Add FIR filter code

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__ */