Protecting against memory corruption and system freeze during power state transitions in a multi-power domain system

1. A system comprising:

a switchable power domain configured to selectively be powered on and powered off during operation of the system; and

an always-on power domain configured to remain powered on during operation of the system, the always-on power domain including a power management unit configured to, in response to a shut down condition for powering down the switchable power domain:

determine a state of a bus transaction on a communication bus between the switchable power domain and the always-on power domain, wherein the bus transaction is a transaction from a bus master to a bus slave;

control one or more control signals for controlling the communication bus in order to manipulate completion of the bus transaction to prevent at least one of corruption of data of the bus transaction and a system freeze associated with the bus transaction;

monitor for completion of the bus transaction;

in response to an indication of completion of the bus transaction, power down the switchable power domain;

in response to an absence of the indication of completion within a predetermined time, assert an error signal in response to expiration of the pre-determined time; and

communicate an indication to the bus master that data read from the bus slave is invalid.

2. The system of claim 1 , wherein:

the bus master is integral to the switchable power domain and the bus slave is integral to the always-on power domain; and

the power management unit is further configured to, in response to the shut down condition:

freeze a current state of bus signals from the switchable power domain; and

block further write transactions from the switchable power domain.

3. The system of claim 2 , wherein the power management unit is further configured to, in response to completion of the bus transaction, electrically isolate outputs of the switchable power domain from the always-on power domain.

4. The system of claim 2 , wherein the power management unit is configured to freeze the current state of bus signals from the switchable power domain by disabling a synchronization clock of the bus master.

5. The system of claim 2 , wherein the power management unit is configured to block further write transactions from the switchable power domain by masking a bus transaction active signal associated with the communication bus.

6. The system of claim 1 , wherein:

the bus master is integral to the always-on power domain and the bus slave is integral to the switchable power domain; and

the power management unit is configured to, in response to the shut down condition:

cause a transaction completion signal as seen by the bus master to indicate completion of the transaction.

7. The system of claim 6 , wherein the power management unit is further configured to, in response to the transaction completion signal as seen by the bus master indicating completion of the transaction, power down the switchable power domain.

8. The system of claim 6 , wherein the power management unit is further configured to, in response to completion of the bus transaction, in response to the transaction completion signal as seen by the bus master indicating completion of the transaction, electrically isolate outputs of the switchable power domain from the always-on power domain.

9. A method comprising, in a system comprising a switchable power domain configured to selectively be powered on and powered off during operation of the system and an always-on power domain configured to remain powered on during operation of the system, in response to a shut down condition for powering down the switchable power domain:

determining a state of a bus transaction on a communication bus between the switchable power domain and the always-on power domain, wherein the bus transaction is a transaction from a bus master to a bus slave;

controlling one or more control signals for controlling the communication bus in order to manipulate completion of the bus transaction to prevent at least one of corruption of data of the bus transaction and a system freeze associated with the bus transaction;

monitoring for completion of the bus transaction;

in response to an indication of completion of the bus transaction, powering down the switchable power domain;

in response to an absence of the indication of completion within a predetermined time, asserting an error signal in response to expiration of the pre-determined time; and

communicate an indication to the bus master that data read from the bus slave is invalid.

10. The method of claim 9 , wherein:

the bus master is integral to the switchable power domain and the bus slave is integral to the always-on power domain; and

the method further comprises, in response to the shut down condition:

freezing a current state of bus signals from the switchable power domain; and

blocking further write transactions from the switchable power domain.

11. The method of claim 10 , further comprising, in response to completion of the bus transaction, electrically isolating outputs of the switchable power domain from the always-on power domain.

12. The method of claim 10 , further comprising freezing the current state of bus signals from the switchable power domain by disabling a synchronization clock of the bus master.

13. The method of claim 10 , further comprising blocking further write transactions from the switchable power domain by masking a bus transaction active signal associated with the communication bus.

14. The method of claim 9 , wherein:

the bus master is integral to the always-on power domain and the bus slave is integral to the switchable power domain; and

the method further comprises, in response to the shut down condition:

causing a transaction completion signal as seen by the bus master to indicate completion of the transaction.

15. The method of claim 14 , further comprising, in response to the transaction completion signal as seen by the bus master indicating completion of the transaction, powering down the switchable power domain.

16. The method of claim 14 , further comprising, in response to completion of the bus transaction, in response to the transaction completion signal as seen by the bus master indicating completion of the transaction, electrically isolating outputs of the switchable power domain from the always-on power domain.