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Re: [Paparazzi-devel] How to Synchronizing the two Tiny boards?

From: Martin Mueller
Subject: Re: [Paparazzi-devel] How to Synchronizing the two Tiny boards?
Date: Fri, 26 Oct 2012 18:04:45 +0200 (CEST)

Hi Autumn,

> In order to synchronize all my data, I'm thinking if it's possible to first
> synchronize the two processors and

the two quarz crystals should not differ that much, not sure the synchronization
would make a big difference.

> then add time stamp to the telemetry data before it is sent to the ground
> station;

This would be possible but requires a rewrite of a lot of message handling code.
There is some reserved space in the "Messages Format New"?

> or add time stamp to the data gathered from the Tiny board before store it in
> the SD card?

Not sure what your setup looks like exactly. Is the TWOG listening to the Tiny
telemetry UART stream (the TWOG will add a timestamp then) or is the TWOG only
recording your extra sensor data?

> Or do you have any other suggestion for this synchronization?

The telemetry link adds jitter if not time stamped on board and there is the
risk of data loss. That makes the on-board logger the better choice.


> ________________________________________
> From: address@hidden
> address@hidden on behalf of Martin
> Mueller address@hidden
> Sent: Friday, October 26, 2012 5:30 PM
> To: address@hidden
> Subject: Re: [Paparazzi-devel] How to Synchronizing the two Tiny boards?
> Hi Autumn,
> > My name is Autumn and I'm working on a system that uses paparazzi on a Tiny
> > v2.11 board (with LPC2148 as the main processor). I added a TWOG in addition
> > to the main autopilot Tiny to take data from some sensor and log them to a
> > SD
> > card. However, the data that is logged in the SD card and the data sent back
> > via telemetry has non-matching time stamps. I wonder if I can synchronize
> > the
> > two processors by configure the TWOG to use external clock and physically
> > connect the clock pin from Tiny to the TWOG.
> the on-board TWOG log data is synchronized to the TWOGs 12MHz Quarz and starts
> when the TWOG is booted. The timestamp is added to each messsage by the TWOG
> as
> it is written to SD card.
> The log file that is recorded in the ground station is started when the ground
> software is executed. The timestamp is generated in the laptop as the message
> is
> received. There will be some jitter caused by the radio link (retries, random
> tx
> delay).
> > Have anybody ever met problems on asynchronized data from two processors or
> > between telemetry data and data stored on board?
> The Tiny does not generate any timestamp in your setup. It is the TWOG and the
> laptop.
> Martin
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