Re: [Qemu-devel] Absolute USB-HID device musings (was Re: VNC Terminal Server)

[Anthony Liguori <aliguori@us.ibm.com>]

I was looking through the Xorg evdev driver and it doesn't appear to 
support absolute coordinate reporting.  evdev is how the USB mouse would 
show up to userspace.  A little googling confirmed it for me:

http://lists.freedesktop.org/archives/xorg/2005-September/010140.html

USB wacom still seems the most promising to me but I fear getting it to 
work under Windows will be a pain.

Regards,

Anthony Liguori


Leonardo E. Reiter wrote:
> This is by no means a complete patch (do not apply it as it will break 
> usb-hid.c), but it adjusts the report descriptor in usb-hid.c to 
> provide position in 16-bits, and in absolute coordinates:
>
> Index: usb-hid.c
> ===================================================================
> RCS file: /cvsroot/qemu/qemu/hw/usb-hid.c,v
> retrieving revision 1.1
> diff -a -u -r1.1 usb-hid.c
> --- usb-hid.c   5 Nov 2005 16:57:08 -0000       1.1
> +++ usb-hid.c   8 Apr 2006 20:56:02 -0000
> @@ -117,7 +117,7 @@
>      0x15, 0x00, 0x25, 0x01, 0x95, 0x03, 0x75, 0x01,
>      0x81, 0x02, 0x95, 0x01, 0x75, 0x05, 0x81, 0x01,
>      0x05, 0x01, 0x09, 0x30, 0x09, 0x31, 0x15, 0x81,
> -    0x25, 0x7F, 0x75, 0x08, 0x95, 0x02, 0x81, 0x06,
> +    0x25, 0x7F, 0x75, 0x16, 0x95, 0x02, 0x81, 0x02,
>      0xC0, 0xC0,
>  };
>
> According to: 
> http://72.14.203.104/search?q=cache:wVYUTwc33f8J:www.usb.org/developers/devclass_docs/HID1_11.pdf+usb+hid+specification+absolute+relative&hl=en&gl=us&ct=clnk&cd=1 
>
>
> I'm still trying to figure out how the logical min/max apply if we are 
> to report absolute (unsigned) positions in 16-bits.  Obviously 8-bits 
> is not enough for absolute coordinates.  You could theoretically use 
> only 12-bits per coordinate but that would make life difficult I 
> think, and probably unnecessarily frugal in a software emulation.
>
> It's not clear to me [yet] how the scroll wheel comes into play, and 
> whether or not it (the dz coordinate) can be kept relative for ease of 
> implementation.  Also the code would need to be changed to report 
> coordinates in 16-bits rather than 8, and of course made to report 
> absolute coordinates (like from sdl.c, etc.)  Still it looks fairly 
> easy to implement - the USB spec is pretty simple.
>
> So to reiterate, my patch does virtually nothing - in fact it will 
> break usb-hid.c so please don't use it.  I was just illustrating how 
> to get it to report the device as providing 16-bit absolute 
> coordinates instead of 8-bit relative ones.  If anyone wants to chime 
> in with more info, I'd be glad to make this a discussion.  *If* using 
> the USB HID device only, not any real USB devices, can be done without 
> slowing down QEMU, then I think this is a great way to get a tablet 
> emulated without having to deal with drivers on either side.  Plus, in 
> the long run, it probably means other neat stuff like being able to 
> get away from ISA bus emulation, and also it's portable to other 
> targets (for example, OS-X on PPC would talk to the USB HID device the 
> same way theoretically), so it's likely the most portable and cleanest 
> option.
>
> Regards,
>
> Leo Reiter
>
> Brad Campbell wrote:
>> Apparently USB HID supports absolute input devices natively. Given we 
>> have a HID mouse driver of sorts in qemu I wonder if that is another 
>> avenue perhaps ?
>>
>>
>