Re: USB mouse protocol,

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Vojtech Pavlik wrote:

> On Wed, Apr 30, 2008 at 11:28:59AM +0200, xerces8 wrote:
> > Hi!
> > 
> > I'm curious about some details in the protocol used by USB mice.
> > A cursory look at the "Device Class Definition for HID 1.11" documents
> > tells me (note this is the first USB technical document I ever read)
> > that a mouse can tell the host the format (the protocol) used to report
> > data (movement, button state etc.).
> > 
> > Also a quick look into linuxv2.6.25/drivers/hid/usbhid/usbmouse.c suggests
> > that 8 bits are used for position.
> > 
> > So my questions are:
> >  - is the position data always 8 bits wide ?
> 
> No. The driver you need to look at is usbhid.ko, not usbmouse - that
> only works for the static "HID Boot Protocol", and is only useful in
> embedded devices.

Pretty hard to read there... Can I activate some debug output, to see what
my mouse is sending ?

> >  - when are reports sent ? Are they polled by host ? Or sent by the device
> > on its own ?
> 
> That depends on how you look at it. The host controller polls the device
> at a specified rate - typically 100Hz, but the device decides whether it
> will or won't send a report when polled.

100Hz is the linux default ? Is there an USB standard value ?

Regards,
David


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