Review: CalDigit's Element Hub Delivers Flexible Thunderbolt and USB Support

[joevt]

Thanks - that's really helpful. The Caldigit article doesn't make it clear what the data path is when connected to a TB4 host.

Thunderbolt 4 Host will use it's USB controller to connect to the USB hub of the Thunderbolt 4 Hub. The USB data (≈10 Gbps) between the USB controller and the USB hub is tunnelled through the Thunderbolt 4 connection (40 Gbps).

Thunderbolt 3 Host will use USB controller of Thunderbolt 4 Hub. PCIe data between the host Thunderbolt controller's PCIe bridge and the Thunderbolt hub's Thunderbolt controller's PCIe bridge is tunnelled (≈22 Gbps) through the Thunderbolt 3 connection (40 Gbps).

So, I think what you're saying is that - as far as downstream USB 2 & 3.1 gen 1 bandwidth and latency is concerned this is not going to be any better than my current setup of an old-school 7 port USB3 hub connected to a TB4 port on my Studio. (and, just like that hub, ports 4-7 are provided by a second internal USB hub).

Correct.

One of my issues is that I have a number of USB 2 devices - 2 audio interfaces and several USB MIDI devices - which may use a piddling amount of bandwidth by modern standards but do need low latency and are best connected as close to the 'root' of the USB tree as possible (I already understand that the USB 2 tree is separate from & parallel to the USB 3 tree so even on USB 3 hardware they're still subject to USB2 era bandwidth and latency issues). They'll probably be fine on a hub, but I'd certainly rather avoid them going through a cascade of hubs... I think in my case the role of something like the Element hub would be to consolidate other devices to free up ports on the Mac for Audio devices.

The tunnelling process (either tunnelled USB for Thunderbolt 4 hubs or tunnelled PCIe for Thunderbolt 3 hubs may add some latency compared to a non-Thunderbolt connected USB hub. I don't know what's best:

- CPU -> PCIe -> Thunderbolt 3 tunnelled PCIe -> Thunderbolt connected USB controller -> USB port
- CPU -> PCIe -> USB controller -> Thunderbolt 4 tunnelled USB -> Thunderbolt connected USB hub -> USB port
- CPU -> PCIe -> USB controller -> USB hub -> USB port

Apple Silicon Macs don't do "-> PCIe ->" since the controllers are integrated into the CPU. Well, it doesn't need to be real PCIe.

Alternatively, I suppose there's this:

External Thunderbolt 3 to USB Controller - 3 Dedicated USB Host Chips - 1 Each for 5Gbps USB-A Ports

Convert your laptop’s Thunderbolt 3 port into multiple USB controller ports, with one USB-C and one USB-A port supporting 10Gbps, plus a daisy-chainable TB3 por

www.startech.com

...or getting a PCIe enclosure and putting in some USB controller cards, but that's getting a bit ridiculously expensive.

The linked StarLink Thunderbolt 3 dock uses these chips:
- ASM1142 - PCIe 5GT/s x2 = 8 Gbps : reduces the max performance of USB 10 Gbps from 9.7 Gbps down to 8 Gbps.
- ASM1042A - PCIe 5GT/s x1 = 4 Gbps : slightly reduces the max performance of USB 5 Gbps (USB 5 Gbps is actually 4 Gbps but the 4 Gbps of PCIe has some overhead - this means 5 Gbps USB from the ASM1142 will be slightly better - closer to the 4 Gbps data max - than the 5 Gbps USB from the ASM1042A; the same is true of the FL1100 used in the CalDigit TS3 Plus)