Thunderbolt 4 ports on the M2 Mini

[joevt]

Anyways, what I meant was that, based on what you showed, DSC is not necessary when driving a single XDR. Hence I assumed that, even if a Mac is DSC-capable, it's only going to be using DSC with the XDR when you are driving more than one XDR on a single port (or, more generally, if you are driving an XDR plus any other monitor on that port).

Or is that not correct? Do DSC-capable Macs use DSC when driving only a single XDR on a TB port, even if that's not necessary? And if so, why?

Without DSC, the XDR requires dual HBR3 x4 over Thunderbolt using 39 Gb/s of bandwidth. That means the USB ports would be limited to 1 Gbps for writes. Read speed should still allow 4 Gbps.

OTOH, if a single XDR doesn't use DSC even on DSC-capable Macs, what about the 6k Dell?

The Dell 6K probably doesn't have a dual HBR3 mode since it has two Thunderbolt ports. Only macOS has the ability to enable dual HBR3 mode as far as I know. The mode is not enabled if there's a Thunderbolt device between the XDR and the host.

 

[theorist9]

Without DSC, the XDR requires dual HBR3 x4 over Thunderbolt using 39 Gb/s of bandwidth. That means the USB ports would be limited to 1 Gbps for writes. Read speed should still allow 4 Gbps.

Thanks, but just to make sure I'm clear on this, can you specifically confirm that this is case for DSC-capable Macs?:

Single XDR connected to single Mac TB port, run at 60 Hz, full resolution: DSC not used.

Two XDR's conncted to a single Mac TB port (using a TB dock like the CalDigit TS4), both run at 60 Hz, full resolution: DSC used for both.

One XDR plus any other display conncted to a single Mac TB port (using a TB dock like the CalDigit TS4), both run at 60 Hz, full resolution: DSC used for both.

 

[joevt]

Thanks, but just to make sure I'm clear on this, can you specifically confirm that this is case for DSC-capable Macs?:

Single XDR connected to single Mac TB port, run at 60 Hz, full resolution: DSC not used.

I'm not sure why Apple would disable DSC if the Mac were capable. Without DSC, the USB ports cannot run at a full 4 Gbps (data).

Two XDR's conncted to a single Mac TB port (using a TB dock like the CalDigit TS4), both run at 60 Hz, full resolution: DSC used for both.

Probably.

One XDR plus any other display conncted to a single Mac TB port (using a TB dock like the CalDigit TS4), both run at 60 Hz, full resolution: DSC used for both.

DSC doesn't need to be used for a display that is only 4K60. DSC only needs to be used for a display if it exceeds HBR2 x4 bandwidth.

I've received AGDCDiagnose (works on Intel Macs) for a few setups of the XDR. I would have to recheck them all to see what OS and GPU they were running on.

#======================================================================
# Some examples:

# dual HBR3
../EDID from nick82/AGDCDiagnose.txt:uint8_t EDID_APP_610_ae2e[] = {
# dual HBR2
../EDID from OCDMacGeek/AGDCDiagnose.txt:uint8_t EDID_APP_610_ae22[] = {
# HBR2 DSC
../EDID from vincek8s/5700xt_AGDCDiagnose.txt:uint8_t EDID_APP_610_ae22[] = {

#======================================================================
# All the EDIDs:


		find .. -path '*610*' -name '*ae22*'
../EDID from cmsj/EDID_APP_610_ae22_8_edid-decode.txt
../EDID from Fhed3040/EDID_APP_610_ae22_1_edid-decode.txt
../EDID from gimarbazat/EDID_APP_610_ae22_1_edid-decode.txt
../EDID from henrymyf/EDID_APP_610_ae22_1_edid-decode.txt
../EDID from Human Person/EDID_APP_610_ae22_1_edid-decode.txt
../EDID from Human Person/EDID_APP_610_ae22_3_edid-decode.txt
../EDID from Human Person/EDID_APP_610_ae22_8_edid-decode.txt
../EDID from likegadgets/EDID_APP_610_ae22_2_edid-decode.txt
../EDID from OCDMacGeek/EDID_APP_610_ae22_4_edid-decode.txt
../EDID from OCDMacGeek/EDID_APP_610_ae22_6_edid-decode.txt
../EDID from vincek8s/EDID_APP_610_ae22_1_edid-decode.txt

	# target-default-ppmm: 8.58
	# front end: 5K only (even though mtdd overlay still lists both 5K and 6K modes)
	# 12 bit in overlay

