Full-size DisplayPort does get bandwidth priority if there isn't enough bandwidth for everything that's attached, but that would only be an issue when connecting more than 2x 4K @ 60 Hz displays, for example, not 3x 1080p -- in fact even if the XPS13 9365 only had a one rather than two GPU outputs wired to its Thunderbolt 3 output (which I don't believe is the case), even that would still be enough bandwidth to run 4x 1080p displays, though you'd still be limited to 3 because of the GPU. The fact that in some cases you're being limited to a external display makes no sense, and I haven't seen that reported before. TB16 drivers also wouldn't even come into play here since video isn't carried as USB traffic. The only elements that would matter would be the BIOS, Thunderbolt firmware (on the system), Thunderbolt software, and GPU drivers. If you haven't already, perhaps try going to support.dell.com and selecting your system using "Choose a product", NOT by entering your Service Tag, and see whether there are any such updates that might not be appearing in Dell Command | Update. If that doesn't fix it, any chance you have even temporary access to another Thunderbolt-equipped system or another TB16 to isolate variables?
Thanks for the feedback. Agreed that there’s no logical reason this shouldn’t work. It’s a relatively simple, lo-res setup. There was a newer video driver (a few ticks up on the minor version number) so I installed but unfortunately no change in behavior.
I suspect that the built-in display being active when either DP or VGA is connected may be the best indicator of a problem. As I said, I’m plugging/re-plugging video connections on the TB16 with the lid closed and both rebooting via Windows and power cycling the TB16. The built-in should never be active.
I think I’m all out of areas to check and permutations to try so I'll actively source a second TB16 to test.
The system can support up to 3 displays at a time, including a configuration involving 2 external displays plus the built-in panel -- so if you've only got one external display connected, it shouldn't matter whether the built-in panel is connected because the GPU would be happy either way. One thing you could try if you haven't already would be to have the Windows Display Settings interface open while you connect and disconnect displays. See if it even detects the new displays when you attach them. If so, you might have to manually switch the built-in panel to off in order to light up another one.
jphughan
9 Legend
•
14K Posts
0
September 25th, 2017 07:00
Full-size DisplayPort does get bandwidth priority if there isn't enough bandwidth for everything that's attached, but that would only be an issue when connecting more than 2x 4K @ 60 Hz displays, for example, not 3x 1080p -- in fact even if the XPS13 9365 only had a one rather than two GPU outputs wired to its Thunderbolt 3 output (which I don't believe is the case), even that would still be enough bandwidth to run 4x 1080p displays, though you'd still be limited to 3 because of the GPU. The fact that in some cases you're being limited to a external display makes no sense, and I haven't seen that reported before. TB16 drivers also wouldn't even come into play here since video isn't carried as USB traffic. The only elements that would matter would be the BIOS, Thunderbolt firmware (on the system), Thunderbolt software, and GPU drivers. If you haven't already, perhaps try going to support.dell.com and selecting your system using "Choose a product", NOT by entering your Service Tag, and see whether there are any such updates that might not be appearing in Dell Command | Update. If that doesn't fix it, any chance you have even temporary access to another Thunderbolt-equipped system or another TB16 to isolate variables?
nmusgrove
2 Posts
0
September 25th, 2017 11:00
Thanks for the feedback. Agreed that there’s no logical reason this shouldn’t work. It’s a relatively simple, lo-res setup. There was a newer video driver (a few ticks up on the minor version number) so I installed but unfortunately no change in behavior.
I suspect that the built-in display being active when either DP or VGA is connected may be the best indicator of a problem. As I said, I’m plugging/re-plugging video connections on the TB16 with the lid closed and both rebooting via Windows and power cycling the TB16. The built-in should never be active.
I think I’m all out of areas to check and permutations to try so I'll actively source a second TB16 to test.
jphughan
9 Legend
•
14K Posts
0
September 25th, 2017 12:00
The system can support up to 3 displays at a time, including a configuration involving 2 external displays plus the built-in panel -- so if you've only got one external display connected, it shouldn't matter whether the built-in panel is connected because the GPU would be happy either way. One thing you could try if you haven't already would be to have the Windows Display Settings interface open while you connect and disconnect displays. See if it even detects the new displays when you attach them. If so, you might have to manually switch the built-in panel to off in order to light up another one.