Two computers and one Studio Display?

[pkamb]

Studio Display KVM switches were discussed on the recent Accidental Tech Podcasts.

They link the amazon USB-C switch linked earlier in this thread and say it works for the Studio Display.


https://atp.fm/478 (43:22)

• USB-C “KVM” (via abcd)

https://atp.fm/479 (40:03)

• USB-C KVM dev boards do exist, as found by Victor Leung

 

[edanuff]

It's the Studio, but the MBP looks identical.

That's interesting. So it is switching Thunderbolt but it's only doing so at 20 G/s, so it's doing DSC. Some of the sellers of those switchboxes have claimed they do TB3 so it seems they were telling the truth. You're definitely not going to want to hang anything off of the monitor's USB-C ports but the camera and audio should work fine with that.

 

[BeatCrazy]

I can confirm that this switch (which I assume is the same as all the other branded versions) DOES work with these cables (3 ft). Switching between a Mac Studio Max and a 2019 16" MBP connected to a Studio Display. 5K resolution, speakers, webcam all work perfectly.

The Amazon Basics cables also work when directly connected from either system to the display.

I was not expecting any of this to work given the lack of TB3 support in both the cables and the switch, but it does. I have no idea if this is using "DSC" or Displayport or whatever, but happy to run any tests/diagnostics if anyone wants more info.

Can you double-check you're getting 5K resolution? I tried a variety of USB-C cables, included three different ones rated at 10Gbps, but they all top out at 4K. Only my TB3/TB4 cables passed the real 5K. I must have tried a dozen different cables in order to reach this conclusion.

 

[cz_]

Yep -

 

[currocj]

And this is where things will fall apart if the Studio Display requires two DisplayPort signals encapsulated in a Thunderbolt 3 stream for 5K 60Hz 10bpc RGB, each driving one half of the screen at 2560×2880 (like the LG UltraFine 5K does). If this is the case, it doesn't matter if the switch supports "8K" or whatever.

The LG 5K is DisplayPort 1.2. Does anyone know if the Studio Display finally gives us 5k with DisplayPort 1.4 / HBR3 ?

 

[BeatCrazy]

Yep -

View attachment 1993391

Color me perplexed!

@joevt can you speculate on why/how a USB 3.1 Gen 2 (10Gbps) is able to pass the full 5120x2880 to the Studio display? I can't replicate, and it was my understanding that (even with DSC), you needed a 20Gbps or 40Gbps Thunderbolt cable to get 5K.

 

[edanuff]

Color me perplexed!

@joevt can you speculate on why/how a USB 3.1 Gen 2 (10Gbps) is able to pass the full 5120x2880 to the Studio display? I can't replicate, and it was my understanding that (even with DSC), you needed a 20Gbps or 40Gbps Thunderbolt cable to get 5K.

20 Gbps DSC can do 5K. As to why the switch works, it's pretty simple, the text of the switch is misleading. This was never a USB 3.1 Gen 2 switch, it was always a USB alt-mode switch. The question was whether it could switch Thunderbolt or was just switching DisplayPort over USB-C. Everyone assumed it was the latter, but it looks like it is able to switch a 20 G/s reduced form of Thunderbolt 3.

 

[BeatCrazy]

Yep -

View attachment 1993391

Sorry for the double post here, but @cz_ ^^^ That is not the correct way to determine displayed resolution, as that will remain constant regardless of the signal being sent to the Apple Studio Display.

You'll need to go into About this Mac, Displays. Please post what you see in this screen:

 

[BeatCrazy]

20 Gbps DSC can do 5K. As to why the switch works, it's pretty simple, the text of the switch is misleading. This was never a USB 3.1 Gen 2 switch, it was always a USB alt-mode switch. The question was whether it could switch Thunderbolt or was just switching DisplayPort over USB-C. Everyone assumed it was the latter, but it looks like it is able to switch a 20 G/s reduced form of Thunderbolt 3.

