ntc.c

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#include "hw/hw_ntc.h"
#include "hw/ntc_map.h"

#include <cfg/debug.h>

#include <drv/ntc.h>

DB(bool ntc_initialized;)

static size_t upper_bound(const res_t *orig_table, size_t size, res_t val)
{
    const res_t *table = orig_table;

    while (size)
    {
        size_t pos = size / 2;
        if (val > table[pos])
            size = pos;
        else
        {
            table += pos+1;
            size -= pos+1;
        }
    }

    return table - orig_table;
}


deg_t ntc_read(NtcDev dev)
{
    const NtcHwInfo* hw = ntc_hw_getInfo(dev);
    const res_t* r = hw->resistances;

    float rx;
    size_t i;
    deg_t degrees;

    rx = ntc_hw_read(dev);


    i = upper_bound(r, hw->num_resistances, rx);
    ASSERT(i <= hw->num_resistances);

    if (i >= hw->num_resistances)
        return NTC_SHORT_CIRCUIT;
    else if (i == 0)
        return NTC_OPEN_CIRCUIT;

    /*
     * Interpolated value in 0.1 degrees multiplied by 10:
     *   delta t          step t
     * ----------  = ----------------
     * (rx - r[i])   (r[i-1] - r [i])
     */
    float tmp;
    tmp = 10 * hw->degrees_step * (rx - r[i]) / (r[i - 1] - r[i]);

    /*
     * degrees = integer part corresponding to the superior index
     *           in the table multiplied by 10
     *           - decimal part interpolated (already multiplied by 10)
     */
    degrees = (i * hw->degrees_step + hw->degrees_min) * 10 - (int)(tmp);

    //kprintf("dev= %d, I=%d, degrees = %d\n", dev, i , degrees);

    return degrees;
}


void ntc_init(void)
{
    NTC_HW_INIT;
    DB(ntc_initialized = true;)
}