Problem controlling monitors independently using DP1.2 daisy chaining

jbirch · 05-31-2016, 07:47 PM

Hi, I am using the new Humanscale M/Connect and I have displaylink 7.9.1488 currently installed. My Surface Pro 3 has 2 X Dell U2414Hb connected to it using DP1.2 in daisy chain mode. The 3 monitors are recognized as separate monitors when connected directly to the Surface Pro. As soon as I connect the laptop to the M/Connect and use displaylink it only recognizes the 2 Dell monitors as a single monitor. The 3rd monitor has a picture but it is a mirror of the 2nd monitor. I have tried this on multiple devices using Win 7 and Win 10 with the latest firmware and get the same result every time. I have attached the appropriate logs from the Surface Pro 3 for reference. Any help is much appreciated since we need to resolve this before rolling this out to the rest of our user community.

AlbanRampon · 06-02-2016, 11:49 AM

Hello,
DisplayPort daisy chaining requires Multi-Stream Transport (MST) which is not supported by the DisplayPort transmitter, chips or firmware, used by Humanscale in their product.

The user guide page 15 mentions their dock is DisplayPort 1.2.
MST was introduced in DisplayPort 1.3 but is not supported by all devices doing DP 1.3.

This is not a driver only limitation but a hardware one.
I am sorry but DP MST will never be possible with this product.

Kind regards,
Alban

jbirch · 06-02-2016, 01:04 PM

I hate to disagree but MST was introduced in displayport 1.2 per the post on Wikipedia that you sent me -

DisplayPort version 1.2 was approved on 22 December 2009. The most significant improvement of the new version is the doubling of the effective bandwidth to 17.28 Gbit/s in High Bit Rate 2 (HBR2) mode, which allows increased resolutions, higher refresh rates, and greater color depth. Other improvements include multiple independent video streams (daisy-chain connection with multiple monitors) called Multi-Stream Transport.

The two Dell monitors have DP1.2, the Surface Pro 3 has DP1.2 and using them directly without using the M/Connect or DisplayLink they work just fine. I am investigating with Humanscale at the same time in regards to the hardware which it might still be but it should work using DP1.2 per their hardware specs.

AlbanRampon · 06-02-2016, 01:30 PM

Thank you for the information.

The DisplayLink chip connected to your computer at the time you took the log is a DL3900.
That chip does not DisplayPort itself but use an external transmitter.

I was wrong on when MST was introduced, but our chip still won't send an MST as we support DisplayPort 1.1 max. I doubt the DP transmitter does MST.
"Dual Mode" in the guide should mean you can use a passive adapter to get HDMI. I think the note in the right column refers to the maximum resolution available on the dock. You can use two outputs simultaneously (DP+another), but the maximum resolution on the DP output will drop because of the maximum pixel clock the chip can manage

DisplayLink does not design or manufacture end products, we are a semiconductor company.
I recommend you contact Humanscale for clarification on what they designed their product to do.

Kind regards,
Alban

jbirch · 06-02-2016, 01:56 PM

Thank you very much Alban for the information. Knowing the chipset info for the Humanscale definitely gives me more information and seems to suggest that based on the 3900 specs it will not support DP 1.2. I will continue to follow up with Humanscale to get confirmation.

Thanks again for the quick response.

06-02-2016, 11:49 AM	#2
AlbanRampon Senior Member Join Date: Sep 2015 Location: Cambridge, UK Posts: 1,678	Hello, DisplayPort daisy chaining requires Multi-Stream Transport (MST) which is not supported by the DisplayPort transmitter, chips or firmware, used by Humanscale in their product. The user guide page 15 mentions their dock is DisplayPort 1.2. MST was introduced in DisplayPort 1.3 but is not supported by all devices doing DP 1.3. This is not a driver only limitation but a hardware one. I am sorry but DP MST will never be possible with this product. Kind regards, Alban __________________ Alban Rampon Senior product manager, universal docking stations and accessories "DisplayLink is proud to be a Synaptics brand." Where to download the latest DisplayLink drivers How to clean up a corrupted installation How to report issues to DisplayLink for a speedy resolution

06-02-2016, 01:30 PM	#4
AlbanRampon Senior Member Join Date: Sep 2015 Location: Cambridge, UK Posts: 1,678	Thank you for the information. The DisplayLink chip connected to your computer at the time you took the log is a DL3900. That chip does not DisplayPort itself but use an external transmitter. I was wrong on when MST was introduced, but our chip still won't send an MST as we support DisplayPort 1.1 max. I doubt the DP transmitter does MST. "Dual Mode" in the guide should mean you can use a passive adapter to get HDMI. I think the note in the right column refers to the maximum resolution available on the dock. You can use two outputs simultaneously (DP+another), but the maximum resolution on the DP output will drop because of the maximum pixel clock the chip can manage DisplayLink does not design or manufacture end products, we are a semiconductor company. I recommend you contact Humanscale for clarification on what they designed their product to do. Kind regards, Alban __________________ Alban Rampon Senior product manager, universal docking stations and accessories "DisplayLink is proud to be a Synaptics brand." Where to download the latest DisplayLink drivers How to clean up a corrupted installation How to report issues to DisplayLink for a speedy resolution

06-02-2016, 01:04 PM	#3
jbirch Junior Member Join Date: May 2016 Posts: 3	I hate to disagree but MST was introduced in displayport 1.2 per the post on Wikipedia that you sent me - DisplayPort version 1.2 was approved on 22 December 2009. The most significant improvement of the new version is the doubling of the effective bandwidth to 17.28 Gbit/s in High Bit Rate 2 (HBR2) mode, which allows increased resolutions, higher refresh rates, and greater color depth. Other improvements include multiple independent video streams (daisy-chain connection with multiple monitors) called Multi-Stream Transport. The two Dell monitors have DP1.2, the Surface Pro 3 has DP1.2 and using them directly without using the M/Connect or DisplayLink they work just fine. I am investigating with Humanscale at the same time in regards to the hardware which it might still be but it should work using DP1.2 per their hardware specs.

06-02-2016, 01:56 PM	#5
jbirch Junior Member Join Date: May 2016 Posts: 3	Thank you very much Alban for the information. Knowing the chipset info for the Humanscale definitely gives me more information and seems to suggest that based on the 3900 specs it will not support DP 1.2. I will continue to follow up with Humanscale to get confirmation. Thanks again for the quick response.