On Tuesday 14 of June 2011 17:20:52 you wrote: > > Hello, > > > > this patch fixes two issues with autocentering in lgff driver. Current > > implementation incorrectly assumes that the saturation force is always > > 0x80 which is > > inconsistent with behavior of the official driver. It also makes it > > impossible to disable autocentering on some wheels - at least Logitech > > Formula Force RX is > > the case. Values of stiffness coefficient were also calculated > > incorrectly. Formula used in this patch appears to generate the same > > commands as the official > > Logitech drivers. The patch also fixes two minor coding style issues. > > Hi Michal, > Can you elaborate more on the difference between stiffness and saturation? > And how these might work in the Linux FF system which only accounts a > single parameter. > > On my reverse engineering of the Wii Wheel (1) I noticed that the > AutoCentre consisted of 3 variables, but did realise the precise details. > Perhaps I can factor in a similar adjustment.... > > BTW - I also discovered some other modes of feedback beyond AutoCentre and > CF which might be applicable to other Logitech wheels. (2) > > Simon > > 1. > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=dr > ivers/hid/hid-lg4ff.c;h=fa550c8e1d1bc639bd3e9c34a299903391bca44a;hb=3a2289a4 > a317e0290a8bc7af28c62c9830cb12e5#l72 > > 2. http://wiibrew.org/wiki/Logitech_USB_steering_wheel Sure, but please don't take it like I have some inside knowledge of Logitech FF implementation. I've been given few bits of useful information, the rest I figured out from sniffed USB communication. Centering force seems to be modeled as a spring effect. Force created by a spring can be calculated as "F = -k*x" where F = force, k = stiffness coefficient and x = deflection from centre. The higher the k is, the faster the centering force increases when the wheel is turned. Saturation force seems to be the limit centering force, so when kx > saturation_force => F = saturation_force. Logitech driver has a slider which sets the centering force from 0 % to 150 % (it's actually from 0 % to 200 %, at least the values in the command suggest so) and both the stiffness coeff and saturation force increase gradually with the centering force according to the formula I provide in the patch, so just the magnitude value is enough. It looks like the stiffness coeff actually wraps around, because 0 = no stiffness, 7 = max stiffness, 8 = low stiffness, 15 = max stiffness. It'd be interesting to see if you can observe the same behavior on the Wii wheel. As for the other FF effects, I guess these are things like "rumble" etc. I'm planning to look into it more when I'll have some extra free time. Regards, Michal. -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
