Data processing system having selective invalidation of snoop requests and method therefor
View Patent ↗A data processing system includes a system interconnect, a processor coupled to the system interconnect, and a cache coherency manager (CCM) coupled to the system interconnect. The processor includes a cache. A method includes generating, by the CCM, one or more snoop requests to the cache of the processor; storing the one or more snoop requests to the cache of the processor into a snoop queue; setting a cache enable indicator to indicate that the cache of the processor is to be disabled; in response to setting the cache enable indicator to indicate that the cache of the processor is to be disabled, selectively invalidating the one or more snoop requests to the cache of the processor, wherein the selectively invalidating is performed based on an invalidate snoop queue indicator of the processor; and disabling the cache.
1. In a data processing system having a system interconnect, a first processor coupled to the system interconnect, and a cache coherency manager (CCM) coupled to the system interconnect, wherein the first processor comprises a first cache, a method comprising:
generating, by the CCM, one or more first snoop requests to the first cache of the first processor;
storing the one or more first snoop requests to the first cache of the processor into a first snoop queue;
setting a first cache enable indicator to indicate that the first cache of the first processor is to be disabled;
in response to setting the first cache enable indicator to indicate that the first cache of the first processor is to be disabled, selectively invalidating the one or more first snoop requests to the first cache of the first processor, wherein the selectively invalidating includes invalidating the one or more first snoop requests when a first invalidate snoop queue indicator of the first processor has a first state, and selectively invalidating also includes not invalidating and completing the one or more first snoop requests when the first invalidate snoop queue indicator has a second state that is different from the first state; and
disabling the first cache.
2. The method of claim 1 , further comprising:
providing, by the first processor, a cache enable signal to the CCM, wherein, in response to the first cache enable indicator indicating that the first cache is to be disabled, the first processor sets the cache enable signal to indicate to the CCM that the first cache is to be disabled.
3. The method of claim 2 , wherein the CCM comprises the first snoop queue, and wherein the method further comprises:
providing, by the first processor, an invalidate snoop queue signal to the CCM indicating whether or not to invalidate the one or more first snoop requests to the first cache of the processor.
4. The method of claim 3 , wherein:
when the cache enable signal transitions from indicating that the first cache is enabled to indicating that the first cache is to be disabled, the one or more first snoop requests to the first cache of the first processor in the first snoop queue are invalidated if the invalidate snoop queue signal has a first state and the one or more first snoop requests to the first cache of the first processor are not invalidated if the invalidate snoop queue signal has a second state.
5. The method of claim 1 , wherein each of the first cache enable indicator and the first invalidate snoop queue indicator is user programmable.
6. The method of claim 1 , wherein the step of disabling the first cache is performed when the first processor enters a low power mode.
7. The method of claim 1 , wherein the step of disabling the first cache is performed when the first processor enters a test mode.
8. The method of claim 1 , wherein the data processing system comprises a second processor coupled to the system interconnect, wherein the second processor comprises a second cache, wherein the method further comprises:
generating, by the CCM, one or more second snoop requests to the second cache of the second processor;
storing the one or more second snoop requests to the second cache of the second processor into a second snoop queue;
setting a second cache enable indicator of the second processor to indicate that the second cache of the second processor is to be disabled;
in response to setting the second cache enable indicator to indicate that the second cache of the second processor is to be disabled, selectively invalidating the one or more second snoop requests to the second cache of the second processor, wherein the selectively invalidating is performed based on a second invalidate snoop queue indicator of the second processor; and
disabling the second cache of the second processor.
9. The method of claim 8 , further comprising:
providing, by the second processor, to the CCM a second cache enable signal and a second invalidate snoop queue signal.
10. The method of claim 9 , wherein:
the first invalidate snoop queue indicator of the first processor indicates that the one or more first snoop queue requests to the first cache of the first processor are invalidated in response to setting the first cache enable indicator to indicate that the first cache of the first processor is to be disabled, and
the second invalidate snoop queue indicator of the second processor indicates that the one or more snoop requests to the second cache of the second processor are not invalidated in response to setting the second cache enable indicator to indicate that the second cache of the second processor is to be disabled.
11. In a data processing system having a system interconnect, a processor coupled to the system interconnect, and a cache coherency manager (CCM) coupled to the system interconnect, wherein the processor comprises a cache, a method comprising:
generating, by the CCM, one or more snoop requests to the cache of the processor wherein the CCM comprises a snoop queue;
storing the one or more snoop requests to the cache of the processor into the snoop queue;
providing, by the processor, an invalidate snoop queue signal to the CCM based on an invalidate snoop queue indicator of the processor, wherein the invalidate snoop queue signal indicates whether or not to invalidate the one or more snoop requests to the cache of the processor;
setting a cache enable indicator to indicate that the cache of the processor is to be disabled;
providing, by the processor, a cache enable signal to the CCM, wherein, in response to the cache enable indicator indicating that the cache is to be disabled, the processor sets the cache enable signal to indicate to the CCM that the cache is to be disabled;
in response to setting the cache enable indicator to indicate that the cache of the processor is to be disabled, selectively invalidating the one or more snoop requests to the cache of the processor, wherein the selectively invalidating is performed based on the invalidate snoop queue indicator of the processor, wherein when the cache enable signal transitions from indicating that the cache is enabled to indicating that the cache is to be disabled:
the one or more snoop requests to the cache of the processor in the snoop queue are invalidated if the invalidate snoop queue signal has a first state, and,
the one or more snoop requests to the cache of the processor are non invalidated and completed prior to the step of disabling the cache if the invalidate snoop queue signal has a second state; and
disabling the cache.
