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gadgetPool.de :: View topic - Issues with SEATALK and NMEA on Autohelm ST-50
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Issues with SEATALK and NMEA on Autohelm ST-50

 
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lukabirsa
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Joined: Jul 23, 2012
Posts: 4

PostPosted: Mon Jul 23, 2012 12:34 pm    Post subject: Issues with SEATALK and NMEA on Autohelm ST-50 Reply with quote

I'm sorry for the lengthy explanation, it's only here to provide you with some background. If you wish jump down to see the actual problem:

We have built an application which implements various instruments in software and displays them on our custom handheld devices. (see picture here: https://twitter.com/visionect/status/220439911390642176/photo/1 ) - the upper row of displays are of our own production (eInk based, waterproof, very long autonomy).

We have a central PC server (an embedded PC suitable for use on a boat), which takes care of all processing and interconnection to various devices. We try to support SEATALK and NMEA0183 based devices and have currently implemented AIRMAR DST transducer and AIRMAR weather station (we support the required NMEA statements) (both via simple USB-NMEA bridges) and some SEATALK head units and autopilot via gadgetpool SEATALK link. We are capable of viewing the data from the sensors as well as controlling the autopilot.

We also built a PC based multiplexer which enables us to forward statements from one USB port to the other (and filter and/or modify them in the transit).

////////////////////////OUR PROBLEM:

Our communication chain looks like this:

- USB port 1 - simple RS232 - DST sensor
- USB port 2 - simple RS232 - Weather station with GPS
- USB port 3 - Gadgetpool SEATALK link, which has the following devices on the bus: Type 100 Autopilot, ST30 Bidata, ST7000 Autopilot Head, ST50 Wind instrument.
- PC based multiplexor which forwards the statments from the weather station to the SEATALK bus

Now, as long as we do not connect the ST50 windinstrument to the SEATALK bus, everything works as intended. If we disconnect the autopilot and leave the Bidata and Wind on it, everything works as well (ie. we get depth and wind readings on the head instruments). As soon as we connect all together, we get some serious problems on SEATALK. Wind stops responding and displaying the wind readings and autopilot response is bad. We first thought we have a faulty ST50 wind, but we replaced it and for some time it worked better (as long as we were in the lab.). When we mounted it on the boat the performance slowly deteriorated.

Now we do not know if there could be some issue with the SEATALK bus being flodded by messages (since the wind gets lots more readings when it is outside as the wind conditions change) or is there some trick with SEATALK that we forgot about.

Any help would be very beneficial, especially if somebody could explain typical gotchas that we might have when interfacing with SEATALK that we might have missed.

Thanks!


Last edited by lukabirsa on Mon Jul 23, 2012 8:46 pm; edited 1 time in total
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FWallenwein
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Joined: Mar 26, 2006
Posts: 419
Location: Mannheim / Germany

PostPosted: Mon Jul 23, 2012 6:34 pm    Post subject: Reply with quote

Hi lukabirsa,

well - I don't have THE solution on hand. But lets try to find out what's going on.

First of all - you link to the picture does not work any more.
It says "This page does not exist any more".

To find out what's going on - is there any way, that you could log the data coming and going to USB port 3 ?

I guess it would help a lot, to see what's going on on the USB port 3 and how fast data come in and go out.

If you have a way to log the data, maybe we could - in a second step - enable the SeaTalk Link function to show every Seatalk datagram on the bus. ( $SNBSE,0,1 ). Maybe this helps to find flooding or other problems.

Best regards
Frank
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lukabirsa
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Joined: Jul 23, 2012
Posts: 4

PostPosted: Mon Jul 23, 2012 8:48 pm    Post subject: Reply with quote

FWallenwein wrote:
Hi lukabirsa,

well - I don't have THE solution on hand. But lets try to find out what's going on.

First of all - you link to the picture does not work any more.
It says "This page does not exist any more".

To find out what's going on - is there any way, that you could log the data coming and going to USB port 3 ?

I guess it would help a lot, to see what's going on on the USB port 3 and how fast data come in and go out.

If you have a way to log the data, maybe we could - in a second step - enable the SeaTalk Link function to show every Seatalk datagram on the bus. ( $SNBSE,0,1 ). Maybe this helps to find flooding or other problems.

Best regards
Frank


I fixed the link and I'll to provide the logs. Thanks for the help.
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lukabirsa
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Joined: Jul 23, 2012
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PostPosted: Fri Jul 27, 2012 10:26 am    Post subject: Reply with quote

First a link to some pictures of the yesterdays testing: http://web.stagram.com/p/243892031901227181_195655341

Secondly - regarding the results.

I monitored the SEATALK bus via gpool converter and the pattern was this (keep in mind that gpool converter feeds NMEA data from sensors all trough the tests to the SEATALK bus):

Scenario 1: I could connect gpool converter with both type100 and st7000 head display and control the autopilot with the st7000 or with our device via GPOOL converter. In this case I could clearly see that we get all the activity from the SEATALK bus (even values for the backlight setting from ST7000 get transmitted).

Scenario 2: I could connect two wind instruments and bidata (slave or master, responding with values of the analog sensors) and I could clearly see that the wind instruments work and that I get all the activity from the SEATALK bus (backlight settings, analog readings from bidata).

Scenario 3: I could connect all instruments together on the bus and disconnect the GPOOL converter and I can see that the instruments work (since there is no wind data to display I tested this with changing the backlight setting which modifies the backlight on all the devices on the SEATALK bus).

Scenario 4: I could connect all instruments togeter and connect the GPOOL converter, but just keep it under power on the USB and the system performs the same as in Scenario 3.

Scenario 5: I connected the GPOOL converter (forwarding NMEA), type 100 and/or st7000 and as soon as I add the wind instrument (one or two), there is an apparent breakdown in the SEATALK communication. Wind instruments do not get the sensor data from GPOOL and the GPOOL converter doesn't hear the backlight setting anymore (other devices on the bus don't hear it as well).

I can see the following possibilities for the error:
1. The SEATALK instrumentation is old. One of the devices on the bus influences the power levels and deteriorates the communication.
2. GPOOL converter is misconfigured and adding to many devices adds some kind of collisions between the messages?
3. There is something wrong in the way we talk with GPOOL?
4. There is a bug in the GPOOL.

We will be doing more testing over the weekend and I can run a test according to your suggestions to figure out what is happening.

Additional questions:

Does anyone know what is the maximum lenght of SEATALK bus and what is the maximum number of devices on the bus? How fast do you get collisions on the bus and how does GPOOL converter handle collision avoidance / collisions?
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peterh
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Joined: May 17, 2012
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PostPosted: Sat Jul 28, 2012 8:34 pm    Post subject: nice displays Reply with quote

Are you placing all messages on a single seatalk bus ? It's limited to 4800 baud and has a collision protocol that is not very advanced.

If you use seatalk between your displays and controlling computer ONLY there
is nothing that prevents you from speeding up the bus ( or using another media that has inherent better speed, ethernet comes to my mind, POE might be a solution for "single wire connection" )
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lukabirsa
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Joined: Jul 23, 2012
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PostPosted: Mon Jul 30, 2012 8:10 am    Post subject: Reply with quote

The amount of messages is filtered, but yes, we do post a lot of messages on the Seatalk bus - this is to support legacy systems with old seatalk instruments (such as the wind and autopilot head units).
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