I still don't believe it See my post above.

 

[maverick808]

Sorry for the double post here, but @cz_ ^^^ That is not the correct way to determine displayed resolution.

You'll need to go into About this Mac, Displays: View attachment 1993415

That’s not right, what it shows in System Report is correct. It might be correct in About->Displays as well, but System Report is definitely accurate.

 

[BeatCrazy]

That’s not right, what it shows in System Report is correct. It might be correct in About->Displays as well, but System Report is definitely accurate.

System Report shows the native resolution of the display, not the input resolution.

You can see in my screenshot below, where I purposely "forced" 4K by using a 10Gbps USB-C cable (instead of Thunderbolt).

So they both can't be correct

 

[badsector]

i have a old late 2013 mbp on bootcamp and a 14" mbp m1

what's the best way to connect with this usb-c switch?

 

[cz_]

Sorry for the double post here, but @cz_ ^^^ That is not the correct way to determine displayed resolution, as that will remain constant regardless of the signal being sent to the Apple Studio Display.

You'll need to go into About this Mac, Displays. Please post what you see in this screen: View attachment 1993415

Same on both MBP and Mac Studio:

 

[BeatCrazy]

i have a old late 2013 mbp on bootcamp and a 14" mbp m1

what's the best way to connect with this usb-c switch?

No guarantees it will work at all, but you'll need one of these to at least start trying:

Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter

Effortlessly connect your Mac to a Thunderbolt 2 device with the Apple Thunderbolt 3 Adapter. Buy now at apple.com

www.apple.com

 

[badsector]

No guarantees it will work at all, but you'll need one of these to at least start trying:

Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter

Effortlessly connect your Mac to a Thunderbolt 2 device with the Apple Thunderbolt 3 Adapter. Buy now at apple.com

www.apple.com

i do have this apple tb3 to tb2 adapter. but i read somewhere it won't works

 

[joevt]

The CAC-1332 would be easier/better, as you would only have to run a single cable to the monitor, and manually switch over. But I can't find it for sale anywhere!!

There are currently no HDMI 2.0 to DisplayPort or USB-C adapters that can do greater than 4K width. It would be nice to do 5K width even if the refresh rate needs to be reduced to 39Hz.
https://insights.club-3d.com/thread/hdmi-2-1-to-usb-c-displayport-1-4-alt-mode/

Is that the Mac Studio Max or the MBP? It's definitely doing Thunderbolt video, if it was doing DisplayPort it wouldn't appear in the System Report in that section.

For Thunderbolt, you would see the display in both the Graphics/Displays section and the Thunderbolt section of System Information.app.

That's interesting. So it is switching Thunderbolt but it's only doing so at 20 G/s, so it's doing DSC. Some of the sellers of those switchboxes have claimed they do TB3 so it seems they were telling the truth. You're definitely not going to want to hang anything off of the monitor's USB-C ports but the camera and audio should work fine with that.

Thunderbolt 3 at 20 Gbps instead of 40 Gbps. Very much like Thunderbolt 2.

Yep -

Sorry for the double post here, but @cz_ ^^^ That is not the correct way to determine displayed resolution, as that will remain constant regardless of the signal being sent to the Apple Studio Display.

You'll need to go into About this Mac, Displays. Please post what you see in this screen:

That’s not right, what it shows in System Report is correct. It might be correct in About->Displays as well, but System Report is definitely accurate.

I don't think there's anywhere in macOS that you can trust to get the output resolution. Instead you should use SwitchResX, double click the current resolution, and verify the pixel clock and active pixels.

@joevt can you speculate on why/how a USB 3.1 Gen 2 (10Gbps) is able to pass the full 5120x2880 to the Studio display? I can't replicate, and it was my understanding that (even with DSC), you needed a 20Gbps or 40Gbps Thunderbolt cable to get 5K.

