Added test program for the NTC calculation

.gitignore

@@ -7,3 +7,7 @@
 
 # generated config HEX files
 utils/*.hex
+
+test/*
+!test/*.c
+!test/Makefile

test/Makefile

@@ -0,0 +1,18 @@
+BUILD=debug
+
+CFLAGS = -ggdb -I../fxplib/include -DPOINTPOS=16 
+LDFLAGS = -lm
+
+FXPLIB_A = ../fxplib/lib/debug/libfxp_x86.a
+
+default: ntc_calculation
+
+export CFLAGS
+export BUILD
+export PREFIX
+export POSTFIX = x86
+$(FXPLIB_A):
+	cd ../fxplib && $(MAKE)
+
+ntc_calculation: ntc_calculation.c $(FXPLIB_A)
+	gcc -o $@ $(CFLAGS) $(LDFLAGS) $^

test/ntc_calculation.c

@@ -0,0 +1,55 @@
+#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);
+	}
+}