linux-kernel - Re: [RFC 1/2] Input: ff, add FF

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Date:	Thu, 19 Apr 2007 17:38:05 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Dmitry Torokhov <dtor@...ightbb.com>
Cc:	johann deneux <johann.deneux@...il.com>,
	linux-kernel@...r.kernel.org, stenyak@...il.com,
	linux-input@...ey.karlin.mff.cuni.cz
Subject: Re: [RFC 1/2] Input: ff, add FF_RAW effect

Dmitry Torokhov napsal(a):
> I have been thinking about this and I don't think that exporting motor
> data is a good idea, at least not in case of Phantom driver. The fact
> that there are 3 motors is a hardware implementation detail and it
> is not interesting for general application.

Ok, so what about torques (despite it's still something like FF_RAW or motor
descriptor)? It seems not to be so bad called effect name -- not only
phantom uses torques on motors as an unit of force, for example I get this
by quick googling:
http://www.caip.rutgers.edu/~bouzit/lrp/glove.html
They use there some motors with 14 torque values too, so the phantom isn't
the only device which uses this approach.

> My understanding that the end result of controlling these 3 motors

Actually there is also a version with 6 motors :).

> is a force vector (I don't know if there is such english term, this
> is a literal translation from russian) applied to user's hand.

Better say torques vector. You must compute a torque for each place from the
3d (or bigger) vector of forces in different way for each device that exists
-- this means forces are not independent unit, torques are in the meaning of
layer which doesn't care about what is connected above and below it.

> If we are interested in using FF API we need to come up with a way
> to express this effect without exposing implementation details of
> one particular device.

Still, torques are better named raw/motor values, which goes to the device
and I'm sceptic about inventing something class-better than this.

regards,
-- 
http://www.fi.muni.cz/~xslaby/            Jiri Slaby
faculty of informatics, masaryk university, brno, cz
e-mail: jirislaby gmail com, gpg pubkey fingerprint:
 B674 9967 0407 CE62 ACC8  22A0 32CC 55C3 39D4 7A7E


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