A 10 Gbps cable is actually a 40 Gbps cable because it has 4 lines. USB 3.1 uses only two of the lines - one for transmit and one for receive. For a Thunderbolt connection, it allows 20 Gbps in each direction (the bits are moving at slightly above 10 Gbps on the wire - 10.3125 Gbps). A DisplayPort HBR2 connection uses 5.4 Gbps for each line (21.6 Gbps) to transmit up to 17.28 Gbps of data. For Thunderbolt, DisplayPort is tunnelled as Thunderbolt without transmitting the stuffing symbols that are used to fill up the HBR2 x4 bandwidth so that reducing the bandwidth can increase the amount of bandwidth allowed for PCIe which is used to communicate with the USB controller of the display.

5K60 on the Apple Studio Display uses 936MHz pixel clock. It can be done with one of these bandwidths:

1) 11.23 Gbps = DSC@12bpp; YCbCr 4:2:0 12bpc; RGB 4bpc (8.77 Gbps remaining for USB transmit)
2) 14.98 Gbps = DSC@16bpp; YCbCr 4:2:2  8bpc;          (5.02 Gbps remaining for USB transmit)
3) 16.85 Gbps = DSC@18bpp; YCbCr 4:2:0 12bpc; RGB 6bpc (3.15 Gbps remaining for USB transmit)

Except:
- the default bpp for DSC in macOS is 12bpp (I think this can be changed to an integer value but no-one has tested it #172 . DSC may actually allow sixteenths of a bpp but testing that would require a driver patch).
- There's no such thing as 4bpc (12 bpp) or 5bpc (15 bpp) or RGB565 (16 bpp) for DisplayPort or HDMI.
- macOS doesn't support 6bpc (but Windows does for AMD and Nvidia GPUs; Intel can do 6bpc only for HDMI?). No-one has shown 6bpc on the Studio Display yet but it works on the XDR.
- The Studio Display doesn't support YCbCr 4:4:4 or 4:2:2 or 4:2:0 or no-one has tested it yet.

Display output from Thunderbolt should not greatly lower USB receive bandwidth from 9.7 Gbps.

20 Gbps DSC can do 5K. As to why the switch works, it's pretty simple, the text of the switch is misleading. This was never a USB 3.1 Gen 2 switch, it was always a USB alt-mode switch. The question was whether it could switch Thunderbolt or was just switching DisplayPort over USB-C. Everyone assumed it was the latter, but it looks like it is able to switch a 20 G/s reduced form of Thunderbolt 3.

Yup.

With a Thunderbolt 20 Gbps connection, you can still do ≈10 Gbps read (and only slightly less for write). With a DisplayPort Alt Mode connection, you would be limited to USB 2.0 speeds.

 

[cz_]

I don't think there's anywhere in macOS that you can trust to get the output resolution. Instead you should use SwitchResX, double click the current resolution, and verify the pixel clock and active pixels.

Confirmed that this shows 936.00 MHz, 5120x2880.

Except:
- the default bpp for DSC in macOS is 12bpp (I think this can be changed to an integer value but no-one has tested it #172 . DSC may actually allow sixteenths of a bpp but testing that would require a driver patch).
- There's no such thing as 4bpc (12 bpp) or 5bpc (15 bpp) or RGB565 (16 bpp) for DisplayPort or HDMI.
- macOS doesn't support 6bpc (but Windows does for AMD and Nvidia GPUs; Intel can do 6bpc only for HDMI?). No-one has shown 6bpc on the Studio Display yet but it works on the XDR.
- The Studio Display doesn't support YCbCr 4:4:4 or 4:2:2 or 4:2:0 or no-one has tested it yet.

Anything I can do to test/confirm any of this? I ran your AllRez utility on my Intel MBP, output is attached if it's of interest.

 

[joevt]

Confirmed that this shows 936.00 MHz, 5120x2880.

Yup. You have working 5K60 using DSC@12bpp.

