add missing files

buffer.h

@@ -0,0 +1,11 @@
+#include <stdint.h>
+
+#define BUFFER_SIZE 200
+
+typedef struct {
+    uint16_t values[BUFFER_SIZE];
+    uint16_t position;
+} buffer_t;
+
+void insert_to_buffer(uint16_t val, volatile buffer_t* buf);
+float get_buffer_mean(volatile buffer_t* buf);