Re: [Qemu-devel] Absolute Mouse in VNC and debug ports patch

[Gerhard Wiesinger]

On Sat, 3 Apr 2010, Paul Brook wrote:

> > This is my first contribution to QEMU: I've written a virtual piece of
> > hardware (e.g. ports) that the mouse pointer can be used as an absolute
> > pointing device even with non USB devices, e.g. with DOS and doesn't need
> > any high memory usage USB driver. This is necessary for e.g. VNC remote
> > access, this was my primary motivation.
>
> Why not just use the existing vmmouse?

First I didn't know that QEMU has already implemented vmmouse. I'm very 
new to QEMU. After looking at the code vmmouse requires 386 instructions 
in the DOS driver to access the 32 bit port access (eax, ebx, etc.) which 
might be problematic in real mode. and even on 286 (don't know whether 
this is relevant or not). Further protocol is a little bit more complex to 
implement in Assembler in the DOS TSR and therefore performance would be 
lower (DOS polls the mouse, no standard event or interrupt based system 
specified).

> > To use it you need a mouse driver (e.g. cutemouse,
> > http://cutemouse.sourceforge.net/) and an QEMU mouse TSR.
> > Further the mouse TSR emulates also a HP-HIL 45911 tablet digitizer. This
> > device has been chosen because an Interrupt interface exists at INT 6Fh and
> > therefore it is relativly easy to emulate (all other devices I've evaluated
> >  use the serial port and are therefore much more complex to emulate)
>
> However emulating an actual tablet connected to the serial port means you
> don't need any custom guest software.

But I thing it is only relevant for very old software like DOS. Every 
modern OS has USB on board and therefore the USB tablet emulation is IHMO 
sufficient and works well. The guest software could also be implemented as 
option rom (~2k), then no TSR would be necessary. As the typical use case 
is for DOS I don't see any relevant problems here because resident TSR 
size is very small (~2k) and common practice in DOS. BTW: is it possible 
to load more than one option ROM at a time, e.g. SCSI and another?

> > Further I've written a simple logging debug ports functionality to debug the
> > driver
>
> This looks a lot like the existing isa-debugcon.

Is this in the development tree only? I had only a look at the stable 
release and didn't find anything.

Ciao,
Gerhard

--
http://www.wiesinger.com/