Staging: add echo cancelation module

This is used by mISDN and Zaptel drivers.

From: Steve Underwood <steveu@coppice.org>
From: David Rowe <david@rowetel.com>
Cc: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/Kconfig

@@ -39,4 +39,6 @@ source "drivers/staging/winbond/Kconfig"
 
 source "drivers/staging/wlan-ng/Kconfig"
 
+source "drivers/staging/echo/Kconfig"
+
 endif # STAGING

drivers/staging/Makefile

@@ -8,3 +8,4 @@ obj-$(CONFIG_VIDEO_GO7007)	+= go7007/
 obj-$(CONFIG_USB_IP_COMMON)	+= usbip/
 obj-$(CONFIG_W35UND)		+= winbond/
 obj-$(CONFIG_PRISM2_USB)	+= wlan-ng/
+obj-$(CONFIG_ECHO)		+= echo/

drivers/staging/echo/Kconfig

+config ECHO
+	tristate "Line Echo Canceller support"
+	default n
+	---help---
+	  This driver provides line echo cancelling support for mISDN and
+	  Zaptel drivers.
+
+	  To compile this driver as a module, choose M here. The module
+	  will be called echo.

drivers/staging/echo/Makefile

+obj-$(CONFIG_ECHO) += echo.o

drivers/staging/echo/TODO

+TODO:
+	- checkpatch.pl cleanups
+	- Lindent
+	- typedef removals
+	- handle bit_operations.h (merge in or make part of common code?)
+	- remove proc interface, only use echo.h interface (proc interface is
+	  racy and not correct.)
+
+Please send patches to Greg Kroah-Hartman <greg@kroah.com> and Cc: Steve
+Underwood <steveu@coppice.org> and David Rowe <david@rowetel.com>

