Data processing system having multiple register contexts and method therefor
A data processing system having multiple register contexts is described. One embodiment of the present invention uses a user programmable context control register for each of the multiple register contexts to allow for the mapping of portions of an alternate register context into a current register context. The context control register may also be used to provide for the sharing of common stack pointers among multiple register contexts. Therefore, when operating in a current register context, the context control register may be used to access portions of an alternate register context in place of accessing corresponding portions of the current register context.
1. A data processing system comprising:
a plurality of register contexts;
storage circuitry for storing context control information corresponding to at least a portion of the plurality of register contexts, wherein the storage circuitry comprises a plurality of context control registers, wherein each of the plurality of register contexts comprises a corresponding context control register; and
processing circuitry for selectively accessing a portion of an alternate register context within the plurality of register contexts in place of a corresponding portion of a current register context within the plurality of register contexts, wherein the alternate register context and the portion of the alternate register context are indicated by the context control register corresponding to the current register context; and wherein the context control register corresponding to the current register context comprises a mapping field to identify the portion of the alternate register context and an alternate context field to identify the alternate register context.
2. The data processing system of claim 1 , wherein the portion of the alternate register context comprises a stack pointer.
3. The data processing system of claim 1 , wherein the portion of the alternate register context comprises a set of registers.
4. The data processing system of claim 3 , wherein the set of registers comprises a plurality of general purpose registers.
5. The data processing system of claim 1 , wherein the context control information comprises an enable field wherein, when the enable field is asserted, the processing circuitry accesses the portion of the alternate register context.
6. The data processing system of claim 5 , wherein the context control information comprises a previous context field to identify a previous register context within the plurality of register contexts that was executing previous to the current context register.
7. In a data processing system having a plurality of register contexts, a method comprising:
operating in a first register context within the plurality of register contexts, each of the plurality of register contexts having corresponding context control information, wherein operating in the first register context comprises:
accessing a first portion of the first register context;
selectively accessing a portion of a second register context corresponding to a second portion of the first register context based on the corresponding context control information of the first register context, wherein the corresponding context control information of the first register context identifies the second register context and the portion of the second register context; and wherein each of the corresponding context control information comprises a mapping field to identify the portion of the second register context and an alternate context field to identify the second register context.
8. The method of claim 7 , wherein the portion of the second register context comprises a stack pointer.
9. The method of claim 7 , wherein the portion of the second register context comprises a set of registers.
10. The method of claim 9 , wherein the set of registers comprises a plurality of general purpose registers.
11. The method of claim 8 , wherein the context control information comprises an enable field wherein, when the enable field is asserted, the method comprises accessing the portion of the second register context corresponding to the second portion of the first register context.
12. The method of claim 8 , further comprising:
receiving a context selector;
operating in the second register context based on the context selector; and
selectively accessing a portion of a third register context corresponding to a second portion of the second register context based on corresponding context control information of the second register context.
13. The method of claim 12 , further comprising:
storing a current context into the corresponding context control information of the second register context, the current context corresponding to the second register context; and
storing control information of a saved context into the corresponding context control information of the second register context, the saved context control information corresponding to the first register context.
14. The method of claim 12 , wherein the context selector is received in response to one of an interrupt or a process switch in the data processing system.
15. A data processing system comprising:
a plurality of register contexts, wherein each register context comprises a corresponding context control register having an alternate register context field and a mapping field; and
processing means for selectively accessing a portion of an alternate register context within the plurality of register contexts in place of accessing a corresponding portion of a current register context within the plurality of register contexts, wherein the portion of the alternate register context is defined by the mapping field in the context control register corresponding to the current register context and the alternate register context is defined by the alternate register context field in the context control register corresponding to the current register context.
16. The data processing system of claim 15 , wherein the context control registers are user programmable.
17. The data processing system of claim 15 , wherein the portion of the alternate register context comprises a stack pointer.
18. The data processing system of claim 15 , wherein the portion of the alternate register context comprises a set of registers.
19. The data processing system of claim 15 , further comprising a control register file for storing the context control registers.
20. The data processing system of claim 1 , wherein each of the plurality of context control registers comprises an alternate context field to identify an alternate register context and a mapping field to identify a portion of the alternate register context.
21. The method of claim 8 , wherein the corresponding context information of each of the plurality of register contexts includes an alternate context field to identify an alternate context of the plurality of registers contexts and a mapping field to identify a portion of the alternate context identified by the alternate context field.