Methods and systems for synchrophasing using asynchronous buses
Vehicle systems and methods are provided for synchronizing control modules over a communications bus for synchrophasing propellers. A vehicle electrical system includes a communications bus, a bus control module to transmit a first message over the communications bus, a vehicle control module coupled to the bus control module to identify a first timestamp associated with the first message being transmitted in a first clock domain associated with the vehicle control module and provide a subsequent message to the bus control module including the first timestamp, and an actuator control module coupled to the communications bus to identify a second timestamp associated with the first message being received over the communications bus and determine an adjustment to synchronize a second clock domain associated with the actuator control module with the first clock domain based at least in part on a relationship between the first timestamp and the second timestamp.
1. An electrical system suitable for use with a vehicle, the electrical system comprising:
a communications bus;
a bus control module coupled to the communications bus to transmit a first message over the communications bus and provide an indication of the first message being transmitted;
a first control module coupled to the bus control module to identify a first timestamp associated with the indication in a first clock domain associated with the first control module and provide a subsequent message to the bus control module including the first timestamp; and
a second control module coupled to the communications bus to identify a second timestamp associated with the first message being received over the communications bus, identify the first timestamp contained in the subsequent message, and determine an adjustment to synchronize a second clock domain associated with the second control module based at least in part on a relationship between the first timestamp and the second timestamp, wherein the first control module is configured to provide a command message including a phase angle offset for synchrophasing a propeller coupled an actuator coupled to the second control module at a specified point in time in the first clock domain over the communications bus and the second control module is configured to determine an adjusted time in the second clock domain using the specified point in time and the adjustment and actuate the actuator to a commanded position corresponding to the phase angle offset for the propeller at the adjusted time in the second clock domain.
2. The electrical system of claim 1 , further comprising a second bus control module coupled between the communications bus and the second control module to provide a second indication of the first message being received, wherein the second control module identifies the second timestamp associated with the second indication in the second clock domain.
3. The electrical system of claim 2 , wherein:
the indication of the first message being transmitted comprises a first interrupt signal generated by the bus control module in response to transmitting at least a portion of the first message; and
the second indication of the first message being received comprises a second interrupt signal generated by the second bus control module in response to receiving at least a second portion of the first message.
4. The electrical system of claim 3 , wherein the second control module determines the adjustment based on a difference between the first timestamp associated with the first interrupt signal and the second timestamp associated with the second interrupt signal.
5. The electrical system of claim 4 , wherein the adjustment comprises an offset to a current value of the second clock domain at the second control module.
6. The electrical system of claim 1 , wherein the communications bus comprises an asynchronous bus.
7. The electrical system of claim 1 , wherein the communications bus comprises a controller area network (CAN) bus.
8. The electrical system of claim 7 , wherein the bus control module comprises a CAN controller.
9. The electrical system of claim 8 , wherein the first control module comprises a flight control computer.
10. The electrical system of claim 1 , wherein a rotational speed of the propeller is greater than 100 Hertz (Hz).
11. The electrical system of claim 10 , wherein a data rate of the communications bus is 1 megabit per second (Mbps) or less.
12. The electrical system of claim 1 , further comprising:
a second communications bus; and
a second flight control computer coupled to the second control module over the second communications bus to provide a redundant command message including the phase angle offset for synchrophasing the propeller to the second control module over the second communications bus, wherein the first control module comprises a reference timekeeper flight control computer.
13. The electrical system of claim 12 , wherein the second control module is configured to determine the adjustment to synchronize the second clock domain associated with the second control module based at least in part on a receipt timestamp broadcast by the second flight control computer.
14. A method comprising:
receiving, by a first control module coupled to an asynchronous bus, a first synchronization message over the asynchronous bus from a second control module coupled to the asynchronous bus;
identifying, by the first control module, a first timestamp associated with receipt of the first synchronization message in a first clock domain associated with the first control module;
receiving, by the first control module, a second synchronization message over the asynchronous bus from the second control module, the second synchronization message including a second timestamp associated with transmission of the first synchronization message in a second clock domain associated with the second control module;
determining, by the first control module, an adjustment to synchronize the first clock domain with the second clock domain based on a relationship between the first timestamp and the second timestamp; and
operating, by the first control module, a propeller to a commanded phase angle at an adjusted time in the first clock domain corresponding to a specified point in time in the second clock domain based on the adjustment.
15. The method of claim 14 , wherein determining the adjustment comprises calculating an offset to be applied to a current time value in the first clock domain to be equal a reference time value in the second clock domain.
16. The method of claim 14 , wherein a bus control module is coupled between the first control module and the asynchronous bus, wherein identifying the first timestamp comprises the first control module recording a time value in the first clock domain when an interrupt signal is generated by the bus control module in response to receiving at least a portion of the first synchronization message over the asynchronous bus.
17. The method of claim 16 , wherein a second bus control module is coupled between the second control module and the asynchronous bus, wherein the second timestamp comprises a recorded time value in the second clock domain when a second interrupt signal is generated by the second bus control module in response to transmitting at least a second portion of the first synchronization message over the asynchronous bus.
18. A computer-readable medium having computer-executable instructions stored thereon that, when executed by a processing system, cause the processing system to:
identify a first timestamp in a first clock domain associated with a first control module corresponding to transmission of a synchronization message over an asynchronous bus;
identify a second timestamp in a second clock domain associated with a second control module corresponding to receipt of the synchronization message over the asynchronous bus; and
determining an offset to synchronize the second clock domain with the first clock domain based on a relationship between the first timestamp and the second timestamp, resulting in an adjusted reference time in the second clock domain, wherein an actuator coupled to the second control module is operated in accordance with the adjusted reference time and the second control module operates the actuator to actuate a propeller to a commanded phase angle offset at a specified point in time in the first clock domain using the adjusted reference time.
19. The computer-readable medium of claim 18 , wherein the asynchronous bus comprises a controller area network (CAN) bus.
20. The computer-readable medium of claim 19 , wherein the first control module comprises a flight control computer and the second control module comprises an actuator control module.