drivers/staging/echo/bit_operations.h

+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * bit_operations.h - Various bit level operations, such as bit reversal
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2006 Steve Underwood
+ *
+ * All rights reserved.
+ *
+ * This program 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.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id: bit_operations.h,v 1.11 2006/11/28 15:37:03 steveu Exp $
+ */
+
+/*! \file */
+
+#if !defined(_BIT_OPERATIONS_H_)
+#define _BIT_OPERATIONS_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#if defined(__i386__)  ||  defined(__x86_64__)
+/*! \brief Find the bit position of the highest set bit in a word
+    \param bits The word to be searched
+    \return The bit number of the highest set bit, or -1 if the word is zero. */
+static __inline__ int top_bit(unsigned int bits)
+{
+    int res;
+
+    __asm__ (" xorl %[res],%[res];\n"
+             " decl %[res];\n"
+             " bsrl %[bits],%[res]\n"
+             : [res] "=&r" (res)
+             : [bits] "rm" (bits));
+    return res;
+}
+/*- End of function --------------------------------------------------------*/
+
+/*! \brief Find the bit position of the lowest set bit in a word
+    \param bits The word to be searched
+    \return The bit number of the lowest set bit, or -1 if the word is zero. */
+static __inline__ int bottom_bit(unsigned int bits)
+{
+    int res;
+
+    __asm__ (" xorl %[res],%[res];\n"
+             " decl %[res];\n"
+             " bsfl %[bits],%[res]\n"
+             : [res] "=&r" (res)
+             : [bits] "rm" (bits));
+    return res;
+}
+/*- End of function --------------------------------------------------------*/
+#else
+static __inline__ int top_bit(unsigned int bits)
+{
+    int i;
+
+    if (bits == 0)
+        return -1;
+    i = 0;
+    if (bits & 0xFFFF0000)
+    {
+        bits &= 0xFFFF0000;
+        i += 16;
+    }
+    if (bits & 0xFF00FF00)
+    {
+        bits &= 0xFF00FF00;
+        i += 8;
+    }
+    if (bits & 0xF0F0F0F0)
+    {
+        bits &= 0xF0F0F0F0;
+        i += 4;
+    }
+    if (bits & 0xCCCCCCCC)
+    {
+        bits &= 0xCCCCCCCC;
+        i += 2;
+    }
+    if (bits & 0xAAAAAAAA)
+    {
+        bits &= 0xAAAAAAAA;
+        i += 1;
+    }
+    return i;
+}
+/*- End of function --------------------------------------------------------*/
+
+static __inline__ int bottom_bit(unsigned int bits)
+{
+    int i;
+
+    if (bits == 0)
+        return -1;
+    i = 32;
+    if (bits & 0x0000FFFF)
+    {
+        bits &= 0x0000FFFF;
+        i -= 16;
+    }
+    if (bits & 0x00FF00FF)
+    {
+        bits &= 0x00FF00FF;
+        i -= 8;
+    }
+    if (bits & 0x0F0F0F0F)
+    {
+        bits &= 0x0F0F0F0F;
+        i -= 4;
+    }
+    if (bits & 0x33333333)
+    {
+        bits &= 0x33333333;
+        i -= 2;
+    }
+    if (bits & 0x55555555)
+    {
+        bits &= 0x55555555;
+        i -= 1;
+    }
+    return i;
+}
+/*- End of function --------------------------------------------------------*/
+#endif
+
+/*! \brief Bit reverse a byte.
+    \param data The byte to be reversed.
+    \return The bit reversed version of data. */
+static __inline__ uint8_t bit_reverse8(uint8_t x)
+{
+#if defined(__i386__)  ||  defined(__x86_64__)
+    /* If multiply is fast */
+    return ((x*0x0802U & 0x22110U) | (x*0x8020U & 0x88440U))*0x10101U >> 16;
+#else
+    /* If multiply is slow, but we have a barrel shifter */
+    x = (x >> 4) | (x << 4);
+    x = ((x & 0xCC) >> 2) | ((x & 0x33) << 2);
+    return ((x & 0xAA) >> 1) | ((x & 0x55) << 1);
+#endif
+}
+/*- End of function --------------------------------------------------------*/
+
+/*! \brief Bit reverse a 16 bit word.
+    \param data The word to be reversed.
+    \return The bit reversed version of data. */
+uint16_t bit_reverse16(uint16_t data);
+
+/*! \brief Bit reverse a 32 bit word.
+    \param data The word to be reversed.
+    \return The bit reversed version of data. */
+uint32_t bit_reverse32(uint32_t data);
+
+/*! \brief Bit reverse each of the four bytes in a 32 bit word.
+    \param data The word to be reversed.
+    \return The bit reversed version of data. */
+uint32_t bit_reverse_4bytes(uint32_t data);
+
+/*! \brief Find the number of set bits in a 32 bit word.
+    \param x The word to be searched.
+    \return The number of set bits. */
+int one_bits32(uint32_t x);
+
+/*! \brief Create a mask as wide as the number in a 32 bit word.
+    \param x The word to be searched.
+    \return The mask. */
+uint32_t make_mask32(uint32_t x);
+
+/*! \brief Create a mask as wide as the number in a 16 bit word.
+    \param x The word to be searched.
+    \return The mask. */
+uint16_t make_mask16(uint16_t x);
+
+/*! \brief Find the least significant one in a word, and return a word
+           with just that bit set.
+    \param x The word to be searched.
+    \return The word with the single set bit. */
+static __inline__ uint32_t least_significant_one32(uint32_t x)
+{
+    return (x & (-(int32_t) x));
+}
+/*- End of function --------------------------------------------------------*/
+
+/*! \brief Find the most significant one in a word, and return a word
+           with just that bit set.
+    \param x The word to be searched.
+    \return The word with the single set bit. */
+static __inline__ uint32_t most_significant_one32(uint32_t x)
+{
+#if defined(__i386__)  ||  defined(__x86_64__)
+    return 1 << top_bit(x);
+#else
+    x = make_mask32(x);
+    return (x ^ (x >> 1));
+#endif
+}
+/*- End of function --------------------------------------------------------*/
+
+/*! \brief Find the parity of a byte.
+    \param x The byte to be checked.
+    \return 1 for odd, or 0 for even. */
+static __inline__ int parity8(uint8_t x)
+{
+    x = (x ^ (x >> 4)) & 0x0F;
+    return (0x6996 >> x) & 1;
+}
+/*- End of function --------------------------------------------------------*/
+
+/*! \brief Find the parity of a 16 bit word.
+    \param x The word to be checked.
+    \return 1 for odd, or 0 for even. */
+static __inline__ int parity16(uint16_t x)
+{
+    x ^= (x >> 8);
+    x = (x ^ (x >> 4)) & 0x0F;
+    return (0x6996 >> x) & 1;
+}
+/*- End of function --------------------------------------------------------*/
+
+/*! \brief Find the parity of a 32 bit word.
+    \param x The word to be checked.
+    \return 1 for odd, or 0 for even. */
+static __inline__ int parity32(uint32_t x)
+{
+    x ^= (x >> 16);
+    x ^= (x >> 8);
+    x = (x ^ (x >> 4)) & 0x0F;
+    return (0x6996 >> x) & 1;
+}
+/*- End of function --------------------------------------------------------*/
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/

