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Date: Sun, 4 Feb 2001 12:07:28 +0100
From: clock@ghost.btnet.cz
To: linux-kernel@vger.kernel.org
Subject: Inadmissible sound dropouts on 2.2.18
Reply-To: clock@atrey.karlin.mff.cuni.cz
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I found that 2.2.18 probably rudely drops samples (lets ocassionally one sample
be played several times) on the Gravis Ultrasound output device. I use 2.2.18
and the native kernel drivers. I wrote this program that should produce a clean
sine tone. Instead I hear a sine interspaced with crackling. The crackling
repeats at 100Hz I guess. There runs nothing CPU-consuming. The sound process
takes 5% CPU. It's funny Linux drops sound samples just at 5% of CPU load. I
got AMD K6-2 3D 400Mhz at 400Mhz, 4*100MHz, running stably between 20-35 deg C
of case temperature. I got PCI / AGP board FIC VA-503+.  There are three serial
ports, none of them was transceiving at that time. There is one ISA NE2000 NIC
which was not sending any packets.  There is a ISA Gravis Ultrasound PnP. Two
IDE disks, one of them sleeping, the second spinning but nod reading/writing.
64MB of 100MHz DIMM SDRAM, which runs for years without problems. 1MB L2 cache.
AGP video card ATI. No X server running, no SVGAlib application running.  No
USB peripherals.

The crackling is not dependent on the buffer size you can set up in the C code.
The crackling is dependent on the frequency of the sine. It's clearly audible
(read: annoying) at 10kHz, audible at 1kHz, inaudible at 100Hz. So I think
they are sample dropouts - the card stops playing and repeats one sample until
kernel gets the breath and whips itself up to supply next audio data.

There are no custom changes in the drivers - no buffer tweaking, nothing. The
Gravis plays modules, midules and mp3 with nearly no problems (apart from when
Loreena Mc Kennith sings too high and too loud, I hear something that looks like
MP3 frames bounds, but I can't surely tell who's responsible for this - if the
Fraunhofer Institute or Linux Kernel)

root@ghost:/usr/src/linux# cat /proc/version
Linux version 2.2.18 (root@ghost) (gcc version 2.95.2.1 19991024 (release)) #14
Mon Jan 29 15:14:27 MET 2001

Clock


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CFLAGS=-O3 -Wall -fomit-frame-pointer
LDFLAGS=-s -lm

all: syncro beat

syncro: syncro.c

beat: beat.c

clean:
	rm -f *.o core syncro beat


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Content-Disposition: attachment; filename="beat.c"

#include <string.h>
#include <sys/soundcard.h>
#include <sys/ioctl.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <math.h>

unsigned char errmsg[256];
int r;
int dsp;
int bits=16;
int channels;
int blocksize;

float left=10000;
float right=10000;
double left_angle=0;
double right_angle=0;
unsigned char buffer[65536];

void hum(void)
{
	int a;
	int val;
	int remains;
	unsigned char *ptr;

	new_buffer:
	ptr=buffer;
	for (a=0;a<sizeof(buffer)/4;a++){
		val=32767*sin(left_angle);
		*ptr++=val&255;
		*ptr++=val>>8;
		val=32767*sin(right_angle);
		*ptr++=val&255;
		*ptr++=val>>8;
		left_angle+=2*M_PI/44100*left;
		if (left_angle>=2*M_PI) left_angle-=2*M_PI;
		right_angle+=2*M_PI/44100*right;
		if (right_angle>=2*M_PI) right_angle-=2*M_PI;
	}
	remains=sizeof(buffer);
	ptr=buffer;
	a2:
	if (!remains) goto new_buffer;
	val=write(dsp,ptr,remains);
	if (val>=0){
		remains-=val;
		ptr+=val;
		goto a2;
	}
	if (errno==EAGAIN||errno==EINTR) goto a2;
	perror("beat");
	exit(1);
}

/*-------------------------------MAIN---------------------------------------*/
int main(int argc, char **argv)
{
	int a;

again:
dsp=open("/dev/dsp",O_WRONLY);
if (dsp<0){
	if (errno==EINTR||errno==EAGAIN) goto again;
}

if (r){
	fprintf(stderr,"Can't open sound device.\n");
	exit(1);
}

r=ioctl(dsp,SNDCTL_DSP_RESET,NULL);
if (r){
	fprintf(stderr,"Can't reset sound device.\n");
	exit(1);
}

a=44100;
r=ioctl(dsp,SNDCTL_DSP_SPEED,&a);
if (r){
	fprintf(stderr,"Can't set 44100.\n");
	exit(1);
}

a=1;
r=ioctl(dsp,SNDCTL_DSP_STEREO,&a);
if (r){
	fprintf(stderr,"Can't set stereo.\n");
	exit(1);
}

a=16;
r=ioctl(dsp,SOUND_PCM_WRITE_BITS,&a);
if (r){
	fprintf(stderr,"Can't set 16bit.\n");
	exit(1);
}

r=ioctl(dsp,SNDCTL_DSP_GETBLKSIZE,&blocksize);
if (r){
	fprintf(stderr,"Can't get blocksize.\n");
	exit(1);
}

r=ioctl(dsp,SNDCTL_DSP_SYNC,NULL);
if (r){
	fprintf(stderr,"Can't sync device.\n");
	exit(1);
}

hum();

return 0;
	
	printf("Error setting up driver\n");
	return 1;
}

--6TrnltStXW4iwmi0--
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