In-band communication interface power management fencing

1. An apparatus comprising:

an interface configured to manage a plurality of transfer channels, each transfer channel comprising a first signal that indicates whether the apparatus is ready to service a request;

a processing circuit configured to service received requests from a source via the interface; and

a power control circuit; and

wherein, based at least in part on an event that causes a change in whether the processing circuit services requests, the power control circuit is configured to:

adjust a power management state of the processing circuit by autonomously performing a power up or a power down of the processing circuit independently of the source or another circuit; and

maintain the first signal of each of the plurality of transfer channels in a state that indicates whether the apparatus is ready to service a request based on the power management state of the processing circuit.

2. The apparatus as recited in claim 1 , wherein the interface is further configured to manage, on a plurality of transaction channels different from the plurality of transfer channels, an exchange with the source of one or more of data targeted by a request being serviced and a status of completion of the request.

3. The apparatus as recited in claim 1 , wherein based at least in part on the event comprising an idle condition, the power control circuit is further configured to:

autonomously power down the processing circuit to a non-operational state that stops servicing requests; and

maintain the first signal of each of the plurality of transfer channels in a state that indicates the apparatus is not ready to service a request.

4. The apparatus as recited in claim 3 , wherein detecting the idle condition has occurred comprises a request of a particular type not being received for a threshold period of time.

5. The apparatus as recited in claim 4 , wherein each of the plurality of transfer channels further comprises one of a plurality of second signals that indicates whether the request of the particular type is ready to be sent.

6. The apparatus as recited in claim 1 , wherein based at least in part on the event comprising a power up condition, the power control circuit is further configured to:

autonomously power up the processing circuit to an operational state that allows servicing of requests; and

maintain the first signal of each of the plurality of transfer channels in a state that indicates the apparatus is ready to service a request.

7. The apparatus as recited in claim 6 , wherein the power up condition comprises a number of received requests exceeds a threshold.

8. A method comprising:

managing, by a destination, a plurality of transfer channels comprising a plurality of first signals, each transfer channel comprising one of the plurality of first signals that indicates whether the destination is ready to service a request;

receiving, by the destination, requests from a source via an interface;

in response to an event has occurred that causes a change in whether the destination services requests:

adjusting a power management state of the destination by autonomously performing a power up or a power down of the destination independently of the source or another circuit; and

maintaining each of the plurality of first signals of the plurality of transfer channels in a state that indicates whether the destination is ready to service a request based on the power management state of the destination.

9. The method as recited in claim 8 , wherein, in response to each of the plurality of first signals of the plurality of transfer channels indicate, for a threshold period of time, the destination is not ready to service requests, the method further comprises a source autonomously reducing generation of requests to be serviced by the destination.

10. The method as recited in claim 8 , wherein in response to the event that has occurred comprises an idle condition, the method further comprises:

autonomously powering down the destination to a non-operational state that stops servicing requests; and

maintaining each of the plurality of first signals of the plurality of transfer channels in a state that indicates the destination is not ready to service a request.

11. The method as recited in claim 10 , wherein the idle condition has occurred comprises a request of a particular type is not ready to be sent to the destination by a source for a threshold period of time.

12. The method as recited in claim 11 , wherein each of the plurality of transfer channels further comprises one of a plurality of second signals that indicates whether the request of the particular type is ready to be sent to the destination for servicing.

13. The method as recited in claim 8 , wherein in response to the event comprising a power up condition, the method further comprises:

autonomously powering up the destination to an operational state that allows servicing of requests; and

maintaining each of the first signals of the plurality of transfer channels in a state that indicates the destination is ready to service a request.

14. The method as recited in claim 13 , wherein the power up condition comprises a number of received requests exceeds a threshold.

15. A computing system comprising:

a destination; and

a plurality of transfer channels comprising a plurality of first signals coupled to the destination, each transfer channel comprising one of the plurality of first signals that indicates whether the destination is ready to service a request;

wherein the destination comprises:

a processing circuit configured to service received requests from a source; and

a power control circuit; and

wherein, based at least in part on an event has occurred that causes a change in whether the processing circuit services requests, the power control circuit is configured to:

adjust a power management state of the processing circuit by autonomously performing a power up or a power down of the processing circuit independently of the source or another circuit; and

maintain each of the plurality of first signals of the plurality of transfer channels in a state that indicates whether the processing circuit is ready to service a request based on the power management state of the processing circuit.

16. The computing system as recited in claim 15 , wherein based at least in part on the event that has occurred comprises an idle condition, the power control circuit is further configured to:

autonomously power down the processing circuit to a non-operational state that stops servicing requests; and

maintain each of the plurality of first signals of the plurality of transfer channels in a state that indicates the destination is not ready to service a request.

17. The computing system as recited in claim 16 , wherein the idle condition has occurred comprises a request of a particular type is not ready to be sent from a source to the destination for a threshold period of time.

18. The computing system as recited in claim 17 , wherein each of the plurality of transfer channels further comprises one of a plurality of second signals that indicates whether the request of the particular type is ready to be sent to the destination for servicing.

19. The computing system as recited in claim 15 , wherein based at least in part on the event has occurred comprises a power up condition, the power control circuit is further configured to:

autonomously power up the processing circuit to an operational state that allows servicing of requests; and

maintain each of the first signals of the plurality of transfer channels in a state that indicates the destination is ready to service a request.

20. The computing system as recited in claim 19 , wherein the power up condition comprises a number of received requests exceeds a threshold.