Patent ID: 7529916
Filing Date: 2009-05-05
Classification: G06F

Abstract:
1. A data processing apparatus comprising: 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 for storing data values for access by the processing unit when performing said data processing operations, a subset of said registers being mode specific registers, each mode specific register being for use by the processing unit when operating in an associated mode of operation; the processing unit further being switchable between a plurality of contexts, the data values stored in said plurality of registers being dependent on a current context of the processing unit, the processing unit being operable to perform a switch operation to switch from the current context to a new context during which the data values in said plurality of registers are updated having regard to the new context; wherein the data processing apparatus includes a plurality of domains in which devices of the data processing apparatus operate, said plurality of domains comprising a secure domain and a non-secure domain, where in the secure domain the processing unit has access to secure data not accessible in the non-secure domain, and each of said plurality of contexts is associated with one of those domains a control register 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 being denied access to said associated at least one mode specific register if the current context is at least one predetermined context associated with the non-secure domain, whereby updating of the data values in said associated at least one mode specific register is avoided during said switch operation if either the current context or the new context is said at least one predetermined context.