RE: Re: Spec revisions...

[Kevin Hawkins]

> -----Original Message-----
> From: Patrick Lidstone [mailto:<a
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> Sent: 30 March 2003 12:17
> To: <a
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> Subject: [xAP_developer] Re: Spec revisions...
>
> --- In <a
href="/group/xAP_developer/post?postID=Lcp4kaE1pmNfU7q77LLdGjd-S3xtTDf37lLCAcg87H0yzgFYo1igvx_IHSJMJihDRshepIppzLEnJOOd0Ca0cH5QoKA">xAP_developer@xxxxxxx</a>,
Stuart Booth <lists@s...> wrote:
> > On Wed, 26 Mar 2003 09:38:24 -0000, "Patrick Lidstone"
> > <patrick@l...> wrote:
> >
> > >At the moment, senders and receivers use schema which
identify
> > >functionality which is specific to the device. The idea of
event
> > >addressing is the introduction of -abstract- events which are
not
> > >tied to a specific device(s), but indicate a generic, system
wide
> > >change of status.
> >
> > Do you happen to have an example of what you mean by this?
> >
> > Taking your audio.mute example, I'm thinking that an untargetted
> > message (one-to-many) achieves the same result.
>
> The problem is that any receiver of a "mute" message has to
> explicitly be able to identify each and every possible source for the
> event.
>
> Suppose I have a four MP3 players, a TV and a home cinema system all
> of which have different target addresses and all of which might be
> required to respond simultaneously to an "audio.mute".
>
> Suppose that an "audio.mute" event can be generated by: a
caller id
> box, an infra-red remote control (ie. manually), by a text to speech
> announcement system (so that the announcement can be heard), and by a
> doorbell interface.
>
> Each of those individual senders has to be configured to send 6
> target messages [OK, I agree that it *may* be possible to target the
> MP3 players with a single message, but the basic principle holds].
> And, worse, if a new device is added to the network, they have to be
> reconfigured. An addiitonal minor niggle is that these messages can't
> be sent truly simultaneously, so there will be fractional delays
> between each device being silenced.

I think we need to revisit the postponed 'groups/scenes' addition to xAP
that was dropped from the last spec - I still hold that a lot of these
issues are elegantly solved by this mechanism. Particularly when you
consider that mutes maybe localised to areas as well - eg top floor,
outside
etc. I am intrigued by the possibility of event based addressing but really
don't understand clearly yet it's intentions.

>
> The same argument replies round the other way if you use source
> addressing...
>
> > A many-to-many notification sounds almost like an anonymous
> broadcast.
> > ie no source.
>
> The source is still present, but is ignored. Conceptually I guess you
> could think of it as an anonymous broadcast.
>
> > >Some pieces of hardware
> > >may be able to support multiple logical functions that are
totally
> > >unrelated (e.g. Ian B's relay control, which is also capable
of
> input
> > >switch sensing, my rabbit board which can support two
completely
> > >different serial devices concurrently). The fact that these
two
> > >functions happen to be implemented on the same device is
complete
> co-
> > >incidence, and they really should be independently addressed.
We
> > >don't currently allow for that in the spec, and I think we
should.
> >
> > Isn't that what the subaddress was intended for?
>
> Yes and no. It was the original intention behind subaddressing, but
> it only really works for related functionality. Perhaps the relay
> board is a special case, but the switches and the relays have no
> direct logical or functional relationship - and it doesn't make any
> sense for them to share the same core address.

I think the original view was that the heartbeat reflected that all devices
that were covered by the software were running OK. If a device had one
processor and several serial ports and a couple of parallel ports then the
sub addresses took care of the ports as such and the heartbeat the xAPp .
This enabled physical boxes to be quickly identified. Having said that I
don't see a big problem if you wanted to create separate heartbeats for
some
ports either - after all that's sort of how the I/O on a PC currently works
with say the Meteor. It's really just a case of the granularity of the sub
addressing and not dividing up to an extent that several source addresses
have to be stored in one low capacity receiver.

Kevin