[RFC] PDA as a TCP graphic tablet?

[Guennadi Liakhovetski]

On Thu, 29 Dec 2005, Glynn Clements wrote:

> 
> Guennadi Liakhovetski wrote:
> 
> > > > If there is already a driver I could reasonable (ab)use, ideally it should 
> > > > only use read/write on the fd. If it uses ioctl's, well, that would mean I 
> > > > would have to write a kernel driver too. Not too dramatic, but not exactly 
> > > > the ideal solution.
> > > 
> > > Have the server-side client use a pty, which X should be able to use
> > > in the same way as a physical serial port.
> > 
> > Aha, thanks, wouldn't think of a pty myself. Wouldn't an xserver
> > accept a named pipe/socket?
> 
> Named pipes are unidirectional, so they won't work if the driver
> assumes a bidirectional data flow (even if it's only sending an
> initialisation sequence then receive-only thereafter).

I hoped 1 direction would be enough, I'll double-check that, thanks.

> Sockets can't be opened with open(); you have to use connect(). A
> driver written for a serial device will use open().
> 
> Neither of those will work if the driver uses tty ioctls (e.g. setting
> the baud rate or enabling "raw" mode) and aborts on failure.
> 
> If you were modifying an existing driver, the above issues could
> probably be eliminated with a minimal amount of effort. But that
> doesn't help if you want to use an unmodified driver.
> 
> The advantage of a pty is that it's behaviour is almost
> indistinguishable from a physical serial interface, so anything which
> works with serial interface will probably work just as well with a
> pty.

Ok, I'll see if the X' wacom driver ever writes and / or uses ioctls.

> > Anyway, the main question remains - which X-driver to attach the
> > "graphic tablet"?
> 
> If it was me, from amongst the drivers which can use a serial
> interface, I'd just use whichever one had the easiest protocol to
> implement (i.e. either the simplest or the best documented protocol). 
> I don't have much experience with graphics tablets, so I can't say
> which driver that would be.

Heh, the problem is - I don't have any experience with them:-) If I did 
have experience, I probably had one, so, I wouldn't need to fake one with 
a touchscreen:-) And another problem is - I haven't found too many, in 
fact, only 1 so far - wacom:-) I guess, I'll have to ask the guys how I 
can pretend being a small primitive wacom tablet:-)

Thanks
Guennadi
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Guennadi Liakhovetski