{ 7: id:0x80002003 2560x1440@0.000Hz 0Hz (dens=2.0) pixels:5120x2880 resolution:217x222 32bpp 10bpc 3cpp rowbytes:20480 IOFlags:(Valid,Safe,Default,) flags:(Valid,Safe,Default,) depthFormat:8 encoding:--RRRRRRRRRRGGGGGGGGGGBBBBBBBBBB refreshRate.unk0.unk1:00000000.0000.00000001 };
{ DetailedTimingInformation = { V2 id:0x80002003 5120x2880@60.000Hz 180.000kHz 936.000MHz (errMHz 0,0)  h(8 32 40 +)  v(106 8 6 -)  border(h0:0 v0:0)  active:5120x2880 (not scaled) inset:0x0 flags(0°,) signal(multi aligned,) levels:1000_0400 links:2 vbext:0 vbstretch:0 vbshrink:0 encodings(RGB,) bpc(12,) colorimetry(NativeRGB,) dynamicrange(SDR,) dsc(1280x2880 12bpp) }; DisplayModeInformation = { 5120x2880@60.000Hz maxdepth:2 flags:Valid,Safe,Default, imagesize:600x330mm }; ID = 0x80002003; },
IOFBTimingRange = { V2 version:2 10…500Hz 10.000…500.000kHz 0.040…1284.000±0.000MHz sync(VRR,) levels() signal(interlaced CEA,multi aligned,) (total,active,blank,frontp,syncw,border1,border2)(charsize(h(1,2,1,1,1,1,1) v(1,2,1,1,1,1,1)) pixels(h(32768,2…32768,1…32768,1…32768,1…32768,0…0,0…0) v(32768,2…32768,1…32768,1…32768,1…32768,0…0,0…0))) links(#:0 0:0.040…1284.000 1:0.040…1284.000 MHz) encodings(RGB,444,420,) bpc(8,10,12,) colorimetry(NativeRGB,sRGB,AdobeRGB,BT601,BT709,BT2020,) dynamicrange(SDR,HDR10,DolbyNormalMode,TraditionalGammaSDR,) 0.0.0.0.0.0.0.0.0.0.0 dsc(18446744072.570Gbps?(32-bit sign extension error) slice:1x8…5184x4320 slice/line:1…4 8…12bpc 6…63bpp VBR:disabled BlockPred:?used but VBR is disabled) };

I wonder why the DisplayPort I2C failed to the Studio Display (but it worked with the built-in display). Is the display connected directly to the Mac? Maybe I need to test with displays connected by Thunderbolt.

I ran your AllRez utility on my Intel MBP, output is attached if it's of interest.

Thanks for the output. I see some things I can add/improve. I updated AllRez to make the output more compact (properties dumps no longer include fields that are output separately).

Anything I can do to test/confirm any of this?

I suppose you could try different dscTargetBPP values between 8bpp and 18bpp. IOFBTimingRange says the GPU supports DSC@6bpp but I don't know if that applies to RGB - try it to see if it works or not. The reason to test lower dscTargetBPP values is because the default 12bpp is too much for 8K60. 10bpp is needed for 8K60 HDMI 2.1 using HBR3. 8bpp is needed for 8K60 CVT-RB using HBR2. I think you just need to disconnect and reconnect the display to make the setting take effect? Otherwise you may need to restart between tests. Verify that the display is using the new dscTargetBPP by checking the output of AllRez or AGDCDiagnose.

You need Boot Camp with AMD drivers to test 6bpc and YCbCr and chroma sub sampling (4:2:2 and 4:2:0). You may need to add YCbCr and 4:2:2 and 4:2:0 manually to the EDID (using CRU) if the options don't automatically appear in the Radeon software. I expect YCbCr 4:4:4 to show weird colors and I expect 4:2:2 and 4:2:0 to have no image.
When you make the change to bpc or YCbCr/RGB or chroma sub sampling level, verify the results (and active resolution) in the Advanced Display Settings in Windows Display Settings.

