Looks like Club 3D has finished their DisplayPort 1.4 MST hub, the CSV-7300.
StarTech has also announced one (MST14DP123DP). It looks identical to the Delock-87737.
Does the CSV-7300 use the same Synaptics VMM5330 chip as the StarTech and Delock?
What does the following statement mean? Or what should I take away from knowing that the CSV-7300 has this feature? What’s a slice? Is there a 3 or 5 slice decompression? What’s the difference?
“DSC 1.2 transport and up to 4-slice decompression”
The reason I ask, is because there is something I don’t understand about the supported combinations of resolutions. For example, as far as I know, 8K30 24bpp only requires HBR3 (non DSC). If DSC has a 3:1 compression ratio, then shouldn’t two or three of those be allowed?
The specification sheet has the following asterisk note:
“*Requirement: – Host must support DP1.4 with DSC1.2 feature”
The asterisk seems to apply to all the resolutions but this is unclear because the asterisk is in the middle of every resolution like this “3840×2160*60Hz, 24bpp”. I think you need a separate table for non DSC? But you have the table above that which should be sufficient but it neglects to show the bits per pixel and it’s missing the 8K30 option. The table with heading “DP1.4 Output Port 1, DP1.4 Output Port 2, DP1.4 Output Port 3” and showing all three combinations of connecting one or two displays is redundant if you fixup the first table and just say that displays can be connected to any output port without change in behavior.
The asterisk seems to state that the hub can’t even do a single 8K30 24bpp without DSC – even though HBR3 has enough bandwidth. Does this mean MST adds a lot of bandwidth? I know it adds some, but this seems excessive. Well, I did the calculation, assuming CVT-RB timing, an overhead of only 4.823% will make 8K30 24bpp not work. That seems reasonable. What is the actual overhead? Using CVT-RB2 timing, more than 5.9% overhead would cause 8K30 24bpp to not work.
This amount of overhead doesn’t explain why DSC only allows one 8K30 24bpp instead of two. Maybe the compression ratio is not 3:1? It doesn’t seem to be at least 2.5:1 because otherwise 8K60 24bpp would be supported. 2:1 is not enough because it only allows 4.41% overhead (using CVT-RB timing).
The tables don’t say what kind of timing is used (CVT-RB or CVT-RB2).
Does the MST hub support converting DSC to non DSC? It does not say otherwise so I assume that is true. In other words, DSC can be used on the input to allow output to more 4K60 non DSC displays than could otherwise be supported by non DSC HBR3.
I believe the MST hub can convert between different link rates and link speeds. For example, it can convert HBR3 x4 MST to dual HBR2 x4 SST to drive a dual cable DisplayPort 1.2 display like the Dell UP2715K at 5K resolution (only at 24bpp though) from a single DisplayPort 1.4 port. Or it can convert HBR2 x4 to HBR3 x2 (if you have an old DisplayPort 1.2 source and want to use a new DisplayPort 1.4 two lane adapter to its full capability).
Back to the statement in the specification sheet that says “DSC 1.2 transport and up to 4-slice decompression”. While I don’t know what a slice is, I believe that it means that the hub can transmit DSC from the GPU to a display that supports DSC, and it can decompress DSC from a GPU to a display that does not support DSC, but it cannot compress a DisplayPort signal from a GPU and and send that compression output to a DSC display. Is that correct?
Does HDCP affect the ability to decompress?