Arm Limited

Richard York

Dominic Hugo Symes

Stuart David Biles

Simon John Craske

Andrew Christopher Rose

David James Seal

Antony John Penton

Alex James Waugh

Simon Andrew Ford

Paul Stanley Hughes

Hedley James Frances

A data processing apparatus is provided comprising processing circuitry for performing data processing operations, a set associative storage device for storing data values for access by the processing circuitry when performing data processing operations, error detection circuitry for performing, for each access to the storage device, an error detection operation on the data value accessed, and maintenance circuitry associated with the storage device for performing one or more maintenance operations. The processing circuitry is arranged to issue an error detection maintenance request to the maintenance circuitry specifying at least one specific physical location within the storage device, and the maintenance circuitry is responsive to the error detection maintenance request to perform at least one dummy access to the at least one specific physical location within the storage device and to provide the processing circuitry with error status information derived from the error detection operation performed by the error detection circuitry in respect of said at least one dummy access.

Error correction in a set associative storage device

A digital signal processing system comprising a central processing unit core 2, a memory 8 and a coprocessor 4 operates using coprocessor memory access instructions (e.g. LDC, STC). The addressing mode information within these coprocessor memory access instructions (P, U, W, Offset) not only controls the addressing mode used by the central processing unit core 2 but is also used by the coprocessor 4 to determine the number of data words in the transfer being specified such that the coprocessor 4 can terminate the transfer at the appropriate time. Knowledge in advance of the number of words in a transfer is also advantageous in some bus systems, such as those that can be used with synchronous DRAM. The Offset field within the instruction may be used to specify changes to be made in the value provided by the central processing unit core 2 upon execution of a particular instruction and also to specify the number of words in the transfer. This arrangement is well suited to working through a regular array of data such as in digital signal processing operations. If the Offset field is not being used, then the number of words to be transferred may default to 1.

Coprocessor data access control

The present invention provides a data processing apparatus comprising: a plurality of registers for storing data items to be processed; a processor for processing instructions to be applied to data items stored in said plurality of registers; and register remapping logic for converting a logical register reference within a preselected set of instructions to a physical register reference identifying the register containing the data item required for processing by the processor. By this approach, a remapping instruction need only be executed once in order for the remapping to be applied to a desired number of instructions. This is in contrast to prior art techniques, where subsequent to a remapping instruction being executed, the remapping is applied to all subsequent instructions, ie. a desired number of instructions cannot be selected. The invention is particularly advantageously employed in apparatus arranged to repeat an instruction loop, the instruction loop including said preselected set of instructions. In such cases, loop hardware used to manage the repeat instruction can be arranged to update the register remapping logic each time the instruction loop is repeated, and hence the remapping instruction used to configure the register remapping logic is only executed once prior to the repeat instruction being executed.

Non-instruction base register addressing in a data processing apparatus

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Cambridge, United Kingdom

Richard York