Reply To: Time Scale

[Caleb Chamberlain]

Hi Andrey,

No, the main loop runs continuously, and independently of the system time. The system time is maintained by a hardware counter that runs continuously. Each time through the main loop, the system checks the system time to determine what, if any, events should be executed – including transmission of packets.

MOST of the time, the core is busy estimating states in the extended kalman filter. So here is the order of events that would cause delay:

1) The system checks the current time. No packets need to be transmitted.
2) The system samples sensors
3) The system takes the new sensor data and computes updated states
4) Greater than 1 millisecond has passed since the last time we checked the time. We check again. It is now past time to transmit a COM packet.
5) The packet TX task is added to a queue, along with all other TX packets. The packet is transmitted as soon as the UART is available.
6) When the packet is transmitted, it takes the most recent data, which will have been sampled after the 20 millisecond target period.