Plans for hal 0.5.x

David Zeuthen david at
Tue Dec 14 09:56:28 PST 2004

On Tue, 2004-12-14 at 19:03 +0300, Andrei Yurkevich wrote:
> > Well, since each connection method (USB, serial, bluetooth, etc) is
> > actually a hardware device itself, why not show the PDA as a _child_ of
> > that device?  We are working with parent/child relationships as a
> > fundamental property of HAL already.  Therefore you wouldn't necessarily
> > need a "pda.palm.serial_interface" property, you could just ask for the
> > "device.interface" (or something) property of the parent of the PDA
> > object.
> I am absolutely agreed with you about having a PDA device as a child 
> node of the serial interface, but still I think that creating that node 
> and filling it with pda-specific information should be done outside of 
> hal. 

Again, the program doing this should run in the desktop session anyway
and already knows, so it needs not to tell hal about it.

> For that reason, HAL could just query the serial interface about 
> what's on the other side and if that is PDA it could simply tag the 
> serial interface. Then some callout or daemon that knows how to deal 
> with different kinds of PDAs (or at leas that kind of PDA connected 
> there) could create the PDA node below the serial port and set the 
> necessary properties there.

You can't really probe a serial port since that may interfere with it's
operation. I don't think hal should attempt to do that, that's a can of
worms. E.g. if you really want to support legacy ports in your desktop
software, you need to take the painful route and do it from your desktop
sessions - e.g. the "Detect Modem" or "Detect PDA" button and then deal
with it. No such thing as a free lunch (reminds me; I should go to
lunch :-)).

> > It would seem like having that property on both the PDA _and_
> > the actual device itself would be redundant.  (however, I can see it
> > being useful on the PDA so I'm not really objecting to having it there).
> In some cases, the fact that the serial port is there does not 
> necessarily mean that PDA is available. For instance, when you plug in a 
> Pocket PC PDA via USB, you will get a USB device and a USB-serial 
> interface, but until you start the software that establishes a 
> connection with your PDA you are not able to do anything useful with it.

No, but the fact that desktop software knows that there is a 100% chance
of the serial port having a PDA in the other end allows it to start
doing things with it. Like initiating a sync.

That's why I only think it's useful to consider plug and play devices.


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