#include <stdio.h>
#include <stdint.h>

#include <math.h>

#include <fxp.h>

static fxp_t adc_val_to_pin_voltage(uint16_t adc_val)
{
	return fxp_div(
			fxp_mult(FXP_FROM_INT((int32_t)adc_val), fxp_div(FXP_FROM_INT(33), FXP_FROM_INT(10))),
			FXP_FROM_INT(4096));
}


static fxp_t calc_temperature_ntc(uint16_t adc_val)
{
	// note: all resistor values in kΩ! The factor 1000 is removed from the numbers!
	static const fxp_t ln_r_ntc_nom = 252323; // ln(47 kΩ) converted to fxp_t with 16 fractional bits
	static const fxp_t r1 = FXP_FROM_INT(10);
	static const fxp_t b_constant = FXP_FROM_INT(4125);
	static const fxp_t ntc_temp_nom_inv = 220; // 1/(273.15+25) * 2**16
	static const fxp_t celsius2kelvin = 17901158; // (273.15) * 2**16

	fxp_t v_r1 = adc_val_to_pin_voltage(adc_val);
	fxp_t v_ref = fxp_div(FXP_FROM_INT(33), FXP_FROM_INT(10));

	fxp_t r_ntc = fxp_div(fxp_mult(fxp_sub(v_ref, v_r1), r1), v_r1);

	fxp_t ln_r_ntc = fxp_from_float(logf(fxp_to_float(r_ntc)));

	fxp_t temp_k = fxp_div(FXP_FROM_INT(1),
			fxp_add(
				fxp_div(
					fxp_sub(
						ln_r_ntc,
						ln_r_ntc_nom),
					b_constant),
				ntc_temp_nom_inv));

	return fxp_sub(temp_k, celsius2kelvin);
}


int main(void)
{
	for(uint16_t adc_val = 128; adc_val < 4096; adc_val += 512) {
		fxp_t temperature = calc_temperature_ntc(adc_val);

		float tempf = fxp_to_float(temperature);
		float voltf = adc_val * 3.3f / 4096.0f;

		printf("%5.3f V => %7.2f °C\n", voltf, tempf);
	}
}