12. A data processing system, comprising:
a system interconnect;
a processor coupled to the system interconnect, wherein the processor comprises:
a cache;
first storage circuitry which stores an invalidate snoop queue indicator; and
second storage circuitry which stores a cache enable indicator; and
a cache coherency manager (CCM) coupled to the system interconnect, the cache coherency manager having a first snoop queue corresponding to the processor, wherein the cache coherency manager generates snoop requests for the processor which are stored in the first snoop queue, wherein, in response to the cache enable indicator being set to indicate that the cache of the processor is to be disabled, the snoop requests for the processor in the first snoop queue are selectively invalidated based on the invalidate snoop queue indicator, wherein selectively invalidating the snoop requests includes invalidating the snoop requests when the invalidate snoop queue indicator of the processor has a first state, and selectively invalidating also includes not invalidating and completing the snoop requests when the invalidate snoop queue indicator has a second state that is different from the first state.
13. The data processing system of claim 12 , wherein the processor provides a cache enable signal, wherein the cache enable signal indicates to the CCM when the cache is to be disabled.
14. The data processing system of claim 13 , wherein the processor provides an invalidate snoop queue signal to the CCM, wherein when the cache enable signal transitions from indicating that the cache is enabled to indicating that the cache is to be disabled, the invalidate snoop queue signal indicates to the CCM whether or not to invalidate the one or more snoop requests to the cache of the processor.
15. The data processing system of claim 12 , wherein the processor comprises a processor snoop queue, wherein, in response to the cache enable indicator indicating that the cache is to be disabled, the processor snoop queue is selectively invalidated based on the invalidate snoop queue indicator.
16. The data processing system of claim 12 , further comprising:
a second processor coupled to the system interconnect, wherein the second processor comprises:
a second cache;
third storage circuitry which stores a second invalidate snoop queue indicator; and
fourth storage circuitry which stores a second cache enable indicator;
wherein the cache coherency manager has a second snoop queue corresponding to the second processor, wherein the cache coherency manager generates snoop requests for the second processor which are stored in the second snoop queue, wherein, in response to the second cache enable indicator being set to indicate that the second cache of the second processor is to be disabled, the snoop requests for the second processor in the second snoop queue are selectively invalidated based on the second invalidate snoop queue indicator.
17. The data processing system of claim 16 , wherein:
the second processor provides a second cache enable signal, wherein the second cache enable signal indicates to the CCM when the second cache is to be disabled; and
the second processor provides a second invalidate snoop queue signal to the CCM, wherein when the second cache enable signal transitions from indicating that the second cache is enabled to indicating that the second cache is to be disabled, the second invalidate snoop queue signal indicates to the CCM whether or not to invalidate the snoop requests for the second processor in the second snoop queue.
18. A data processing system, comprising:
a system interconnect;
a processor coupled to the system interconnect, wherein the processor comprises:
a cache;
first storage circuitry which stores an invalidate snoop queue indicator; and
second storage circuitry which stores a cache enable indicator;
a cache coherency manager (CCM) coupled to the system interconnect, the cache coherency manager having a first snoop queue corresponding to the processor, wherein the cache coherency manager generates snoop requests for the processor which are stored in the first snoop queue;
a cache enable signal provided from the processor to the CCM based on the cache enable indicator, wherein the cache enable signal indicates to the CCM when the cache is to be disabled;
an invalidate snoop queue signal provided from the processor to the CCM based on the invalidate snoop queue indicator, wherein when the cache enable signal transitions from indicating that the cache is enabled to indicating that the cache is to be disabled, the invalidate snoop queue signal indicates to the CCM whether or not to invalidate snoop requests for the processor, wherein, in response to the cache enable signal transitioning from indicating that the cache is enabled to indicating that the cache is to be disabled, the CCM selectively invalidates the snoop requests for the processor in the first snoop queue based on the invalidate snoop queue signal, wherein selectively invalidating the snoop requests includes invalidating the snoop requests when the invalidate snoop queue indicator of the processor has a first state, and selectively invalidating also includes not invalidating and completing the one or more first snoop requests when the invalidate snoop queue indicator has a second state that is different from the first state.
19. The data processing system of claim 18 , wherein the processor comprises a processor snoop queue, wherein, in response to the cache enable indicator indicating that the cache is to be disabled, the processor snoop queue is selectively invalidated based on the invalidate snoop queue indicator.
20. The data processing system of claim 18 , further comprising:
a second processor coupled to the system interconnect, wherein the second processor comprises:
a second cache;
third storage circuitry which stores a second invalidate snoop queue indicator; and
fourth storage circuitry which stores a second cache enable indicator;
a second cache enable signal provided from the second processor to the CCM based on the second cache enable indicator, wherein the second cache enable signal indicates to the CCM when the second cache is to be disabled; and
a second invalidate snoop queue signal provided from the second processor to the CCM based on the second invalidate snoop queue indicator, wherein when the second cache enable signal transitions from indicating that the second cache is enabled to indicating that the second cache is to be disabled, the second invalidate snoop queue signal indicates to the CCM whether or not to invalidate snoop requests for the second processor,
wherein the CCM has a second snoop queue corresponding to the second processor and the CCM generates snoop requests for the second processor which are stored in the second snoop queue, and wherein, in response to the second cache enable signal transitioning from indicating that the second cache is enabled to indicating that the second cache is to be disabled, the CCM selectively invalidates the snoop requests for the second processor in the second snoop queue based on the second invalidate snoop queue signal.