#======================================================================
		find .. -path '*610*' -name '*ae2e*'
../EDID from AlexFila/EDID_APP_610_ae2e_1_edid-decode.txt
../EDID from AlexFila/EDID_APP_610_ae2e_3_edid-decode.txt
../EDID from cmsj/EDID_APP_610_ae2e_1_edid-decode.txt
../EDID from cmsj/EDID_APP_610_ae2e_3_edid-decode.txt
../EDID from elliottcable/EDID_APP_610_ae2e_3_edid-decode.txt
../EDID from elliottcable/EDID_APP_610_ae2e_5_edid-decode.txt
../EDID from elliottcable/EDID_APP_610_ae2e_8_edid-decode.txt
../EDID from elliottcable/EDID_APP_610_ae2e_9_edid-decode.txt
../EDID from Human Person/EDID_APP_610_ae2e_5_edid-decode.txt
../EDID from Human Person/EDID_APP_610_ae2e_7_edid-decode.txt
../EDID from nick82/EDID_APP_610_ae2e_3_edid-decode.txt
../EDID from nick82/EDID_APP_610_ae2e_5_edid-decode.txt
../EDID from OliZ/EDID_APP_610_ae2e_5_edid-decode.txt
../EDID from OliZ/EDID_APP_610_ae2e_7_edid-decode.txt
../EDID from straightMacin/EDID_APP_610_ae2e_1_edid-decode.txt
../EDID from straightMacin/EDID_APP_610_ae2e_3_edid-decode.txt
../EDID from straightMacin/EDID_APP_610_ae2e_4_edid-decode.txt
../EDID from straightMacin/EDID_APP_610_ae2e_5_edid-decode.txt
../EDID from straightMacin/EDID_APP_610_ae2e_7_edid-decode.txt
../EDID from straightMacin/EDID_APP_610_ae2e_8_edid-decode.txt

	# target-default-ppmm: 8.58
	# 5K + 6K
	# 10 bit in overlay

#======================================================================
		find .. -path '*610*' -name '*ae21*'
		find .. -path '*610*' -name '*ae23*'
		find .. -path '*610*' -name '*ae2d*'
../EDID from cmsj/EDID_APP_610_ae23_9_edid-decode.txt
../EDID from elliottcable/EDID_APP_610_ae23_1_edid-decode.txt
../EDID from Fhed3040/EDID_APP_610_ae23_2_edid-decode.txt
../EDID from gimarbazat/EDID_APP_610_ae23_2_edid-decode.txt
../EDID from henrymyf/EDID_APP_610_ae23_2_edid-decode.txt
../EDID from Human Person/EDID_APP_610_ae23_2_edid-decode.txt
../EDID from likegadgets/EDID_APP_610_ae23_3_edid-decode.txt
../EDID from OCDMacGeek/EDID_APP_610_ae23_5_edid-decode.txt
../EDID from OCDMacGeek/EDID_APP_610_ae23_7_edid-decode.txt
../EDID from vincek8s/EDID_APP_610_ae23_2_edid-decode.txt
../EDID from bigtiger/EDID_APP_610_ae2d_1_edid-decode.txt
../EDID from bigtiger/EDID_APP_610_ae2d_2_edid-decode.txt
../EDID from Dae/EDID_APP_610_ae2d_2_edid-decode.txt
../EDID from diego9/EDID_APP_610_ae2d_1_edid-decode.txt
../EDID from gimarbazat/EDID_APP_610_ae2d_3_edid-decode.txt
../EDID from straightMacin/EDID_APP_610_ae2d_6_edid-decode.txt
../EDID from wago/EDID_APP_610_ae2d_2_edid-decode.txt

	# target-default-ppmm: 7.32
	# no mtdd

#======================================================================
		find .. -path '*610*' -name '*ae2f*'
../EDID from AlexFila/EDID_APP_610_ae2f_2_edid-decode.txt
../EDID from cmsj/EDID_APP_610_ae2f_2_edid-decode.txt
../EDID from elliottcable/EDID_APP_610_ae2f_2_edid-decode.txt
../EDID from elliottcable/EDID_APP_610_ae2f_4_edid-decode.txt
../EDID from Human Person/EDID_APP_610_ae2f_6_edid-decode.txt
../EDID from nick82/EDID_APP_610_ae2f_4_edid-decode.txt
../EDID from OCDMacGeek/EDID_APP_610_ae2f_8_edid-decode.txt
../EDID from OliZ/EDID_APP_610_ae2f_6_edid-decode.txt
../EDID from straightMacin/EDID_APP_610_ae2f_2_edid-decode.txt
../EDID from AlexFila/EDID_APP_610_ae2f_2_edid-decode.txt
../EDID from cmsj/EDID_APP_610_ae2f_2_edid-decode.txt
../EDID from elliottcable/EDID_APP_610_ae2f_2_edid-decode.txt
../EDID from elliottcable/EDID_APP_610_ae2f_4_edid-decode.txt
../EDID from Human Person/EDID_APP_610_ae2f_6_edid-decode.txt
../EDID from nick82/EDID_APP_610_ae2f_4_edid-decode.txt
../EDID from OCDMacGeek/EDID_APP_610_ae2f_8_edid-decode.txt
../EDID from OliZ/EDID_APP_610_ae2f_6_edid-decode.txt
../EDID from straightMacin/EDID_APP_610_ae2f_2_edid-decode.txt

	# target-default-ppmm: 8.58
	# no mtdd

 

[theorist9]

I'm not sure why Apple would disable DSC if the Mac were capable. Without DSC, the USB ports cannot run at a full 4 Gbps (data).

