to transfer the encrypted data by reading from and writing to a plurality of memory regions at the external memory such that a plurality of streams of encrypted data are formed, each stream using an individual one of the memory regions at the external computing device.

Abstract: A system comprising: a first subsystem comprising at least one first processor, and a second subsystem comprising one or more second processors. A first program is arranged to run on the at least one first processor, the first program being configured to send data from the first subsystem to the second subsystem. A second program is arranged to run on the one more second processors, the second program being configured to operate on the data content from the first subsystem. The first program is configured to set a checkpoint at one or more points in time. At each checkpoint it records in memory of the first subsystem i) a program state of the second program, comprising a state of one or more registers on each of the second processors at the time of the checkpoint, and ii) a copy of the data content sent to the second subsystem since the respective checkpoint.

Abstract: Each of the processing devices stores an event vector, which is updated when certain events (e.g. memory errors, overtemperature events) occur on the device. Different elements of the vector correspond to different types of events. When an event of a given type occurs on one device, the update to the event vector on that device is propagated to other devices in the system. Those other devices, in response, update the corresponding element in their own event vector to indicate that an event of that given type has occurred in the system. In this way, events are aggregated between the different devices using the event vector. The event vector is considered to be a global event vector, since its elements indicate whether certain events have occurred across the entire system, and the vector is consistent across the system.

Abstract: Each of the nodes stores a number, referred to herein as a generation number, which is updated whenever the respective node undergoes a reset and restart from checkpoint. Since the nodes of the system participate in the same reset event, at most times, each generation number held by a node will be the same across the system. However, in some cases, when one node resets before another node, the generation numbers between those two nodes will differ. The data frames sent between the nodes each comprise a generation number of the sending node, which is checked by the recipient and only accepted if the generation number in the frames matches the generation number of the recipient node.

Abstract: A computer includes first and second computer devices of a first class. Each computer device of the first class includes first and second external ports, at least one memory controller to attach to external memory, and routing logic to route data from the first external port to one of the memory controller and the second external port. The computer further includes first and second computer devices of a second class. The first computer device of the second class is connected to the first external ports via respective first and second links. The second computer device of the second class is connected to the second external ports via respective third and fourth links. The first and second computer devices of the second class include processing circuitry to execute a computer program and are connected to the first and second links, or third and fourth links, respectively to transmit and receive messages.

Abstract: An error event vector is defined for the device, where each element of that error event vector is used to indicate whether or not an event of the associated event class has occurred for any of the components of the device. If so, a control node causes the respective element of each of the copies of the error event vector to be set to indicate that an error of the event class has occurred. A component, i.e. the second one of the components, performs a responsive action for the event class in response to the update to its own copy of the error event vector.

Abstract: A memory attachment and routing chip includes a single die having a set of external ports; at least one memory attachment interface comprising a memory controller to attach to external memory, and a fabric core in which routing logic is implemented. The routing logic can (i) receive a first packet of a first type from a first port of the set of ports, the first type of packet being a memory access packet with a memory address which lies in a range of memory addresses associated with the memory attachment and routing chip, detect the memory address and route the packet of the first type to the memory attachment interface. The routing logic can (ii) receive a second packet of a second type, the second type of packet being an inter-processor packet comprising a destination identifier identifying a processing chip external to the memory attachment.

Abstract: A gateway in a computing system for interfacing a host with a subsystem for acting as a work accelerator to the host, the gateway having: an accelerator interface for enabling the transfer of batches of data to the subsystem at pre-compiled data exchange synchronisation points attained by the subsystem; a data connection interface for receiving data to be processed from storage; and a gateway interface for connection to a third gateway. The gateway is configured to store a number of credits indicating at least one of: the availability of data for transfer to the subsystem at a pre-compiled data exchange synchronisation point; and the availability of storage for receiving data from the subsystem at a pre-compiled data exchange synchronisation point. The gateway uses these credits to control whether or not synchronisation barrier is passed by transmitting synchronisation requests upstream to the third gateway or simply acknowledging the requests received.

