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XDR display must be connected before ThunderBay

(@mikehblue)
Active Member

Hello, I have noticed a particular annoying phenomena. I noticed I have to connect my XDR display first to my Mac, before connecting my thunder bay 8. If I connect in the opposite order then my display will not get video. I am connecting both to the same side of my Mac (presumably the same thunderbolt bus).

I also have a CalDigit TS4 dock, and when I connect my dock to my Mac with both my XDR display and thunderbay8 already connected to my dock, same thing (thunderbay mounts but my XDR display video never comes up). Likewise if I connect my dock first, then plug in my XDR display to the dock before the thunder bay, then everything will work.

 

Any advise?

 

  • 16" 2019 MacBook Pro MacOS 12.4
  • Apple Pro Display XDR
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Topic starter Posted : 21/06/2022 1:41 pm
(@softraid-support)
Member Admin

Problem is I don't have access to a XDR. I have asked for this to be tested on a Studio Display, should also show the problem.

This post was modified 1 week ago by SoftRAID Support
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Posted : 21/06/2022 4:57 pm
(@mikehblue)
Active Member

The XDR display works plugged into the back of the thunder bay 8. I can use both plugged into my Mac only as long as I always connect the xdd display first, same tru for the cal digit ts4 dock...

 

Do you have any other ideas I can research? Is there such a thing as setting priority for thunderbolt devices or an software-connection order?

 

Thanks,

-Mike

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Topic starter Posted : 22/06/2022 12:27 pm
(@softraid-support)
Member Admin

@mikehblue 

note: https://support.apple.com/en-us/HT210437

the XDR should be direct connected to the Mac.

if you restart, with everything connected, is that when you noticed the display not working correctly?
To fix it, you need to unplug everything, then connect the XDR first, then the Thunderbays?
What if you shut down and restart? Does the XDR appear after a cold restart?

If you connect them on different buses, does this happen? (i.e, try connecting the Thunderbay from the other side)
(remember on intel, each Bus has two "ports",but they are actually on the same bus)

This post was modified 1 week ago by SoftRAID Support
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Posted : 22/06/2022 12:41 pm
(@softraid-support)
Member Admin

@mikehblue 

In discussing this with colleagues, this seems to be a issue with how bandwidth is allocated to the XDR. if the Thunderbay is connected first, the allocated bandwidth prevents the XDR from getting what it needs.

One of our engineers suggested:
Likely the TB allocation occurs when the first device of the chain is plugged in. If you add a device to the chain that requires something special like the XDR display, you may run into an issue. This is just a guess, but likely probable. You noticed that the display works when it is plugged in before the entire chain is connected to the host.

 

This means there is unlikely a fix to this.

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Posted : 22/06/2022 1:28 pm
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