Re: [FFADO-user] FW to USB [was: Firewire Audio Setting RME FF400 into Ubuntu 20.10]

[Jonathan W. <jw...@ju...>]

On Wed, Nov 25, 2020 at 11:26:41AM +0100, Michele Perrone wrote:
> USB and FireWire are two completely different protocols, you can't get
> one from the other. In theory, it could be done: in practice, it's too
> complicated.

Well expressed.  Trying to make a USB to firewire adapter would be extremely
difficult because there is almost no overlap between the USB and firewire
approaches to data transfer.  Historically there's also been a gap between
the sustained transfer rates possible from firewire compared to USB,
although USB 3 has mostly addressed that.  Probably the only way to make
such a hypothetical adapter would be to do a pass-through arrangement, but
this would require implementation of a full firewire host controller on the
far side of the USB link.  I also have a suspicion that the transfer
characteristics of USB probably wouldn't provide the timing required for
reliable operation of firewire devices (especially audio interfaces).  Even
if this could be dealt with, operating systems would require drivers for
such a device (I don't know if there's a class compliant specification for
something like this, or if the support requires vendor-specific drivers). 
As you said, this would quicky get very complicated and is unlikely to be
worth the effort.

> Also don't be fooled by USB-C connectors: they are used to carry
> Thunderbolt-3, but in the majority of cases they carry just plain USB
> protocol. Always check the specifications.

This is a good point.  If an adapter is a USB-thunderbolt unit then many of
the issues noted above would come into play.  I am not sure how
USB-thunderbolt adapters are designed to work with operating systems (on the
other hand, thunderbolt-3 to thunderbolt-2 adapters are much easier since I
understand that both sides are essentially speaking PCIe).  At some level
the PCIe bus associated with the thunderbolt port must be made visible to
the operating system, suggesting some kind of pass-through arrangement be
used.  However, it may be that the use of USB places limits on the kinds of
thunderbolt devices these adapters can support.

I suspect that in order to work reliably with audio interfaces, any
thunderbolt 2 adapter would need to utilise the thunderbolt-3 protocol on
the computer side rather than USB.  However, since I don't currently possess
any computers with thunderbolt ports of any kind I have no first-hand
experience with this.  Having said that, the original post in the parent of
this sub-thread indicates that there are USB-thunderbolt adapters, so I
would be interested to know how these are designed to work and what view of
the thunderbolt port they provide to the operating system.

To directly answer the original question in this sub-thread:

> On 11/25/20 11:04 AM, m.eik michalke wrote:
> > is it possible to use firewire audio devices through an adapter to USB
> > in general?  is this a thing or more like "don't even try"?  asking for
> > a laptop ;)

I have not heard of any standalone USB-firewire adapter.  I therefore don't
believe this is possible in general.

Regards
  jonathan