Abstract: A processor comprises an exchange, a plurality of columns, and a plurality of exchange scan chains. The exchange comprises a plurality of exchange paths, each comprising a set of exchange path portions, for transmitting data between processing units. Each of the plurality of column comprises processing units, each processing unit connected to output data to a respective exchange path, and column pipe circuitry for providing a controllable path between the exchange and the processing units. The column pipe circuitry comprises a column wrapper chain for preventing a scan test signal from passing between the exchange paths and the processing units. The exchange scan chains enable scan testing of the exchange paths. Each exchange scan chain comprises a plurality of scan chain segments, each scan chain segment comprises an exchange path portion connected to at least one of the processing units of at least one of the columns of the processor.

Abstract: A processor comprising at least one processing module, each processing module comprising: an execution pipeline; memory; an instruction fetch unit comprising operable to switch between an operational mode and a debugging mode, the instruction fetch unit being configured so as, when in the operational mode, to fetch machine code instructions from the memory into the execution pipeline to be executed; and a debug interface for connecting to a debug adapter. The debug interface comprises a debug instruction register enabling the debug adapter to write a machine code instruction to the debug instruction register, and wherein the instruction fetch unit is configured so as, when in the debug mode, to fetch instructions from the debug instruction register into the pipeline instead of from the memory.

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: A method of allocating variables to computer memory includes determining at compile time when each of the plurality of variables is live in a memory region and allocating a memory region to each variable wherein at least some variables are allocated at compile time to overlapping memory regions to be stored in those memory regions at runtime at non-overlapping times.

Abstract: According to an aspect of the invention, there is provided a computer comprising a plurality of interconnected processing nodes arranged in a configuration with multiple stacked layers. Each layer comprises four processing nodes connected by respective links between the processing nodes. In end layers of the stack, the four processing nodes are interconnected in a ring formation by two links between the nodes, the two links adapted to operate simultaneously. Processing nodes in the multiple stacked layers provide four faces, each face comprising multiple layers, each layer comprising a pair of processing nodes. The processing nodes are programmed to operate a configuration to transmit data around embedded one-dimensional rings, each ring formed by processing nodes in two opposing faces.

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 method for controlling the sending of data by a plurality of processors belonging to a device, the method comprising: sending a first message to a first processor of the plurality of processors to grant permission to the first processor of the plurality of processors to send a first set of data packets over at least one external interface of the device; receiving from the first processor, an identifier of a second processor of the plurality of processors; and in response to receipt of the identifier of the second processor, send a second message to the second processor to grant permission to the second processor to send a second set of data packets over the at least one external interface.

Abstract: A method for generating an executable program to run on one or more processor modules. The method comprises: receiving a graph comprising a plurality of data nodes, compute vertices and edges; and compiling the graph into an executable program including one or more types of multi-access instruction each of which performs at least two memory access (load and/or store) operations in a single instruction. The memory on each processor module comprises multiple memory banks whereby the same bank cannot be accessed by different load or store operations in the same instruction. The compilation comprises assigning instances of the multi-access instructions to implement at least some of the graph edges, and allocating the data to memory addresses within different ones of the banks. The allocating is performed subject to one or more constraints, including at least that different load/store operations should not access the same memory bank in the same instruction.

Abstract: A computer comprising a plurality of interconnected processing nodes arranged in multiple stacked layers forming a multi-face prism is provided. Each face of the prism comprises multiple stacked pairs of nodes. Said nodes are connected by at least two intralayer links. Each node is connected to a corresponding node in an adjacent pair by an interlayer link. The corresponding nodes are connected by respective interlayer links to form respective edges. Each pair forms part of a layers, each layer comprising multiple nodes, each node connected to their neighbouring nodes in the layer by at least one of the intralayer links to form a ring. Data is transmitted around paths formed by respective sets of nodes and links, each path having a first portion between a first and second endmost layers, and a second portion provided between the second and first endmost layers and comprising one of the edges.

