Late 2013 Thunderbolt bus

[michael_aos]

Late 2013 Mac Pro.

I have some "Up to" 20 Gb/s x1 and 10Gb/s x2 devices.

I know if you chain a Thunderbolt 2 device off a Thunderbolt 1 device, you'll only get Thunderbolt 1 speeds.

My question is whether having both a Thunderbolt 1 and Thunderbolt 2 device on the same bus (i.e. - Bus 1) (since there are 2x Thunderbolt ports on Late 2013 Mac Pro for Thunderbolt Bus 1) will slow everything on the bus down to Thunderbolt 1 speeds?

Or can, for example, port-1 of Bus 1, communicate at 20Gb/s x1 and port-2 of Bus 1 communicate at 10Gb/s x2?
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[deconstruct60]

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My question is whether having both a Thunderbolt 1 and Thunderbolt 2 device on the same bus (i.e. - Bus 1)

It is same TB controller more so than same "TB bus" (as Apple appears to use the term).

Or can, for example, port-1 of Bus 1, communicate at 20Gb/s x1 and port-2 of Bus 1 communicate at 10Gb/s x2?
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Pragmatically no in most cases with input/output in both directions, but for a different reason that the limitation when daisy chaining.

TB ports are not additive. The two ports provisioned by a single controller share the same inputs. If this is encoded PCI-e data traffic even if the "all TB v2.0" chain in port 1 could send data 20Gb/s speeds, the in/outbound data on the other port will eat into the same x4 PCI-e v2 interface the controller has with the host system. ( that shared PCI-e v2 interface and DP inputs being the "TB bus". In that sense yes... but it is really not a Thunderbolt data traffic issue. It is really a getting off the TB network issue. )


If the TB devices were passing data to one another and not all trying to send it to just one device (e.g., the host computer) then no there not a slow down except as transition to a v1 device.

Same with daisy chain. host <--> TB2-dev1 <--> TB2-dev2 <---> TB1-dev <---> TB2-dev3

in/out bound all the way out to TB2-dev2 is TB v2. TB1 device limits it and everything else downstream to TB v1 speeds.