drivers/staging/echo/echo.h

+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * echo.c - A line echo canceller.  This code is being developed
+ *          against and partially complies with G168.
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *         and David Rowe <david_at_rowetel_dot_com>
+ *
+ * Copyright (C) 2001 Steve Underwood and 2007 David Rowe
+ *
+ * All rights reserved.
+ *
+ * This program 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.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id: echo.h,v 1.9 2006/10/24 13:45:28 steveu Exp $
+ */
+
+#ifndef __ECHO_H
+#define __ECHO_H
+
+/*! \page echo_can_page Line echo cancellation for voice
+
+\section echo_can_page_sec_1 What does it do?
+This module aims to provide G.168-2002 compliant echo cancellation, to remove
+electrical echoes (e.g. from 2-4 wire hybrids) from voice calls.
+
+\section echo_can_page_sec_2 How does it work?
+The heart of the echo cancellor is FIR filter. This is adapted to match the
+echo impulse response of the telephone line. It must be long enough to
+adequately cover the duration of that impulse response. The signal transmitted
+to the telephone line is passed through the FIR filter. Once the FIR is
+properly adapted, the resulting output is an estimate of the echo signal
+received from the line. This is subtracted from the received signal. The result
+is an estimate of the signal which originated at the far end of the line, free
+from echos of our own transmitted signal.
+
+The least mean squares (LMS) algorithm is attributed to Widrow and Hoff, and
+was introduced in 1960. It is the commonest form of filter adaption used in
+things like modem line equalisers and line echo cancellers. There it works very
+well.  However, it only works well for signals of constant amplitude. It works
+very poorly for things like speech echo cancellation, where the signal level
+varies widely.  This is quite easy to fix. If the signal level is normalised -
+similar to applying AGC - LMS can work as well for a signal of varying
+amplitude as it does for a modem signal. This normalised least mean squares
+(NLMS) algorithm is the commonest one used for speech echo cancellation. Many
+other algorithms exist - e.g. RLS (essentially the same as Kalman filtering),
+FAP, etc. Some perform significantly better than NLMS.  However, factors such
+as computational complexity and patents favour the use of NLMS.
+
+A simple refinement to NLMS can improve its performance with speech. NLMS tends
+to adapt best to the strongest parts of a signal. If the signal is white noise,
+the NLMS algorithm works very well. However, speech has more low frequency than
+high frequency content. Pre-whitening (i.e. filtering the signal to flatten its
+spectrum) the echo signal improves the adapt rate for speech, and ensures the
+final residual signal is not heavily biased towards high frequencies. A very
+low complexity filter is adequate for this, so pre-whitening adds little to the
+compute requirements of the echo canceller.
+
+An FIR filter adapted using pre-whitened NLMS performs well, provided certain
+conditions are met:
+
+    - The transmitted signal has poor self-correlation.
+    - There is no signal being generated within the environment being
+      cancelled.
+
+The difficulty is that neither of these can be guaranteed.
+
+If the adaption is performed while transmitting noise (or something fairly
+noise like, such as voice) the adaption works very well. If the adaption is
+performed while transmitting something highly correlative (typically narrow
+band energy such as signalling tones or DTMF), the adaption can go seriously
+wrong. The reason is there is only one solution for the adaption on a near
+random signal - the impulse response of the line. For a repetitive signal,
+there are any number of solutions which converge the adaption, and nothing
+guides the adaption to choose the generalised one. Allowing an untrained
+canceller to converge on this kind of narrowband energy probably a good thing,
+since at least it cancels the tones. Allowing a well converged canceller to
+continue converging on such energy is just a way to ruin its generalised
+adaption. A narrowband detector is needed, so adapation can be suspended at
+appropriate times.
+
