Maintaining coordination following a wireless reset
An electronic device that reduces relative drift is described. In particular, an interface circuit in the electronic device may calculate, based on differences between transmit times when packets were transmitted by a second electronic device and receive times of the packets, relative drift as a function of time between a clock in the interface circuit and a second clock in the second electronic device. Then, the interface circuit may adjust, based on the relative drift, a clock circuit that provides the clock to eliminate the relative drift, and may store the adjustments to the clock circuit. Furthermore, when a wireless reset occurs, the interface circuit may adapt the clock circuit based on the stored adjustments to reduce the relative drift while the interface circuit restores frequency lock with the second clock based on additional packets with additional transmit times that are received from the second electronic device.
1. An electronic device, comprising:
one or more antennas;
a clock circuit that is configured to provide a clock; and
an interface circuit communicatively coupled to the one or more antennas and the clock circuit, wherein the electronic device is configured to:
receive, from the one or more antennas, packets associated with a second electronic device, wherein a given packet includes a transmit time, based on a second clock in the second electronic device, when the second electronic device transmitted the given packet;
store receive times when the packets were received, wherein the receive times are based on the clock;
calculate, based on differences between the transmit times and the receive times, relative drift as a function of time between the clock and the second clock;
adjust, based on the relative drift, the clock circuit to eliminate the relative drift;
store adjustments to the clock circuit determined in the adjusting; and
when the interface circuit or a second interface circuit in the second electronic device is reset, adapt the clock circuit based on the stored adjustments to reduce the relative drift while the electronic device restores frequency lock with the second clock based on additional packets with additional transmit times that are received from the one or more antennas.
2. The electronic device of claim 1 , wherein the clock circuit further comprises:
an oscillator configured to provide a reference clock; and
a frequency-locked-loop (FLL) circuit, coupled to the oscillator, configured to generate the clock based on the reference clock; and
wherein the adjustments are applied to a seed of a first synthesizer in the FLL.
3. The electronic device of claim 2 , wherein the FLL includes a second synthesizer that is configured to track the adjustments to the first synthesizer.
4. The electronic device of claim 1 , wherein restoring the frequency lock occurs over a time interval; and
wherein, prior to storing the adjustments, the electronic device is configured to average the adjustments over a time scale corresponding to the time interval.
5. The electronic device of claim 1 , wherein the transmit time is included in the given packet in one of: a payload; and a media access control (MAC) header.
6. The electronic device of claim 1 , wherein the transmit times include second counter values corresponding to the second clock and the receive times include counter values corresponding to the clock;
wherein, when the interface circuit or the second interface circuit is reset, a counter in the electronic device that provided the counter values corresponding to the clock is reset; and
wherein the electronic device includes a sample-and-hold circuit that is configured to mirror a current counter value of the counter when the interface circuit or the second interface circuit is reset.
7. The electronic device of claim 1 , wherein the packets include control packets.
8. The electronic device of claim 1 , wherein the receive times are associated with a wireless ranging capability of the interface circuit.
9. A method for reducing relative drift, comprising:
by an electronic device:
receiving, from one or more antennas in the electronic device, packets associated with a second electronic device, wherein a given packet includes a transmit time, based on a second clock in the second electronic device, when the second electronic device transmitted the given packet;
storing receive times when the packets were received, wherein the receive times are based on a clock in the electronic device;
calculating, based on differences between the transmit times and the receive times, the relative drift as a function of time between the clock and the second clock;
adjusting, based on the relative drift, a clock circuit in the electronic device that provides the clock to eliminate the relative drift;
storing adjustments to the clock circuit determined in the adjusting; and
when the interface circuit or a second interface circuit in the second electronic device is reset, adapting the clock circuit based on the stored adjustments to reduce the relative drift while the electronic device restores frequency lock with the second clock based on additional packets with additional transmit times that are received from the one or more antennas.
10. An electronic device, comprising:
one or more antennas;
a clock circuit that is configured to provide a clock; and
an interface circuit communicatively coupled to the one or more antennas, wherein the electronic device is configured to:
receive, from the one or more antennas, packets associated with a second electronic device, wherein a given packet includes a transmit time, based on a second clock in the second electronic device, when the second electronic device transmitted the given packet;
store receive times when the packets were received, wherein the receive times are based on the clock;
calculate, based on differences between the transmit times and the receive times, relative drift as a function of time between the clock and the second clock;
adjust, based on the relative drift, the clock circuit to eliminate the relative drift;
store adjustments to the clock circuit determined in the adjusting; and
adapt the clock circuit based on the stored adjustments to reduce the relative drift during a reset, the adapting being performed on a longer time scale than the adjusting.
11. The electronic device of claim 10 , wherein the adapting is performed periodically.
12. The electronic device of claim 10 , wherein the adapting reduces the relative drift when the interface circuit or a second interface circuit in the second electronic device is reset and while the electronic device restores frequency lock with the second clock based on additional packets with the additional transmit times that are received from the one or more antennas.
13. The electronic device of claim 12 , wherein restoring the frequency lock occurs over a time interval; and
wherein, prior to storing the adjustments, the electronic device is configured to average the adjustments over a time scale corresponding to the time interval.
14. The electronic device of claim 12 , wherein the transmit times include second counter values corresponding to the second clock and the receive times include counter values corresponding to the clock;
wherein, when the interface circuit or the second interface circuit is reset, a counter in the electronic device that provided the counter values corresponding to the clock is reset; and
wherein the electronic device includes a sample-and-hold circuit that is configured to mirror a current counter value of the counter when the interface circuit or the second interface circuit is reset.
15. The electronic device of claim 10 , wherein the clock circuit further comprises:
an oscillator configured to provide a reference clock; and
a frequency-locked-loop (FLL) circuit, coupled to the oscillator, configured to generate the clock based on the reference clock; and
wherein the adjustments are applied to a seed of a first synthesizer in the FLL.
16. The electronic device of claim 15 , wherein the FLL includes a second synthesizer that is configured to track the adjustments to the first synthesizer.
17. The electronic device of claim 10 , wherein the transmit time is included in the given packet in one of: a payload; and a media access control (MAC) header.
18. The electronic device of claim 10 , wherein the packets include control packets.
19. The electronic device of claim 10 , wherein the receive times are associated with a wireless ranging capability of the interface circuit.
20. A method for reducing relative drift, comprising:
by an electronic device:
receiving, from one or more antennas in the electronic device, packets associated with a second electronic device, wherein a given packet includes a transmit time, based on a second clock in the second electronic device, when the second electronic device transmitted the given packet;
storing receive times when the packets were received, wherein the receive times are based on a clock in the electronic device;
calculating, based on differences between the transmit times and the receive times, the relative drift as a function of time between the clock and the second clock;
adjusting, based on the relative drift, a clock circuit in the electronic device that provides the clock to eliminate the relative drift;
storing adjustments to the clock circuit determined in the adjusting; and
adapting the clock circuit based on the stored adjustments to reduce the relative drift during a reset, the adapting being performed on a longer time scale than the adjusting.