Add FM filtering

FMDirectForm1.h

@@ -0,0 +1,114 @@
+
+/*******************************************************************************
+This header file has been taken from:
+"A Collection of Useful C++ Classes for Digital Signal Processing"
+By Vinnie Falco 
+Bernd Porr adapted it for Linux and turned it into a filter using
+fixed point arithmetic.
+--------------------------------------------------------------------------------
+License: MIT License (http://www.opensource.org/licenses/mit-license.php)
+Copyright (c) 2009 by Vinnie Falco
+Copyright (C) 2013-2017, Bernd Porr, mail@berndporr.me.uk
+Copyright (C) 2020 , Mario Molitor , mario_molitor@web.de
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*******************************************************************************/
+
+// based on https://raw.githubusercontent.com/berndporr/iir_fixed_point/master/DirectFormI.h
+
+#include "Globals.h"
+
+#ifndef DIRECTFORMI_HPP_
+#define DIRECTFORMI_HPP_
+class CFMDirectFormI
+{
+public:
+
+	// convenience function which takes the a0 argument but ignores it!
+	CFMDirectFormI(const q31_t b0, const q31_t b1, const q31_t b2,
+			const q31_t, const q31_t a1, const q31_t a2)
+	{
+		// FIR coefficients
+		c_b0 = b0;
+		c_b1 = b1;
+		c_b2 = b2;
+		// IIR coefficients
+		c_a1 = a1;
+		c_a2 = a2;
+		reset();
+	}
+
+	CFMDirectFormI(const CFMDirectFormI &my)
+	{
+	// delay line
+		m_x2 = my.m_x2; // x[n-2]
+		m_y2 = my.m_y2; // y[n-2]
+		m_x1 = my.m_x1; // x[n-1]
+		m_y1 = my.m_y1; // y[n-1]
+
+	// coefficients
+		c_b0 = my.c_b0;
+		c_b1 = my.c_b1;
+		c_b2 = my.c_b2; // FIR
+		c_a1 = my.c_a1;
+		c_a2 = my.c_a2; // IIR
+
+	// scaling factor
+		q_scaling = my.q_scaling; // 2^q_scaling
+    }
+
+	void reset ()
+	{
+		m_x1 = 0;
+		m_x2 = 0;
+		m_y1 = 0;
+		m_y2 = 0;
+	}
+
+	// filtering operation: one sample in and one out
+	inline q15_t filter(const q15_t in)
+	{
+		// calculate the output
+		register q31_t out_upscaled = c_b0 * in    //F4FXL puting stauration here made everything quiet, not sure why
+									+ c_b1 * m_x1
+									+ c_b2 * m_x2
+									- c_a1 * m_y1
+									- c_a2 * m_y2;
+
+		q15_t out = __SSAT(out_upscaled >> 15, 15);
+
+		// update the delay lines
+		m_x2 = m_x1;
+		m_y2 = m_y1;
+		m_x1 = in;
+		m_y1 = out;
+
+		return out;
+	}
+
+private:
+	// delay line
+	q31_t m_x2; // x[n-2]
+	q31_t m_y2; // y[n-2]
+	q31_t m_x1; // x[n-1]
+	q31_t m_y1; // y[n-1]
+
+	// coefficients
+	q31_t c_b0,c_b1,c_b2; // FIR
+	q31_t c_a1,c_a2; // IIR
+};
+
+#endif /* DIRECTFORMI_HPP_ */