My guess would be that they would disable it to ensure the complete absence of compression artifacts from the types of critical applications in which the XDR might be used. Yes, DSC is claimed to be visually lossless, but the one study I've found that supports this wasn't done independently, because it comes from VESA itself:
VESA study of DSC

I haven't been able to find multiple independent studies of DSC. I've only been able to unearth this one, which finds DSC is visually lossless in 2D applications, but not in some stereoscopic applications:

Study of DSC in Steroscopic Applications​

Also, are you referring to USB ports on the monitor, or USB ports on the Mac that share that TB driver? I wouldn't think the former were that important, compared to picture quality; and I'm not sure if the Mac's USB ports share a TB driver with the TB ports—the drivers for the TB ports may be dedicated.

I've received AGDCDiagnose (works on Intel Macs) for a few setups of the XDR. I would have to recheck them all to see what OS and GPU they were running on.

Sorry, I don't know how to interpret your code—is any of it giving the DSC status when a TB port is driving a single XDR only (on a DSC-capable Mac)?

DSC doesn't need to be used for a display that is only 4K60. DSC only needs to be used for a display if it exceeds HBR2 x4 bandwidth.

OK, you're saying that if you had an XDR plus a lower-res display, like a 4k, connected to a TB port, DSC would be used for the XDR only.

 

[joevt]

Also, are you referring to USB ports on the monitor, or USB ports on the Mac that share that TB driver? I wouldn't think the former were that important, compared to picture quality; and I'm not sure if the Mac's USB ports share a TB driver with the TB ports—the drivers for the TB ports may be dedicated.

USB ports of the display. The display has a USB controller in its Titan Ridge Thunderbolt controller. A hub is connected to that to provide multiple 5 Gbps ports for the display. The USB controller is capable of 10 Gbps but Apple chose a 5 Gbps hub (the Studio Display has a 10 Gbps hub). The host needs to send PCIe data to the USB controller but 38.9 Gbps of the 40 Gbps available to Thunderbolt is used for the display.

Sorry, I don't know how to interpret your code—is any of it giving the DSC status when a TB port is driving a single XDR only (on a DSC-capable Mac)?

Those are a list of XDR EDIDs that I've seen from people in this forum and elsewhere. The actual info about DSC can be found in the AGDCDiagnose output where those EDIDs originated. You can google for messages from those people to find the AGDCDiagnose output that they posted. AllRez includes AGDCDiagnose output but more importantly, it includes the list of modes and other info. The info about the current mode shows if it's using DSC or not.

IIUC, without DSC, the bandwidth required by the XDR is very close to the maximum 38.9346 Gbps available if you force dual HBR3.

38.9346 Gbps is the bandwidth used by the display. 40 Gbps is the available bandwidth of Thunderbolt (disregarding Thunderbolt overhead).

https://forums.macrumors.com/threads/thunderbolt-4-ports-on-the-m2-mini.2377383/post-31959586

Thus I concluded if you want to drive an XDR plus any other monitor from a single Mac TB port, you'd need DSC. [Note that I wasn't saying you'd need DSC for a 4k60 monitor; I was saying that, if you connected an XDR plus any other monitor to a single TB port, the bandwidth requirements would necessitate DSC.]

Right - if you want to get 6K60 10bpc from the XDR.

And it may be that you'd need DSC even if there were more bandwidth available, since it might be the case that, as soon as you try to drive more than just an XDR alone from a single port, dual-tile mode goes away, which means you'd need DSC in any case.

Right, Thunderbolt only gets two DisplayPort signals from the host and the XDR in dual tile mode would use them both up, just like a Studio Display in dual tile mode or an LG UltraFine 5K.

 

[spatlese44]

There’s some great info in the links below:

Thunderbolt 4 hub performance with 3 SSDs

What happens to read and write speeds of three SSDs connected to the same hub, and working at the same time? Can they exceed the maximum of 3 GB/s?

eclecticlight.co

M-series Macs

A collation of articles about M1, M2, M3 and M4 Macs. Setting up and getting started Choosing an Apple silicon Mac Making the leap from Mojave to Apple silicon Should you migrate to your new Mac, a…

eclecticlight.co