diff --git a/src/hdlc.h b/src/hdlc.h
new file mode 100644
index 0000000..10ec8e2
--- /dev/null
+++ b/src/hdlc.h
@@ -0,0 +1,18 @@
+#pragma once
+
+#include <osmocom/core/bits.h>
+
+enum hdlc_proc_state {
+	STATE_INIT,
+	STATE_FLAG_WAIT_ZERO,
+	STATE_PAYLOAD,
+};
+
+struct hdlc_proc {
+	ubit_t history[8];
+	ubit_t next_outbyte[8];
+	enum hdlc_proc_state state;
+	uint8_t num_bits;
+};
+
+int process_raw_hdlc(struct hdlc_proc *hdlc, uint8_t *data, unsigned int len);