On 26 Apr, Terry Hancock wrote:
> On Monday 26 April 2004 02:28 pm, Stefan Richter wrote:
>> Video data transmission over the 1394 port works probably as
>> isochronous transmission (data rate guaranteed, data integrity
>> not guaranteed).
[...]
> I'm a little concerned about this "isochronous"
> concept -- sounds like I might lose data in the process.
As Dan already wrote, there is hardly anything to worry about.
The advantage of isochronous transactions is, the sender can rely
on his share of bus bandwith. Isochronous packets provide also
CRCs for packet header and for data, and there are also means for
synchronization between sender and listeners. Hence it is
possible to detect most data integrity problems and perhaps to
react on them. However the sender does not check itself if the
listeners received everything properly.
> I guess this means I need
> to be concerned about the throughput of the 1394 port. Do they
> vary, or is it just a case of "Firewire is firewire"?
The throughput of FireWire cards for PCs is nowadays always 400
Mbit/s or 800 Mbit/s minus protocol overhead. Overhead is also
independent of the card and, in case of isochronous transmis-
sions, exactly predictable for the sender. The pricier 800 Mbit/s
cards a.k.a. IEEE 1394-B cards are not relevant for video in the
consumer range yet.
In some cases people see performance problems on the PC's side,
e.g. when the harddisk controller does not utilize DMA or when
there is a PCI/BIOS related incompatibility with Linux.
-- Stefan Richter -=====-=-=-- -=-- ==-== http://arcgraph.de/sr/ ------------------------------------------------------- This SF.net email is sponsored by: The Robotic Monkeys at ThinkGeek For a limited time only, get FREE Ground shipping on all orders of $35 or more. Hurry up and shop folks, this offer expires April 30th! http://www.thinkgeek.com/freeshipping/?cpg=12297 _______________________________________________ mailing list Linux1394-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux1394-userReceived on Tue Apr 27 22:30:57 2004
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