Add conversion function for resistance to temperature conversion and add it to thept command of the shell

stm-firmware/Makefile

@@ -43,6 +43,8 @@ CFILES += stm-periph/unique-id.c
 
 CFILES += calibration.c
 
+CFILES += temp-converter.c
+
 DEFINES += -DDEBUGBUILD
 #TODO
 

stm-firmware/include/reflow-controller/temp-converter.h

@@ -0,0 +1,31 @@
+/* Reflow Oven Controller
+ *
+ * Copyright (C) 2020  Mario Hüttel <mario.huettel@gmx.net>
+ *
+ * This file is part of the reflow Oven Controller Project.
+ *
+ * The reflow oven controller is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * GDSII-Converter is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GDSII-Converter. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __TEMP_CONVERTER_H__
+#define __TEMP_CONVERTER_H__
+
+/**
+ * @brief Convert PT1000 resistance to temperature in degrees celsius
+ * @param resistance PT1000 resistance value
+ * @param[out] temp_out Temperature output
+ * @return 0 if ok, -1 if value is below conversion range, 1 if value is above conversion range,-1000 in case of pointer error
+ */
+int temp_converter_convert_resistance_to_temp(float resistance, float *temp_out);
+
+#endif /* __TEMP_CONVERTER_H__ */

stm-firmware/shell.c

@@ -8,6 +8,7 @@
 #include <reflow-controller/systick.h>
 #include <stm-periph/unique-id.h>
 #include <reflow-controller/calibration.h>
+#include <reflow-controller/temp-converter.h>
 
 #ifndef GIT_VER
 #define GIT_VER "VERSION NOT SET"
@@ -106,6 +107,9 @@ static shellmatta_retCode_t shell_cmd_pt1000_res(const shellmatta_handle_t   han
 	int pt1000_status;
 	enum adc_pt1000_error pt1000_flags;
 	char display_status[100];
+	float temp;
+	int temp_conv_status;
+	const char *temp_prefix;
 
 	display_status[0] = 0;
 
@@ -125,7 +129,22 @@ static shellmatta_retCode_t shell_cmd_pt1000_res(const shellmatta_handle_t   han
 		strcpy(display_status, "VALID");
 	}
 
-	shellmatta_printf(handle, "PT1000 resistance: %.2f Ohm [%s]\r\n", resistance, display_status);
+	temp_conv_status = temp_converter_convert_resistance_to_temp(resistance, &temp);
+	switch (temp_conv_status) {
+	case 1:
+		temp_prefix = ">";
+		break;
+	case -1:
+		temp_prefix = "<";
+		break;
+	case 0:
+		/* Expected fallthrough */
+	default:
+		temp_prefix = "";
+		break;
+	}
+
+	shellmatta_printf(handle, "PT1000 resistance: %.2f Ohm (%s%.1f °C) [%s]\r\n", resistance, temp_prefix,temp, display_status);
 
 	return SHELLMATTA_OK;
 }

stm-firmware/temp-converter.c

@@ -0,0 +1,74 @@
+/* Reflow Oven Controller
+ *
+ * Copyright (C) 2020  Mario Hüttel <mario.huettel@gmx.net>
+ *
+ * This file is part of the reflow Oven Controller Project.
+ *
+ * The reflow oven controller is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * GDSII-Converter is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GDSII-Converter. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <reflow-controller/temp-converter.h>
+#include <reflow-controller/temp-converter-data.h>
+#include <helper-macros/helper-macros.h>
+
+static const float temp_lookup[(TEMP_CONVERSION_MAX_RES-TEMP_CONVERSION_MIN_RES) / TEMP_CONVERSION_RES_STEP+1] = {TEMP_CONVERSION_ARRAY_DATA};
+
+int temp_converter_convert_resistance_to_temp(float resistance, float *temp_out)
+{
+	int ret_val;
+	unsigned int i;
+	unsigned int lower_idx = COUNT_OF(temp_lookup) - 1;
+	float diff_to_low_resistance;
+	float diff_high_low;
+	float low;
+
+	/* Check pointer */
+	if (!temp_out)
+		return -1000;
+
+	if (resistance < TEMP_CONVERSION_MIN_RES) {
+		*temp_out = temp_lookup[0];
+		ret_val = -1;
+		goto return_ret_val;
+	} else if (resistance > TEMP_CONVERSION_MAX_RES) {
+		*temp_out = temp_lookup[COUNT_OF(temp_lookup)-1];
+		ret_val = 1;
+		goto return_ret_val;
+	}
+
+	/* Resistance is in range */
+	ret_val = 0;
+
+	/* Calculate lower index for given reistance */
+	for (i = 1; i < COUNT_OF(temp_lookup); i++) {
+		if (resistance <= TEMP_CONVERSION_MIN_RES + TEMP_CONVERSION_RES_STEP * i) {
+			lower_idx = i - 1;
+			break;
+		}
+	}
+
+	/* Get the lower temperature limit of the current range */
+	low = temp_lookup[lower_idx];
+
+	/* Difference to higher limit */
+	diff_high_low = temp_lookup[lower_idx+1] - low;
+
+	/* Resistance difference to lower limit's resistance value */
+	diff_to_low_resistance = resistance - (float)(TEMP_CONVERSION_MIN_RES + TEMP_CONVERSION_RES_STEP * lower_idx);
+
+	/* Calculate output temperature */
+	*temp_out = (diff_to_low_resistance / TEMP_CONVERSION_RES_STEP) * diff_high_low + low;
+
+return_ret_val:
+	return ret_val;
+}