Electronic devices and operational methods that change clock frequencies that are applied to a central processing unit and a main system bus

1. A method of operating an electronic device that includes a Central Processing Unit (CPU) and a main system bus, the method comprising:

decreasing an operational clock frequency of the CPU from a first clock frequency and of the main system bus from a second clock frequency that is lower than the first clock frequency, to a third clock frequency that is lower than the second clock frequency, and decreasing an operating voltage of the CPU, responsive to an operational mode of the CPU switching to an idle mode, wherein the switching of the operational mode of the CPU to an idle mode triggers the decreasing of the operational clock frequency of the CPU and of the main system bus; and

increasing the operational clock frequency of the CPU and of the main system bus from the third clock frequency to the first clock frequency and to the second clock frequency, respectively, and increasing the operating voltage of the CPU, responsive to the operational mode of the CPU switching to an active mode,

wherein the electronic device further includes a display and wherein increasing the operational clock frequency of the CPU and of the main system bus and increasing the operating voltage of the CPU are performed during an interrupt service routine generated in synchronization with a vertical synchronization signal of the display, and

further wherein increasing the operational clock frequency of the CPU and of the main system bus and increasing the operating voltage of the CPU are performed during a horizontal scan period of the display.

2. A method according to claim 1 wherein the operational clock frequency of the CPU is increased after increasing the operational clock frequency of the main system bus.

3. A method according to claim 2 wherein increasing the operational clock frequency of the CPU comprises deactivating a dynamic voltage scaling functionality of the CPU.

4. A method according to claim 1 wherein operational clock frequency of the CPU is increased before increasing the operational clock frequency of the main system bus.

5. A method according to claim 1 wherein decreasing an operational frequency of the CPU from the first clock frequency and of the main system bus from the second clock frequency comprises:

matching the operational clock frequency of the CPU with the operational clock frequency of the main system bus after decreasing the operational clock frequency of the main system bus to the third clock frequency.

6. A method according to claim 5 wherein matching the operational clock frequency of the CPU with the operational clock frequency of the main system bus comprises activating a dynamic voltage scaling functionality of the CPU.

7. A method according to claim 1 wherein decreasing an operational frequency of the CPU from the first clock frequency and of the main system bus from the second clock frequency comprises:

decreasing the operational clock frequency of the main system bus to the third clock frequency after matching the operational clock frequency of the CPU with the operational clock frequency of the main system bus.

8. A method according to claim 1 wherein the electronic device further includes a secondary bus and wherein the method further comprises operating the secondary bus at the third clock frequency.

9. A method according to claim 8 wherein the secondary bus corresponds to an AMBA advanced Peripheral bus (APB).

10. A method according to claim 1 wherein the main system bus corresponds to an AMBA High-performance peripheral bus (AHB).

11. A method of operating an electronic device that includes a Central Processing Unit (CPU) and a main system bus, the method comprising:

decreasing an operational clock frequency of the CPU from a first clock frequency and of the main system bus from a second clock frequency that is lower than the first clock frequency, to a third clock frequency that is lower than the second clock frequency, and decreasing an operating voltage of the CPU, responsive to an operational mode of the CPU switching to an idle mode, wherein the switching of the operational mode of the CPU to an idle mode triggers the decreasing of the operational clock frequency of the CPU and of the main system bus; and

wherein the electronic device further includes a display and wherein the method further comprises providing the second clock frequency to the display; dividing the second clock frequency that is provided to the display; and providing the divided second clock frequency to a display driver; and

further wherein decreasing the operational clock frequency of the CPU and of the main system bus and decreasing the operating voltage of the CPU are performed during an interrupt service routine generated in synchronization with a vertical synchronization signal of the display; and

further wherein decreasing the operational clock frequency of the CPU and of the main system bus and decreasing the operating voltage of the CPU are performed during a horizontal scan period of the display.

12. A method according to claim 11 , wherein decreasing an operational frequency of the CPU from the first clock frequency and of the main system bus from the second clock frequency comprises:

matching the operational clock frequency of the CPU with the operational clock frequency of the main system bus after decreasing the operational clock frequency of the main system bus to the third clock frequency.

13. A method according to claim 12 wherein matching the operational clock frequency of the CPU with the operational clock frequency of the main system bus comprises activating a dynamic voltage scaling functionality of the CPU.

14. A method according to claim 11 , wherein decreasing an operational frequency of the CPU from the first clock frequency and of the main system bus from the second clock frequency comprises:

decreasing the operational clock frequency of the main system bus to the third clock frequency after matching the operational clock frequency of the CPU with the operational clock frequency of the main system bus.

15. A method according to claim 11 , wherein the electronic device further includes a secondary bus and wherein the method further comprises operating the secondary bus at the third clock frequency.

16. A method according to claim 15 , wherein the secondary bus corresponds to an AMBA advanced Peripheral bus (APB).

17. A method according to claim 11 , wherein the main system bus corresponds to an AMBA High-performance peripheral bus (AHB).