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INDI Library v1.8.1 Released (09 Sep 2019)

Monthly maintenance release INDI v1.8.1

Alignment starts before mount is finished slewing

1 month 4 days ago 1 month 4 days ago by Ihoujin.
Ihoujin
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Alignment starts before mount is finished slewing #45516
Maybe it is reporting a trigger signal, for lack of a better term, for each axis, one for RA, and another for DEC?

INDI/KStars on Raspberry Pi 4, 4gb
Raspbian Buster with AstroPi3 script configuration
Skywatcher HEQ5 Pro Mount
Canon 600D Camera
Orion SSAG/ASI120mm @280mm Guide Scope
PHD2
Adafruit Motor Hat shield
Adafruit GPS Module
Generic Bluetooth Joystick.
Startech 7 port powered USB Hub.

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4 weeks 1 day ago
mpfjr
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Alignment starts before mount is finished slewing #45722
Just poking.
Any further clues, hints or ideas on going forward fixing this issue?

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3 weeks 3 days ago
sterne-jaeger
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Alignment starts before mount is finished slewing #45897
Still under investigation, since it is not that easy to reproduce with Simulators. Meanwhile the best explanation I see is, that this is a concurrency issue where a slew command overtakes a sync command. It looks like a sync happens while the mount already has started to slew.

You could reproduce a similar situation using the model builder of the align module:
  1. Create a set of alignment points with the mount model tool
  2. Start the mount model routine and let the first position being resolved.
  3. Wait until the mount slews to the second position.
  4. While slewing, use the INDI dialog and sync the mount to the first position.
  5. Observe, that capturing immediately starts although the mount is still slewing

What I could not explain right now is, why the sync command is overtaken by a slew.

- Wolfgang

TSA-120 + FSQ-85 + GSO 150/750 | Avalon Linear + M-zero | Moravian G2-8300 + ASI 1600mm pro + ASI 294mc pro | KStars/INDI on Raspberry Pi 4 with Raspbian 10
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5 hours 8 minutes ago
sterne-jaeger
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Alignment starts before mount is finished slewing #46811
Hi folks,
there is a fix in the latest KStars builds that should hopefully fix this behavior. If you can compile from sources, please checkout the latest version and build it. I think it will make it into V 3.3.9 for all of you who do not compile on your own.

Meanwhile I am quite sure that it is a concurrency issue on mount level. My Avalon shows this behavior and I would not be surprised if there are many mounts out there that behave similar. There are two things that happen in parallel:
  1. KStars sends a SLEW command to the mount.
  2. The INDI driver checks the mount status (frequency defined by the polling interval in the driver's options)

If the driver status check happens very fast after the SLEW command has been sent, the mount still reports to be tracking although the slew command is already on it's way inside the mount's firmware.

KStars obtains a BUSY response directly from issuing the SLEW command (meaning that the mount is slewing) and directly afterwards it obtains a "OK" status (meaning that the mount is tracking). The latter one is created by the periodical status check. KStars itself thinks that the slew has finished although it has not started yet. And with the next check it detects that the mount is slewing again, but this was not captured in the old KStars version. That's what causes the star trails.

With the current fix, the alignment recognizes when the mount is slewing during capturing and restarts capturing as soon as the slew has terminated. So you will see the messages about a slew detected, but in all my tests it looks like the restart is working fine.

It would be great if you could test this fix and give some feedback here.

Since I can reproduce the problem with my own mount, I can continue working on it, since the solution is OK, but far from elegant...

Cheers
Wolfgang

TSA-120 + FSQ-85 + GSO 150/750 | Avalon Linear + M-zero | Moravian G2-8300 + ASI 1600mm pro + ASI 294mc pro | KStars/INDI on Raspberry Pi 4 with Raspbian 10

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