Abstract: A device comprising: a control bus; a plurality of requesting circuits each accessible on the control bus, wherein each of the plurality of requesting circuits is operable to dispatch read or write requests to the control bus for delivery to at least one of a plurality of receiving circuits, and the plurality of receiving circuits each accessible on the control bus, and each of which is operable to receive requests from the at least one control bus and service the requests by providing at least one of read or write access to storage associated with the respective receiving circuit, wherein the control bus provides a ring path configured to support, the requests in circulation in the ring path, wherein the control bus is configured to propagate each of at least some of the requests at least until those requests have been serviced by at least one of the receiving circuits.

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 device comprising: a bus forming a ring path for circulation of one or more data packets around the bus, wherein the one or more data packets comprises a trace report packet for collecting trace data from a plurality of components attached to the bus, wherein the bus is configured to repeatedly circulate the trace report packet with a fixed time period taken for each circulation of the ring path performed by the trace report packet; and the plurality of components, each of which comprises circuitry configured to, upon reception of the trace report packet at the respective component, insert one or more items of the trace data that have been obtained by the respective component.

Abstract: A method for securely terminating a distributed trusted execution environment (TEE) spanning a plurality of work accelerators. After wiping sensitive data from the memory of its accelerator, a root of trust for each accelerator is configured to receive confirmation that the data has been wiped from the processor memory in relevant other accelerators prior to moving on to the next stage at which the TEE on its associated accelerator is terminated. Since the data has been wiped from the other accelerators, even if a third party were to inject malicious code into the accelerator, they would be unable to read out the secret data from the other accelerators since the data has been wiped from those other accelerators. In this way, a mechanism is provided for ensuring that when the distributed TEE is terminated, malicious third parties are unable to read out confidential data from the accelerators.

Abstract: A method for securely terminating a distributed trusted execution environment spanning a plurality of work accelerators. Each accelerator is configured to self-isolate upon determining that the distributed TEE is to be terminated across the system of accelerators. The data is also wiped from the processor memory of each accelerator, such that the data cannot be read out from the processor memory once the accelerator's links are re-enabled. The self-isolation is performed on each accelerator prior to the step of terminating the TEE on that accelerator. An accelerator only re-enables its links to other accelerators once the data is wiped from its processor memory such that the secret data is removed from the accelerator memory.

Abstract: An apparatus is provided for converting the form in which a synchronisation request for a barrier synchronisation is provided. The synchronisation request is provided from a first synchronisation circuitry to a second synchronisation circuitry by asserting one of a set of separate signals that may each correspond to a bit in a register or a signal on a wire. The second synchronisation circuitry provides for the packetisation of the sync request by sending a packet comprising the sync request over a network to be received at a further subsystem.

Abstract: A processor in a network has a plurality of processing units arranged on a chip. An on-chip interconnect enables data to be exchanged between the processing units. A plurality of external interfaces are configured to communicate data off chip in the form of packets, each packet having a destination address identifying a destination of the packet. The external interfaces are connected to respective additional connected processors. A routing bus routes packets between the processing units and the external interfaces. A routing register defines a routing domain for the processor, the routing domain comprising one or more of the additional processor, and at least a subset of further additional processors of the network, wherein the additional processors of the subset are directly or indirectly connected to the processor. The routing domain can be modified by changing the contents of the routing register as a sliding window domain.

Abstract: The same test data frame is dispatched from a network interface device a plurality of times so as to test a network. Since the same test data frame is used, it may be unnecessary for a new test data frame to be provided and protocol processed each time one is required to be sent. The protocol processing resources of the network interface device are then available for sending further traffic in parallel with the dispatch of the test data frames. On the receive side, the network interface device collects statistics regarding the reliable receipt of test frames, without requiring the test frames to be further processed and provided to a driver of the network interface device. In this way, the processing and buffering capacity in the network interface device is available for handling further traffic in parallel with the test traffic.