Re: USB mouse protocol,

[Vojtech Pavlik <vojtech@suse.cz>]

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.

>  - 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.

-- 
Vojtech Pavlik
Director SuSE Labs