Re: Hard and soft real time with Ada

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Mon, 17 May 2010 03:29:02 -0700 (PDT), sjw wrote:

> On May 17, 9:30�am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
> 
>> Hmm, I doubt USB can be considered real-time. But I see no obvious reason
>> why a computer vision application could not tolerate some jitter (say
>> 100�s). I guess you just do not need "very hard" real-time.
> 
> But is there anything about USB which makes the latencies etc for a
> particular set of devices unbounded? If not, why shouldn't USB be used
> in an appropriate application?

The word "bus" probably. In a comparable case when industrial Ethernet is
made RT, they usually make some master controlling the frames on the wire
or else do them time triggered. One certainly could do something alike for
USB, if anybody cared. But no standard device would work with that.

On the other hand I think that the major contributor to the jitter is not
the hardware but the application software. One certainly could have
reasonably short stable latencies over USB.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de