Re: [Bluez-devel] AGC and anti-noise patch for btsco kernel module

[Andreas Beck <becka-bzdvl@bedatec.de>]

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Andreas Beck <becka-bzdvl@bedatec.de> wrote:
> He's right. Depending on how the problem is created, my fix is actually
> flawed anyway, though it will mask the problem quite well.
> I'll think about a better swapping fix. Maybe I can make the stuff
> nicer to understand as well.

[x] Done. New patch attached. Smaller, more readable and more correct.

There is one catch, though, that I hadn't noticed before:

If you turn on loopback and AGC together, chances are, that the headset
will go into a feedback loop, emitting an unpleasant beep.

This is a generic problem of loopback, which is only emphasized by the
AGC, as it will (by its design) tune up input gain until it gets a
significant signal. 

Feedback loop beep will occur, if total gain of the loop is >1.
Actually the behaviour of the beep shows, that the AGC is working
fine, as the beep will not go to full scale due to the AGC tuning 
down gain until the total gain is about 1.


However I don't see much use for loopback mode anyway, and both are
controllable in the mixer, so I don't think it will be much of a
problem. If you need loopback, keep your fingers off AGC, or tune the 
parameters so that even max gain (COMPRESSION_MAX_16) will not
trigger a feedback loop.


CU, Andy

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Index: btsco.c
===================================================================
RCS file: /cvsroot/bluetooth-alsa/btsco/kernel/btsco.c,v
retrieving revision 1.6
diff -u -r1.6 btsco.c
--- btsco.c	19 Mar 2005 14:28:59 -0000	1.6
+++ btsco.c	23 Aug 2005 15:53:07 -0000
@@ -21,6 +21,26 @@
  *
  */
 
+
+/* note: defining these two independently is not tested, 
+ * thus not recommended
+ */
+
+/* enable dynamic compression */
+#define DYNAMIC_COMPRESSION
+/* enable automatic endianness fixup */
+#define AUTO_FIXUP_BYTESHIFT
+
+
+#ifdef DYNAMIC_COMPRESSION
+/* Autoadjust mic at most this often in 1/8000s */
+#define GRABSAMPLES 400
+/* Maximum push for the mike 16= 1:1 - default 20:1 = 320 */
+#define COMPRESSION_MAX_16 320
+/* Minimum push for the mike  1= 1:16 */
+#define COMPRESSION_MIN_16 1
+#endif
+
 #define chip_t snd_card_bt_sco_t
 
 #include <sound/driver.h>
@@ -93,8 +113,15 @@
 	snd_card_t *card;
 	spinlock_t mixer_lock;
 	int mixer_volume[MIXER_ADDR_LAST + 1];
-	snd_kcontrol_t *mixer_controls[MIXER_ADDR_LAST + 2];	/* also loopback */
+#ifdef DYNAMIC_COMPRESSION
+	snd_kcontrol_t *mixer_controls[MIXER_ADDR_LAST + 2 + 1];	/* also loopback and agc */
+#else
+	snd_kcontrol_t *mixer_controls[MIXER_ADDR_LAST + 2 ];	/* also loopback */
+#endif
 	volatile int loopback;
+#ifdef DYNAMIC_COMPRESSION
+	volatile int agc;
+#endif
 	atomic_t playback_count, capture_count;
 	volatile int count_changed;
 	spinlock_t count_changed_lock;
@@ -569,6 +596,37 @@
 	return changed;
 }
 
+#ifdef DYNAMIC_COMPRESSION
+static int snd_bt_sco_agc_get(snd_kcontrol_t * kcontrol,
+				   snd_ctl_elem_value_t * ucontrol)
+{
+	snd_card_bt_sco_t *bt_sco = snd_kcontrol_chip(kcontrol);
+	unsigned long flags;
+
+	spin_lock_irqsave(&bt_sco->mixer_lock, flags);
+	ucontrol->value.integer.value[0] = bt_sco->agc;
+	spin_unlock_irqrestore(&bt_sco->mixer_lock, flags);
+	return 0;
+}
+
+static int snd_bt_sco_agc_put(snd_kcontrol_t * kcontrol,
+				   snd_ctl_elem_value_t * ucontrol)
+{
+	snd_card_bt_sco_t *bt_sco = snd_kcontrol_chip(kcontrol);
+	unsigned long flags;
+	int changed;
+	int agc;
+
+	agc = !!ucontrol->value.integer.value[0];
+
+	spin_lock_irqsave(&bt_sco->mixer_lock, flags);
+	changed = bt_sco->agc != agc;
+	bt_sco->agc = agc;
+	spin_unlock_irqrestore(&bt_sco->mixer_lock, flags);
+	return changed;
+}
+#endif
+
 #define BT_SCO_CONTROLS (sizeof(snd_bt_sco_controls)/sizeof(snd_kcontrol_new_t))
 
