Pro Display XDR, M1 Macs, Display Stream Compression & the 3 Ports

[IllinoisCorn]

I am operating under the assumption the display stream compression issue that kept USB speeds to USB 2 (rear ports) unless you were using a new enough GPU is no longer an issue with the M1 Macs.

Can anyone tell me if M1 Macs hooked to an XDR have gimped USB 2 speed or are the ports full USB 3?

 

[joevt]

I know Apple removed support for DSC in Big Sur at least for Intel Macs - not sure if that applies to XDR.

For M1 Macs, you can use the script at https://gist.github.com/joevt/e862b0088ef58b9144877d01401bcee8 to check if the XDR display is using the tiled (dual HBR3) 6K mode (reduced USB performance) or the non-tiled (HBR2 with DSC) 6K mode (normal USB 3.0 performance).

I have yet to see anyone show that the tiled mode changes the USB controller to USB 2.0 only. It could be USB 3.0 with reduced bandwidth.

A USB 3.0 connection should report "Up to 5 Gb/s" in the USB tab in System Information.app. A USB 2.0 connection should report "Up to 480 Mb/s".

Full USB 3.0 bandwidth should allow ≈450 MB/s. A USB 3.0 connection with reduced bandwidth will give less than that.

This command will get the USB info that is shown in System Information.app:
system_profiler SPUSBDataType > systemprofiler.txt

This command will show how all the devices are connected:
ioreg -iw0 > ioreg_iw0.txt