Re: [PATCH 2/2] input: ad714x - use stage qty to split max_coord for wheel algo

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Sorry, it's flawed, this causes a skipped range near max_coord.
(i.e. from (max_coord - (max_coord/stage_num)/2) to max_coord)

Will need to investigate more.

On 2012-04-26, at 13:17, Jean-François Dagenais wrote:

> Using "end_stage - start_stage" yields "number of used stages -1".
> This makes the divisor smaller, hence the dividend greater.
> 
> So for example, with 8 (0..7) stages, and max_coord of 1024, the
> algo should figure out that 1024 should be split in 8, so 8 slices
> of 128. Instead, dividing by 7 will give bigger slices of 146.
> 
> While adding these "slices", when stages 7 and 0 are weighted to
> determine the abs_pos, a dead-zone appears where we are stuck at
> max_coord because of the bigger "slices" and the if that follows:
> "if abs_pos > max_coord, then abs_pos = max_coord"
> 
> Hence this commit, which re-uses variable "stag_num" initialized with
> the number of used stages.
> 
> Signed-off-by: Jean-François Dagenais <jeff.dagenais@xxxxxxxxx>
> ---
> drivers/input/misc/ad714x.c |    3 +--
> 1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/input/misc/ad714x.c b/drivers/input/misc/ad714x.c
> index 2cf26e5..29f5d10 100644
> --- a/drivers/input/misc/ad714x.c
> +++ b/drivers/input/misc/ad714x.c
> @@ -477,8 +477,7 @@ static void ad714x_wheel_cal_abs_pos(struct ad714x_chip *ad714x, int idx)
> 		ad714x->sensor_val[first_before] +
> 		ad714x->sensor_val[first_after];
> 
> -	sw->abs_pos = ((hw->max_coord / (hw->end_stage - hw->start_stage)) *
> -			a_param) / b_param;
> +	sw->abs_pos = ((hw->max_coord / stage_num) * a_param) / b_param;
> 
> 	if (sw->abs_pos > hw->max_coord)
> 		sw->abs_pos = hw->max_coord;
> -- 
> 1.7.9
> 

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