 

[meltedbutter]

Wow that's perfect maybe if there's enough interest we could do a group buy if it's a quantity thing

I'm REALLY tempted to start a Kickstarter if something else doesn't show up soon. I've e-mailed them to see if they've already sold some to a reseller and if so, if they can forward me contact info. I also asked for pricing info in case I have to go the Kickstarter route.

 

[bobdard]

I've purchased this switch (which comes with a cable as well) and this additional cable.

1. The additional cable works well connecting my Mac to ASD @ 5K
2. The additional cable, connects the Mac to switch, switch to ASD @ 4K
3. The cable the switch comes with, connects the Mac to switch, switch to ASD @ 4K

In all cases, the Mac = tested with both 2019 13" MBP & 2021 MS Max, one by one. no difference.

So I'm struggling to get 5K resolution out of either cable, when used with the switch.

Any ideas?

 

[edanuff]

Confirmed that this shows 936.00 MHz, 5120x2880.

@cz_ Is the top of your switch labeled "USB-C Bidirectional Switch Data & Video & PD" or "Type C All In One Bidirectional KVM Switch"?

 

[bobdard]

I've purchased this switch (which comes with a cable as well) and this additional cable.

1. The additional cable works well connecting my Mac to ASD @ 5K
2. The additional cable, connects the Mac to switch, switch to ASD @ 4K
3. The cable the switch comes with, connects the Mac to switch, switch to ASD @ 4K

In all cases, the Mac = tested with both 2019 13" MBP & 2021 MS Max, one by one. no difference.

So I'm struggling to get 5K resolution out of either cable, when used with the switch.

Any ideas?

An update: I've purchased a serial of USB 3.1 Gen 2, TB3, TB4 cables, in different lengths. All give me the same results - 4K res in About this Mac > Displays. All of them also give the 5K res when connecting Mac directly to the ASD.

I'm guessing there is a difference between the switch I bought (available at Amazon Canada) and the one purchased by @cz_

I'll see if a friend in the US can purchase the different units to try out.

 

[joevt]

I've purchased this switch (which comes with a cable as well) and this additional cable.

1. The additional cable works well connecting my Mac to ASD @ 5K
2. The additional cable, connects the Mac to switch, switch to ASD @ 4K
3. The cable the switch comes with, connects the Mac to switch, switch to ASD @ 4K

In all cases, the Mac = tested with both 2019 13" MBP & 2021 MS Max, one by one. no difference.

So I'm struggling to get 5K resolution out of either cable, when used with the switch.

Any ideas?

Show us AGDCDiagnose for the 2019" MBP.

 

[edanuff]

Show us AGDCDiagnose for the 2019" MBP.

I'm going to get one of these switches. How should I test before and after on an M1 Mac to see what the pixel clock looks like?

 

[edanuff]

Ok, I received one of these ConnBull switches and tried it out. This one is labeled "USB-C Bidirectional Switch Data & Video & PD" and not "Type C All In One Bidirectional KVM Switch". Part number is A0206. SKU is A0206-D0103*2-3. This one *does not* switch Thunderbolt but it will switch DisplayPort. Tried with Mac Studio and PC 3080 Ti using the Bellkin cable. Everything works fine at 5K@60Hz with the PC connecting with the Belkin cable and the Mac Studio using a Cable Matters 10 Gbps Gen 2 USB C to USB C Cable 3.3 ft. The Mac is identifying and driving the monitor at 5K but not appearing as Thunderbolt. Neither a Cable Matters 40Gbps Active Thunderbolt 4 Cable 6.6 ft nor the Apple Thunderbolt cable 1m from the Studio Display box nor a Corning Optical TB3 cable work with the switch. Would be great if @cz_ could post what if theirs is the same unit or whether they received a "Type C All In One Bidirectional KVM Switch".