 static snd_kcontrol_new_t snd_bt_sco_controls[] = {
@@ -581,6 +639,16 @@
 	 .get = snd_bt_sco_loopback_get,
 	 .put = snd_bt_sco_loopback_put,
 	 }
+#ifdef DYNAMIC_COMPRESSION
+	,
+	{.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	 .name = "AGC Switch",
+	 .index = 0,
+	 .info = snd_bt_sco_boolean_info,
+	 .get = snd_bt_sco_agc_get,
+	 .put = snd_bt_sco_agc_put,
+	 }
+#endif
 };
 
 int __init snd_card_bt_sco_new_mixer(snd_card_bt_sco_t * bt_sco)
@@ -790,6 +858,18 @@
 	struct msghdr msg;
 	struct iovec iov;
 	sigset_t unblocked;
+#if defined(DYNAMIC_COMPRESSION) || defined(AUTO_FIXUP_BYTESHIFT)
+	int i;
+#endif
+#ifdef DYNAMIC_COMPRESSION
+	static int factor=16;
+	static int maxvalsmoothed=0;
+	static int maxvalgrablen=GRABSAMPLES; /* adjust volume at most 4 times/second */
+#endif
+#ifdef AUTO_FIXUP_BYTESHIFT
+	static int shift=0;
+	static unsigned char lastbyte;
+#endif
 
 	lock_kernel();
 
@@ -839,6 +919,85 @@
 		len = sock_recvmsg(sock, &msg, BUF_SIZE, 0);
 		if (len > 0) {
 
+#if defined (AUTO_FIXUP_BYTESHIFT) || defined (DYNAMIC_COMPRESSION)
+
+#ifdef AUTO_FIXUP_BYTESHIFT
+			int lostatcnt=0;
+#endif
+			if (len&1) dprintk("odd len %d\n",len);
+#ifdef AUTO_FIXUP_BYTESHIFT
+			if (shift) {
+				unsigned char newlastbyte;
+				newlastbyte=buf[len-1];
+				memmove(buf+1,buf,len-1);
+				buf[0]=lastbyte;
+				lastbyte=newlastbyte;
+			}
+#endif
+			for(i=0;i<len-1;i+=2) {
+				short int j;
+				int k;
+				j=(buf[i+1]<<8)|buf[i];
+
+#ifdef AUTO_FIXUP_BYTESHIFT    
+				/* occasionally the Headset will loose a byte
+				 * on startup. Thus kind of swapping lo/hi.
+				 * counting, if _all_ lo bytes (which are 
+				 * actually high bytes) are 0 or -1
+				 * will detect this with a very high probability
+				 */
+				if ((j&0xff)==0||(j&0xff)==0xff) {
+					lostatcnt++;
+				}
+#endif
+#ifdef DYNAMIC_COMPRESSION
+				/* scale the mic input - we do some kind
+				 * of dynamics compression
+				 */
+				k=((int)j*factor)/16;
+
+				/* clip overshoot. Better than just letting
+				 * it wrap around. Immediately adjust factor.
+				 */
+				if (k>0x7fff) {
+					k=0x7fff;
+					if (bt_sco->agc&&factor>COMPRESSION_MIN_16) factor--;
+				} else if (k<-0x8000) {
+					k=0x8000;
+					if (bt_sco->agc&&factor>COMPRESSION_MIN_16) factor--;
+				}
+				buf[i+1]=(k>>8)&0xff;
+				buf[i  ]=k&0xff;
+
+				/* find the highest absolute value in a 
+				 * GRABSAMPLES long interval.
+				 */
+				if (k<0) k=-j;
+				if (k>maxvalsmoothed) maxvalsmoothed=k;
+				/* if the interval is over, recalculate
+				 * the compression factor. Move it slowly.
+				 */
+				if (maxvalgrablen--<=0) {
+					maxvalgrablen=GRABSAMPLES;
+					/* If the noise goes up over 1000, we stop
+					 * pushing the software gain 
+					 */
+					if (maxvalsmoothed<1000&&factor<COMPRESSION_MAX_16) {
+						factor++;
+						// dprintk("Up to %d\n",factor);
+					}
+					if (!bt_sco->agc) factor=16;
+					maxvalsmoothed=0;
+				}
+#endif
+			}
+#ifdef AUTO_FIXUP_BYTESHIFT
+			if (lostatcnt==len/2&&len>32) {
+				shift=!shift;
+				dprintk("Shift problem detected! Fixing to %d.\n",shift);
+			}
+#endif
+#endif /* any of them */
 			down(&bt_sco->capture_sem);
 			if (bt_sco->capture) {
 				snd_card_bt_sco_pcm_receive