Rune Allnor wrote:
> On 22 Mar, 08:38, minfitl...@yahoo.co.uk wrote:
>> What is considered real-time? How much latency would be necessary for
>> it to be no longer real-time? The application is adaptive filtering.
>> Somebody told me that real-time is strictly one sample in and one
>> sample out but most of the processors I have met don't work that way
>> any more - they work on buffers of data and surely all real-time
>> filters have some latency or is one sample all that is required?
>
> "Real time" means that the data are processed as they come in,
> and that this processing is done inside an acceptable latency.
> In a phone system, this "acceptable latency" may be on the
> order of milliseconds.
>
> Where I work, the "acceptable latency" is 24 hours. It is still
> a real-time system.

The last time I built DSP for the telephone network, the acceptable
latency was 3 sample times - 375us. One to deserialise, one to
serialise, and just one left for the processing delay in the middle. :-)

A true real time application typically doesn't have an "acceptable"
latency. It has a hard and well defined latency, it absolutely
positively must meet under all circumstances. For a control loop that
hard latency is typically very small for acceptable performance. For a
satellite TV decompressor it might be quite long. Nonetheless, the
incoming data will *always* be accepted without ever losing a bit, and
the output will be provided a very much fixed delay after the input data
is received.

Steve