Systems and methods of time synchronization

1 . A system comprising an electronic device and a powered accessory wherein:

the electronic device comprises:

power regulation circuitry that receives power from the powered accessory;

a first communication system that communicates with the powered accessory;

an internal clock; and

a first processing system coupled to the first communication system and the internal clock, wherein upon connection of the electronic device to the powered accessory, the first processing system sends a first time update request to the powered accessory and updates the internal clock based on a first time update received from the powered accessory;

the powered accessory lacks a network connection and comprises:

an energy storage device that delivers power to the electronic device;

a second communication system that communicates with the electronic device;

a real time clock; and

a second processing system coupled to the second communication system and the real time clock, wherein upon connection of the electronic device to the powered accessory and receiving the first time update request from the electronic device, the second processing system sends the first time update to the electronic device; and

wherein the electronic device further comprises a network interface coupled to the first processing system and the first processing system sends a second time update request to a network time protocol server via the network interface according to a network time protocol and receives a second time update from the network time protocol server via the network interface according to the network time protocol.

2 . The system of claim 1 wherein the first time update request takes the form of a network time protocol packet.

3 . The system of claim 2 wherein the first time update takes the form of the network time protocol packet.

4 . The system of claim 1 wherein:

the first processing system sends a third time update to the powered accessory via the first communication system;

the third time update is based on the second time update received from the network time protocol server; and

the second processing system updates the real time clock based on the third time update.

5 . An electronic device comprising:

power regulation circuitry that receives power from a powered accessory;

a first communication system that communicates with the powered accessory;

an internal clock; and

a first processing system coupled to the first communication system and the internal clock; and

a network interface coupled to the first processing system;

wherein upon connection of the electronic device to the powered accessory, the first processing system:

sends a first time update request to the powered accessory and updates the internal clock based on a first time update received from the powered accessory;

sends a second time update request to a network time protocol server via the network interface according to a network time protocol;

receives a second time update from the network time protocol server via the network interface according to the network time protocol; and

updates the internal clock based on the second time update.

6 . The electronic device of claim 5 wherein the first time update request and first time update take the form of a network time protocol packet.

7 . The electronic device of claim 6 wherein the first time update request and first time update do not correspond to a network time protocol.

8 . The electronic device of claim 5 wherein the first time update includes information about present time, communication delay between the electronic device and the powered accessory, and a powered accessory clock uncertainty value.

9 . The electronic device of claim 8 wherein the first processing system does not update the internal clock if the powered accessory clock uncertainty value exceeds a threshold.

10 . The electronic device of claim 5 wherein prior to sending the first time update request to the powered accessory, the first processing system updates the internal clock using an internally recovered time.

11 . The electronic device of claim 10 wherein the internally recovered time is based on a file system timestamp associated with the first processing system.

12 . The electronic device of claim 5 wherein the first processing system sends a third time update to the powered accessory via the first communication system, and the third time update is based on the second time update received from the network time protocol server.

13 . A powered accessory that supplies power an electronic device and lacks a network connection, the powered accessory comprising:

an energy storage device that delivers power to the electronic device;

a communication system that communicates with the electronic device;

a real time clock; and

a processing system coupled to the communication system and the real time clock;

wherein upon connection of the electronic device to the powered accessory and receiving a first time update request from the electronic device, the processing system:

sends a first time update to the electronic device;

receives a second time update via the communication system from the electronic device; and

updates the real time clock based on the second time update.

14 . The powered accessory of claim 13 wherein the first time update request and first time update take the form of a network time protocol packet.

15 . The powered accessory of claim 14 wherein the first time update request and first time update do not correspond to a network time protocol.

16 . The powered accessory of claim 13 wherein the first time update includes information about present time, communication delay between the electronic device and the powered accessory, and a powered accessory real time clock uncertainty value.

17 . The powered accessory of claim 13 wherein the processing system detects a reset that might affect the real time clock and in response thereto sets an uncertainty value associated with the real time clock to a maximum value.