Arm Limited

Daniel Luke Kefford

David Hennah Mansell

Daniel Kershaw

James Ian McNiven

A data processing apparatus and method are provided for controlling access to registers. The data processing apparatus comprises a processing unit for performing data processing operations on data values, the processing unit having a plurality of modes of operation. A plurality of registers are provided for storing data values for access by the processing unit, with a subset of those registers being mode specific registers. Each mode specific register is used by the processing unit when operating in an associated mode of operation. The processing unit is switchable between a plurality of contexts, the data values stored in the plurality of registers being dependent on a current context of the processing unit. The processing unit performs a switch operation to switch from the current context to a new context, during which the data values in the registers are updated having regard to the new context. A control register is provided which, for at least one mode of operation having at least one mode specific register associated therewith, has an access field which is programmable by the processing unit when operating in a predetermined mode of operation. When the access field is set, the processing unit is selectively denied access to the associated at least one mode specific register, whereby updating of the data values in the associated at least one mode specific register is avoided during the switch operation. This significantly increases the speed of the switch operation.

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London, United Kingdom

Daniel Luke Kefford