Microcontroller clock calibration using data transmission from an accurate third party

• US 20090161806A1
• Filed: 12/19/2007
• Published: 06/25/2009
• Est. Priority Date: 12/19/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Kalayjian, Nicholas R., Rabu, Stanley, Tikalsky, Terry, Ananny, John M.
• Granted Patent: US 8,559,575 B2
• Time in Patent Office: Days
• US Class Current: 375/354
• CPC Class Codes: G04G 7/00 Synchronisation radio-controlled time-pieces G04R
• CPC Class Codes: G06F 13/4045 where the bus bridge performs an extender function

Abstract

Systems and methods are provided for calibrating the internal oscillator of a microcontroller from a remote clock source. In some embodiments, an electronic device can request timing information from a third party device using a timing independent signal. The timing information received from the third party device may be used to calibrate the microcontroller clock of the electronic device. In some embodiments, the internal oscillator may be calibrated based on timing information received from multiple third party devices. Once calibrated, the microcontroller may initiate timing dependent communication with other electronic devices using a timing dependent protocol, such as a serial protocol.

Claims

1. A method of enabling timing dependent communication between a first electronic device and a second electronic device, comprising:

transmitting a timing independent signal from the first device to a third party device to request transmission of timing information;

calibrating a clock source of the first device based on the timing information transmitted from the third party device and received by the first device; and

conducting the timing dependent communication between the first device and the second device, wherein the data rate of the timing dependent communication is based on a clock rate of the clock source.

2. The method of claim 1, wherein the transmitting the timing independent signal comprises pulsing a voltage of the timing independent signal.

3. The method of claim 1, wherein the third party device comprises a reliable clock source, and wherein the timing information is derived from the reliable clock source.

4. The method of claim 3, wherein the reliable clock source is a crystal oscillator.

5. The method of claim 1, further comprising transmitting a timing dependent signal from the first device to the third party device to end transmission of the timing information.

6. The method of claim 1, further comprising:

transmitting a predetermined packet from the first device to the third party device using a timing dependent protocol;

ending the calibrating of the clock source in response to the first device receiving an acknowledgement of receipt of the predetermined packet from the third party device; and

retransmitting the predetermined packet from the first device to the third party device when the acknowledgement is not received by the first device.

7. The method of claim 1, wherein the timing independent signal is a first timing independent signal, the method further comprising:

transmitting a second timing independent signal from the first device to the third party device subsequent to the transmitting the first timing independent signal to request transmission of additional timing information; and

recalibrating the clock source based on the additional timing information transmitted from the third party device and received by the first device.

8. The method of claim 7, wherein the second timing independent signal is automatically transmitted a predetermined amount of time after the transmitting the first timing independent signal.

9. The method of claim 7, wherein the second timing independent signal is transmitted after the conducting the timing dependent communication ceases for a timeout period of time.

10. A method of transmitting timing information from a first electronic device to a second electronic device, wherein the first device comprises a reliable clock source, and wherein the second device comprises a microcontroller with an internal oscillator, the method comprising:

receiving a timing independent signal from the second device with the first device;

detecting a request for the timing information from the received timing independent signal with the first device; and

transmitting the timing information from the first device to the second device, wherein the timing information is derived from the reliable clock source, and wherein the timing information is used by the second device to calibrate the internal oscillator of the microcontroller.

11. The method of claim 10, wherein the detecting the request comprises detecting a voltage change of the timing independent signal.

12. The method of claim 10, further comprising powering the first device using the timing independent signal.

13. A system, comprising:

a third party device comprising a reliable clock source, wherein the third party device is configured to transmit timing information derived from the reliable clock source in response to receiving a timing independent request; and

a first electronic device coupled to the third party device, wherein the first electronic device comprises a microcontroller with an internal oscillator, and wherein the first electronic device is configured to;

transmit the timing independent request to the third party device; and

calibrate the internal oscillator with the timing information received from the third party device.

14. The system of claim 13, wherein the third party device is a wireless headset, and wherein the reliable clock source is a crystal oscillator.

15. The system of claim 13, wherein the first electronic device is a docking device adapted to be an accessory device for the third party device.

16. The system of claim 13, further comprising a second electronic device for communicating with the first device using a timing dependent protocol.

17. The system of claim 16, wherein the second electronic device is a portable media player.

18. An electronic device, comprising:

a first communication link for transmitting a request for timing information using a timing independent protocol;

a second communication link for receiving the timing information; and

a microcontroller for controlling operations of the electronic device, wherein an internal oscillator of the microcontroller is calibrated based on the received timing information.

19. The electronic device of claim 18, wherein the first communication link is adapted for providing power to a second electronic device.

20. The electronic device of claim 18, further comprising:

a regulator for providing a first voltage and a second voltage, wherein the first voltage is different from the second voltage; and

a switch for selectively providing one of the first voltage and the second voltage to the first communication link, wherein the request for the timing information is transmitted by changing a state of the switch for a period of time.

21. A method of calibrating a clock source of a first electronic device for use in enabling timing dependent communication between the first device and a second electronic device, the method comprising:

transmitting a request for timing signals from the first device to a plurality of third party devices using a timing independent protocol;

receiving a plurality of timing signals with the first device from the plurality of third party devices in response to the request;

deriving timing information with the first device from at least a subset of the timing signals; and

calibrating the clock source based on the timing information.

22. The method of claim 21, wherein the clock source is an internal oscillator of a microcontroller within the first device.

23. The method of claim 21, wherein the deriving the timing information comprises averaging the at least a subset of the timing signals.

24. The method of claim 21, wherein the deriving the timing information comprises selecting one of the plurality of timing signals based on at least one of the magnitudes of the timing signals and priorities of the ports of the first device that obtained each of the plurality of timing signals.

25. The method of claim 21, wherein the plurality of timing signals are received with the first device from at least a subset of the plurality of third party devices.