Add FIR filter code

stm-firmware/fir-filter.c

@@ -0,0 +1,64 @@
+/* Reflow Oven Controller
+*
+* Copyright (C) 2021  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.
+*
+* The Reflow Oven Control Firmware 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 the reflow oven controller project.
+* If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <reflow-controller/fir-filter.h>
+
+void fir_filter_init_null(struct fir_filter_fixed *filter)
+{
+	uint32_t idx;
+
+	if (!filter)
+		return;
+	filter->put_idx = 0U;
+	for (idx = 0; idx < filter->tap_count; idx++)
+		filter->data = 0;
+}
+
+
+int32_t fir_filter_process_sample(struct fir_filter_fixed *filter, int32_t sample)
+{
+	uint32_t tap_idx;
+	uint32_t coeff_idx;
+	int32_t output = 0;
+
+	if (!filter)
+		return 0;
+
+	/* Store the new data point */
+	filter->data[filter->put_idx] = sample;
+
+	coeff_idx = filter->put_idx;
+
+	/* Apply fir taps on data */
+	for (tap_idx = 0; tap_idx < filter->tap_count; tap_idx++) {
+		output += filter->data[tap_idx] * filter->coefficients[coeff_idx];
+
+		if (coeff_idx)
+			coeff_idx--;
+		else
+			coeff_idx = filter->tap_count-1;
+	}
+
+	filter->put_idx++;
+	if (filter->put_idx >= filter->tap_count)
+		filter->put_idx = 0;
+
+	return output;
+}

stm-firmware/include/reflow-controller/fir-filter.h

@@ -0,0 +1,37 @@
+/* Reflow Oven Controller
+*
+* Copyright (C) 2021  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.
+*
+* The Reflow Oven Control Firmware 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 the reflow oven controller project.
+* If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef __FIR_FILTER_H__
+#define __FIR_FILTER_H__
+
+#include <stdint.h>
+
+struct fir_filter_fixed {
+    uint32_t tap_count;
+    const int32_t *coefficients;
+    int32_t *data;
+    uint32_t put_idx;
+};
+
+void fir_filter_init_null(struct fir_filter_fixed *filter);
+
+int32_t fir_filter_process_sample(struct fir_filter_fixed *filter, int32_t sample);
+
+#endif /* __FIR_FILTER_H__ */