Re: [libdc1394-devel] Receiving 2 packets per iso cycle from a single device

[David M. <dcm@MIT.EDU>]

On Thu, 2007-09-20 at 10:36 +0900, Damien Douxchamps wrote:
> Hi Stephan,
> 
> On Wed, 2007-09-19 at 01:54 +0200, Stefan Richter wrote:
> > Damien Douxchamps wrote:
> > > I am testing an IIDC camera (Grasshopper from Point Grey) that can send
> > > 2 packets per cycle in isochronous mode.
> > 
> > To the same channel or to different ones?
> 
> Yes, it's on the same channel. According to Point Grey this is within
> IEEE1394 specs, but I don't have a clue...
> 

The OHCI 1394 specification doesn't seem to like the idea of it.  This
is the first sentence of section 10.4.2 from the specs
(http://download.intel.com/technology/1394/download/ohci_11.pdf).

"Each isochronous receive DMA context can receive one packet per cycle
from one isochronous data channel."

Given that restriction, the only way I think it _might_ work is if you
enable multichannel support for a given DMA context, or if some OHCI
hardware doesn't obey the above restriction.  I believe that video1394
doesn't have any support for the multichannel capability, but maybe Juju
does?

-David