Cyton Timestamp generation

BioPotentialBioPotential
edited February 2020 in Cyton

Was wondering how are timestamps generated in the Cyton device?
Are the timestamps being generated by the PIC32 chip, I don't see any RTC chip on the Cyton, so is the clock synchronised with the PC side? I mean does the PC side send the clock to the PIC32 and then the data is tagged with that time counting onwards.

Comments

  • wjcroftwjcroft Mount Shasta, CA

    Alwyn, hi.

    Timestamps you see in the GUI csv file, are generated by the GUI (or Hub) when the packets are received by the app on the laptop. Hence they contain a variable amount of delay factor caused by OS buffering, scheduling, etc. If you need accurate synchronization / triggering information, use "external triggering".

    https://docs.openbci.com/docs/02Cyton/CytonExternal

    Regards, William

  • BioPotentialBioPotential

    Hi William good to note that, I believe that packets are sent to the PC via Bluetooth radio, I have a model where the dongle is based on RFD22301, I guess the data would be sent a packets and also arrive at the PC in packets. So would the PC assing all the data in the packet with the current time?

  • wjcroftwjcroft Mount Shasta, CA
    edited February 2020

    @BioPotential said:
    ... I guess the data would be sent a packets and also arrive at the PC in packets. So would the PC assing [accessing?] all the data in the packet with the current time?

    I'm not quite understanding your question. The RFduino on the mainboard sends one packet at a time, 250 times a second. The RFduino on the dongle receives these individually and forwards them to the consuming app.

    The time the packet arrives at the dongle is NOT the time shown in the timestamp. The timestamp shows the time the data arrived at the app. Which includes various buffering, scheduling, OS, usb, delays.

    You can use the timestamp for a general idea of the time, but it's not precise and can be quite variable depending on other system delays. It will certainly be accurate within a few seconds, but no farther.

  • BioPotentialBioPotential

    Thanks for the clarifications!

  • retiututretiutut Louisiana, USA

    Hey @BioPotential, while testing timestamps with Brainflow+GUI, I noticed that applying the FTDI buffer fix increased the timestamp accuracy! Not sure if this is the case for current NodeJS drivers + GUI, but it may be worth looking into, especially if you are on Windows. It's an easy fix there.

    https://docs.openbci.com/docs/10Troubleshooting/OpenBCI_on_Windows

  • BioPotentialBioPotential

    @retiutut, thanks for the update, that information will surely help.

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