Reply To: Time Scale

[Caleb Chamberlain]

The extra delay is a result of the way the UM7’s architecture is set up. Internally, the UM7 uses a cooperative multi-tasking architecture. On each iteration through its main loop, the UM7 samples sensors (if they are ready), computes state estimates if needed, and initiates transmission of packets that need to be sent. Packet transmission is not driven asynchronously – meaning, when it comes time to transmit the next packet, it has to finish whatever it is currently doing before it pushes the packet to the serial transmit buffer.

Another factor affecting delay is the number of packets being transmitted and the baud rate of the port. When packets need to be transmitted, they are added to a queue, and the packets are sent to the serial hardware one at a time by the DMA controller. The more packets that are being transmitted, and the lower the baud rate, the longer the delay.

So yes, you can expect the timestamps to be more than a couple microseconds away from nominal.