Hi Niklas,
On Mon, Dec 12, 2016 at 3:18 PM, Niklas Söderlund
<niklas.soderlund@xxxxxxxxxxxx> wrote:
> +/*
> + * Linear approximation for temperature
> + *
> + * [reg] = [temp] * a + b => [temp] = ([reg] - b) / a
> + *
> + * The constants a and b are calculated using two triplets of int values PTAT
> + * and THCODE. PTAT and THCODE can either be read from hardware or use hard
> + * coded values from driver. The formula to calculate a and b are taken from
> + * BSP and sparsely documented and understood.
> + *
> + * Examining the linear formula and the formula used to calculate constants a
> + * and b while knowing that the span for PTAT and THCODE values are between
> + * 0x000 and 0xfff the largest integer possible is 0xfff * 0xfff == 0xffe001.
> + * Integer also needs to be signed so that leaves 7 bits for decimal
> + * fixed point scaling, which amounts to a decimal scaling factor of 100.
> + */
> +
> +#define SCALE_FACTOR 100
What about using 128 instead?
Fixed point is much easier with shifts
(the compiler will turn multiplications in shifts where appropriate).
> +#define SCALE_INT(_x) ((_x) * SCALE_FACTOR)
> +#define SCALE_MUL(_a, _b) (((_a)*(_b)) / SCALE_FACTOR)
> +#define SCALE_DIV(_a, _b) (((_a)*SCALE_FACTOR)/(_b))
DIV_ROUND_CLOSEST()
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
