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CSV-1580 Thunderbolt 4 Portable 5-in-1 Hub connecting 3 displays

Updated on 23-05-2022 in Docking Station
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3 on 18-02-2022

In one of the product pictures at
https://www.club-3d.com/en/detail/2542/thunderbolt_4_portable_5_in_1_hub_with_smart_power/
it shows how to connect 3 displays (one 8K30 and two 4K60) using 3 Thunderbolt 4 hubs.

My question is, how was this tested? As far as I know, there are no Thunderbolt host controllers that support more than 2 DisplayPort connections.

How to get 3 DisplayPort connections on a single Thunderbolt cable? I suppose one way might be to use an eGPU that has DisplayPort inputs from their GPU (such as the Sonnet eGPU Breakaway Puck 5500XT/5700). In this way, two DisplayPort connections could come from the host’s GPU and two DisplayPort connections could come from the GPU. I don’t know if all 4 DisplayPort connections would be allowed down the downstream Thunderbolt port of the eGPU – for example, if you connect four HBR (8.64 Gbps) displays. I don’t know if these eGPUs work with PCs.

If there was a host that supported 3 DisplayPort connections out a single Thunderbolt port, then it would only require two Thunderbolt hubs to connect three displays since each Thunderbolt hub can connect two displays.

What about bandwidth? Two 4K60 displays normally take 16Gbps for 30bpp or 12.8 Gbps for 24bpp each and an 8K30 display normally takes 24.7 Gbps for 24bpp. Since Thunderbolt only has 40Gbps, there’s not enough bandwidth for two 4K60 and one 8K30. Therefore, we need chroma sub sampling or DSC. Either method can reduce the bpp down to 12bpp (DSC might be able to do 8bpp). In that case the 8K30 would require 12.4 Gbps and the 4K60 displays would require 6.4 Gbps each.

What if you don’t have a display that supports DSC or 4:2:0 chroma subsampling? A DisplayPort 1.4 MST hub can be used to convert a DisplayPort with DSC signal to an uncompressed DisplayPort signal. These can be connected to the Thunderbolt hubs. For example, an MST hub can convert HBR2 with DSC to HBR3 without DSC. Of course, you need a GPU that supports DSC.

Is Thunderbolt smart enough to have 3 DisplayPort connections on the same cable? Probably not. You would need a method to set the link rate of each DisplayPort device. Apple has code in its drivers to force two HBR3 links for an XDR display even though that would normally exceed Thunderbolt bandwidth (it works because the XDR doesn’t require all the bandwidth of each HBR3 link). For our purposes, we need two HBR links for the 4K60 displays and one HBR2 link for the 8K30 display. Without special software to do that, we might be able to shuffle some HBR and HBR2 displays to divide up the bandwidth the way we want.

What’s the alternative if there is no way to get 3 separate DisplayPort links? For PCs, MST hubs can allow connecting multiple displays from a single DisplayPort link. For this setup, you need one Thunderbolt 4 hub and one or two MST hubs. 12.4 + 6.4 + 6.4 = 25.2 Gbps which is less than the max (25.92 Gbps) for a HBR3 link so maybe one MST hub is sufficient but MST might have some overhead that I’m not accounting for. Therefore, we’ll use two HBR2 links (17.28 Gbps), connect the two 4K60 displays to one MST hub, and the 8K30 display to another MST hub (if the 8K30 display doesn’t support DSC). You might need to use the display shuffling method to force each MST hub’s upstream DisplayPort connection to HBR2. Remember, the MST hubs must support DisplayPort 1.4 and DSC – just like the GPU.

A simpler method (but less performant since it doesn’t use the GPU directly) is to use DisplayLink adapters for the 4K displays. DisplayLink gets compressed video from USB 3.0. Each display takes between 1 Gbps and 4 Gbps (I haven’t seen benchmarks).

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MST1407 0 on 22-02-2022

Hi Joevt, based on the specifications of Thunderbolt4 it will support 2x4k60Hz or 1x8K30Hz. Club3D tested this setup with Intel NUC with Iris XE and with a similar Lenovo Iris XE Thunderbolt 4 based solution. The actual image should show one or the other and not make it look like one and the other. While typing this – this image will be adjust to correct this. 

There are a few points you mentioned in regards to DSC, while we have not been able to detect a DSC 1.1 solution that can convert HBR 2 to HBR 3 without DSC, theoretically this is correct. We have only been able to detect DSC 1.2 compression on latest Nvidia RTX2X series where Decoding takes place. However as you know for DSC to work, Decode, Encode and Bypass needs to take place. We think that Iris xE should be able to do this as we have tested it with the CAC-1085/CAC-1586 adapters but not able to find DSC working on the Thunderbolt 4 hub. with the integrated chip. 

the CSV-1580 is more a hub than a dock – note that some streams go to the video output support x2 and the rest is going for data. 

Suggestion when you want to have three displays will be best to go for DisplayLink solution. Adding an MST to the Thunderbolt 4Hub does not work. its still limited to two displays. DisplayLink solution that adds the third display from the source that support HBR3 would be the best scenario. This is a work in progress within Club3D 

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joevt 0 on 27-02-2022

Thanks for the clarification regarding the image.

About DSC, I’m not sure what the distinction is between 1.1 and 1.2 or what in my discussion  the version number of DSC would affect or applies to. There’s a list of some differences at
https://vesa.org/vesa-display-compression-codecs/
but as far as I know, most solutions that support DSC are using 1.2 for DisplayPort. I would be interested to know of an example of DSC 1.1.

Regarding MST hub connected to Thunderbolt 4 Hub (CSV-1580 or anything else that uses Goshen Ridge) it seems strange to me that the MST hub wouldn’t work to allow multiple displays. Instead of Iris xE, maybe a 690 motherboard with Maple Ridge Thunderbolt 4 add-in card (or built-in Maple Ridge with DisplayPort input for Radeon Navi or Nvidia RTX) might have different behavior? The HP Thunderbolt Dock G2 is an example of a Thunderbolt dock with an MST hub connected to it (internally). It’s Thunderbolt 3 (Titan Ridge) but I would expect Thunderbolt 4 to be just as capable. I was able to connect 3 4K60 HBR2 displays to that. The total output bandwidth exceeds HBR3 so DSC is working.

Regarding using an MST hub to convert HBR2 with DSC to HBR3 without DSC, maybe a better example to illustrate MST hub format conversion is with a two lane USB-C adapter or dock that uses MST to convert two lanes to four lanes. For example, the Apple USB-C Digital AV Multiport Adapter (two lanes of DisplayPort since the other two SuperSpeed lanes are used for USB 3.0) which also supports DSC. Another example is the CalDigit SOHO which contains a two port MST hub. The CAC-1510 or CAC-1010 requires 4 lanes of HBR to do 1440p so two HBR2 or HBR3 lanes from a USB-C dock (that supports USB 3.x) will only allow 720p unless a MST hub is used to convert the two lanes to four lanes of HBR.

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Hanna 0 on 23-05-2022

This is very interested!

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