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 network comprising interconnected first and second processors, each processor comprising one or more of: multiple processing units arranged on a chip configured to execute program code; an on-chip interconnect comprising groups of exchange paths connected to receive data from corresponding groups of the processing units; external interfaces configured to communicate data off-chip as packets, each having a destination address, external interfaces of the first and second processors being connected by an external link; multiple exchange blocks, each connected to groups of the exchange paths; a routing bus configured to route packets between the exchange blocks and the external interfaces. Processing units of the first processor generate off-chip packets such that the group of processing units serviced by the first exchange block on the first processor address off-chip packets to the group of processing units on the second processor serviced by the corresponding first exchange block of the second processor.

Abstract: A method of recording tile identifiers in each of a plurality of tiles of a multitile processor is described. Tiles are arranged in columns, each column having a plurality of processing circuits, each processing circuit comprising one or more tiles, wherein a base processing circuit in each column is connected to a set of processing circuit identifier wires. A base value is generated on each of the set of processing circuit identifier wires for the base processing circuit in each column. At the base processing circuit, the base value on the set of processing circuit identifier wires is read and incremented by one. The incremented value is propagated to a next processing circuit in the column, and at the next processing circuit a unique identifier is recorded by concatenating an identifier of the column and the incremented value.

Abstract: A hardware module comprises at least a first ingress buffer and a second ingress buffer, where the second ingress buffer holds data packets from a plurality of source components. To ensure fairness between one or more sources providing data to the first ingress buffer and the plurality of sources providing data to the second ingress buffer, processing circuitry examines source identifiers in packets held in the second ingress buffer and selects between the buffers so as to arbitrate between the sources. In some embodiments, the examination of the source identifiers provides statistics for a weighted round robin between the ingress buffers. In other embodiments, the source identifier of whichever packet is currently at the head of the second ingress buffer is used to perform a simple round robin between the sources.

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 system comprising a gateway for interfacing external data sources with one or more accelerators. The gateway comprises a plurality of virtual gateways, each of which is configured to stream data from the external data sources to one or more associated accelerators. The plurality of virtual gateways are each configured to stream data from external data sources so that the data is received at an associated accelerator in response to a synchronisation point being obtained by a synchronisation zone. Each of the virtual gateways is assigned a virtual ID so that when data is received at the gateway, data can be delivered to the appropriate gateway.

Abstract: In a computer comprising multiple processing units, a method of exchanging read only elements between the processing units is described. The read only elements may be code or data, such as vector or matrix data for an AI graph. A master processing unit is identified. At compile time, at least one shareable read only element is allocated to the master processing unit. The at least one shareable read only element is stored in the local memory of the master processing unit. At compile time a transmitting exchange code sequence designated to be executed at the execution stage of the master processing unit is also allocated to the master processing unit. At a time point determined at compile time, the transmitting exchange code sequence causes the processing unit to identify the shareable read only element and to generate a message to be transmitted for reception by another processing unit, the message comprising the shareable read only data element.

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 data processing system for training a neural network, the data processing system comprising: a first set of one or more processing units running one model of the neural network, a second set of one or more processing units running another model of the neural network, a data storage, and an interconnect between the first set of one or more processing units, the second set of processing units and the data storage, wherein the data storage is configured to provide over the interconnect, training data to the first set of one or more processing units and the second set of one more processing units, wherein each of the first and second set of processing units is configured to, when performing the training, evaluate loss for the respective training iteration including a measure of the dissimilarity between the output values calculated based on the different modes running on the first and second set of processing units, wherein the dissimilarity measure is weighted in the evaluation of the loss in accordance with a

Abstract: A multitile processing system has an execution unit on each tile, and an interconnect which conducts communications between the tiles according to a bulk synchronous parallel scheme. Each tile performs an on-tile compute phase followed by an intertile exchange phase, where the exchange phase is held back until all tiles in a particular group have completed the compute phase. On completion of the compute phase, each tile generates a synchronisation request and pauses an issue of instructions until it receives a synchronisation acknowledgement. If a tile attains an excepted state, it raises an exception signal and pauses instruction issue until the excepted state has been resolved. However, tiles which are not in the excepted state can continue to perform their on-tile computer phase, and will issue their own synchronisation request in their own normal time frame.