Hi folks,
TL;DR, I’m trying to wrap my head around how MST-enabled docks work. To my knowledge, they’re fully fledged computers, so it would make sense it’s using a completely different protocol than the DisplayPort tunneled through USB-4 (which AMD has gimped to 1 instead of 2). which would mean that the FW13-Ryzen should be able to utilize the numbers of displays an MST-enabled dock offers.
I keep trying to find information on this. I find the wiki-stickied post on the framework forum is not really helping since they bungle both Intel and AMD framework toghether in the support matrix…
Anyway,
Here’s what I figured out so far. Everything below is only about the two upper USB4-ports, since the limitations of the other ports are well documented.
- No MST controller on dock?
- Needs display port through USB4.
- AMD gimped the usb4 controller and only supports ONE attached display per USB-C ports
- On Intel-based laptop, it would be supporting two displays on non-MST docks, since Intel TB4 has two display channels in a single connection.
- MST Controller on dock?
- With intel, does it multiplex each of the two channels or it’s a different beast?
- Macbooks don’t support MST, stuck with SST, so with certain docks that supports MST, that cuts the numbers of external displays down to half + 1 mirrored.
- WHAT ABOUT FRAMEWORK??? Is it like a MBP? Is MST a completely different beast?
When you have a TB4 dock that supports 4 displays WITH MST, like these insanely expensive Satechi ones, does it matter if it’s AMD or not?
What I’m trying to wrap my head around is, does MST needs the two DisplayPort channels to output on 4 different monitors, or it’s negotiating a completely different protocol to tunnel the pixels to the attached displays?
I currently got a triple screen configuration. I love it. However, it’s going through an external GPU and I’d like to get rid of it. It’s an ‘old’ vega64 that I could repurpose for other things, would make my desk cleaner, etc. OTOH, I love the idea of having just one cable plugged in to my laptop.
So, would a dock with MST, that says is supporting TB4 and 4 displays, works with more than two displays on the Framework Ryzen 13?
1 DP Connection per USB4 port. To stay in line with the other situations.
No, just similar to USB hubs, can redirect parts of the incoming data to specific outputs. Typically, the host’s GPU is more limited in amount of MST-streams through a single DP connection or total number of displays than most MST-Hubs are.
One or both of the DP connections through USB4/TB will run in MST-mode, which will then be split by MST-Hubs. Both DP connections remain fully separate, just like they do without MST.
MST-Hubs typically have a fallback mode for SST, where they will simply forward the exact incoming signal to each and every output. Which of the outputs monitor’s data they will pick to represent to the host, that cannot conceive of their being more than one display behind a single connection is the MST-hubs business / random.
Depends on whether that dock splits 1 DP connection into 4 with 1 MST-Hub or a topology of MST-Hubs, or whether it uses both DP tunnels, each with a 2-port MST-Hub.
Typically it is the latter, because then, Apple hosts can still use 2 outputs, as long as they are on separate DP connections. If all outputs come of a single incoming DP connection, Apple would only recognize a single display.
DP MST technically supports up to 63 separate streams wrapped into one DP connection. It does not support combining multiple DP connections. Although typical GPUs have a limit of like 4 displays total. And currently available MST-Hubs, like the very popular Synaptics VMM53xx series in HP, Lenovo and Dell TB and USB-C docks supports up to 12 streams, max. 4 on each of the 3 possible outputs.
MST-Hubs can be chained, like the Lenovo TB4 dock does it in order to split one of those 3 outputs into 2 outputs for the total of 4 outputs that would work, even on AMD USB4 hosts or even DP Alt mode only hosts.