+The adaption process is based on trying to eliminate the received signal. When
+there is any signal from within the environment being cancelled it may upset
+the adaption process. Similarly, if the signal we are transmitting is small,
+noise may dominate and disturb the adaption process. If we can ensure that the
+adaption is only performed when we are transmitting a significant signal level,
+and the environment is not, things will be OK. Clearly, it is easy to tell when
+we are sending a significant signal. Telling, if the environment is generating
+a significant signal, and doing it with sufficient speed that the adaption will
+not have diverged too much more we stop it, is a little harder.
+
+The key problem in detecting when the environment is sourcing significant
+energy is that we must do this very quickly. Given a reasonably long sample of
+the received signal, there are a number of strategies which may be used to
+assess whether that signal contains a strong far end component. However, by the
+time that assessment is complete the far end signal will have already caused
+major mis-convergence in the adaption process. An assessment algorithm is
+needed which produces a fairly accurate result from a very short burst of far
+end energy.
+
+\section echo_can_page_sec_3 How do I use it?
+The echo cancellor processes both the transmit and receive streams sample by
+sample. The processing function is not declared inline. Unfortunately,
+cancellation requires many operations per sample, so the call overhead is only
+a minor burden.
+*/
+
+#include "fir.h"
+
+/* Mask bits for the adaption mode */
+#define ECHO_CAN_USE_ADAPTION	0x01
+#define ECHO_CAN_USE_NLP	0x02
+#define ECHO_CAN_USE_CNG	0x04
+#define ECHO_CAN_USE_CLIP	0x08
+#define ECHO_CAN_USE_TX_HPF	0x10
+#define ECHO_CAN_USE_RX_HPF	0x20
+#define ECHO_CAN_DISABLE	0x40
+
+/*!
+    G.168 echo canceller descriptor. This defines the working state for a line
+    echo canceller.
+*/
+typedef struct
+{
+	int16_t tx,rx;
+	int16_t clean;
+	int16_t clean_nlp;
+
+	int nonupdate_dwell;
+	int curr_pos;
+	int taps;
+	int log2taps;
+	int adaption_mode;
+
+	int cond_met;
+	int32_t Pstates;
+	int16_t adapt;
+	int32_t factor;
+	int16_t shift;
+
+	/* Average levels and averaging filter states */
+	int Ltxacc, Lrxacc, Lcleanacc, Lclean_bgacc;
+	int Ltx, Lrx;
+	int Lclean;
+	int Lclean_bg;
+	int Lbgn, Lbgn_acc, Lbgn_upper, Lbgn_upper_acc;
+
+	/* foreground and background filter states */
+	fir16_state_t fir_state;
+	fir16_state_t fir_state_bg;
+	int16_t *fir_taps16[2];
+
+	/* DC blocking filter states */
+	int tx_1, tx_2, rx_1, rx_2;
+
+	/* optional High Pass Filter states */
+	int32_t xvtx[5], yvtx[5];
+	int32_t xvrx[5], yvrx[5];
+
+	/* Parameters for the optional Hoth noise generator */
+	int cng_level;
+	int cng_rndnum;
+	int cng_filter;
+
+	/* snapshot sample of coeffs used for development */
+	int16_t *snapshot;
+} echo_can_state_t;
+
+/*! Create a voice echo canceller context.
+    \param len The length of the canceller, in samples.
+    \return The new canceller context, or NULL if the canceller could not be created.
+*/
+echo_can_state_t *echo_can_create(int len, int adaption_mode);
+
+/*! Free a voice echo canceller context.
+    \param ec The echo canceller context.
+*/
+void echo_can_free(echo_can_state_t *ec);
+
+/*! Flush (reinitialise) a voice echo canceller context.
+    \param ec The echo canceller context.
+*/
+void echo_can_flush(echo_can_state_t *ec);
+
+/*! Set the adaption mode of a voice echo canceller context.
+    \param ec The echo canceller context.
+    \param adapt The mode.
+*/
+void echo_can_adaption_mode(echo_can_state_t *ec, int adaption_mode);
+
+void echo_can_snapshot(echo_can_state_t *ec);
+
+/*! Process a sample through a voice echo canceller.
+    \param ec The echo canceller context.
+    \param tx The transmitted audio sample.
+    \param rx The received audio sample.
+    \return The clean (echo cancelled) received sample.
+*/
+int16_t echo_can_update(echo_can_state_t *ec, int16_t tx, int16_t rx);
+
+/*! Process to high pass filter the tx signal.
+    \param ec The echo canceller context.
+    \param tx The transmitted auio sample.
+    \return The HP filtered transmit sample, send this to your D/A.
+*/
+int16_t echo_can_hpf_tx(echo_can_state_t *ec, int16_t tx);
+
+#endif	/* __ECHO_H */