oss_mixer_user_17.4程序

/*
 *	./mixer    或 ./mixer  
 *	device可以是:vol, pcm, speaker, line, mic, cd, igain, line1, phin, video
 *	SOUND_MIXER_READ_DEVMASK
 *	SOUND_MIXER_READ_STEREODEVS
 *	iotcl(fd, SOUND_WRITE(device), &level);	--设置增益
 *
 */

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 


/* 用来存储所有可用混音设备的名称 */
const char *sound_device_names[] = SOUND_DEVICE_NAMES;

int fd;
int devmask, stereodevs;		/* 混音器信息对应的bit掩码 */
char *name;			/* 显示命令的使用方法及所有可用的混音设备 */

void usage()
{
	int i;
	fprintf(stderr, "usage: %s  \n" 
			"%s  \n\n""Where  is one of:\n", name, name);
	for(i = 0; i < SOUND_MIXER_NRDEVICES; i++)
		if((1 << i) & devmask)
			fprintf(stderr, "%s ", sound_device_names[i]);
	fprintf(stderr, "\n");
	exit(1);
}

int main(int argc, char *argv[])
{
	int left, right, level;			/* 增益设置 */
	int status;						/* 系统调用的返回值 */
	int device;						/* 选用的混音设备 */
	char *dev;						/* 混音设备的名称 */
	int i;

	name = argv[0];

	/* 以只读方式打开混音设备 */
	fd = open("/dev/mixer", O_RDONLY);
	if(-1 == fd)
	{
		perror("unalbe to open /dev/mixer");
		exit(1);
	}

	status = ioctl(fd, SOUND_MIXER_READ_DEVMASK, &devmask);
	if(-1 == status)
		perror("SOUND_MIXER_READ_DEVMASK iotcl failed");

	status = ioctl(fd, SOUND_MIXER_READ_STEREODEVS, &stereodevs);
	if(-1 == status)
		perror("SOUND_MIXER_READ_STEREODEVS ioctl failed");

	/* 检查用户输入 */
	if(argc != 3 && argc != 4)
		usage();

	/* 保存用户输入的混音器名称 */
	dev = argv[1];

	/* 确定即将用到的混音设备 */
	for(i = 0; i < SOUND_MIXER_NRDEVICES; i++)
		if((1 << i) & devmask && !strcmp(dev, sound_device_names[i]))
			break;

	if(i == SOUND_MIXER_NRDEVICES)
	{
		/* 没有找到匹配项 */
		fprintf(stderr, "%s is not a valid mixer device\n", dev);
		usage();
	}

	/* 查找到有效的混音设备 */
	device = i;

	/* 获得增益值 */
	if(4 == argc)
	{
		/* 左、右声道均给定 */
		left = atoi(argv[2]);
		right = atoi(argv[3]);
	}
	else
	{
		/* 左、右声道设为相等 */
		left = atoi(argv[2]);
		right = atoi(argv[2]);
	}

	/* 对非立体声设备给出警告信息 */
	if((left != right) && !((1 << i) & stereodevs))
	{
		fprintf(stderr, "warning: %s is not a stereo device\n", dev);
	}

	/* 将两个声道的值合到同一变量中 */
	level = (right << 8) + left;

	/* 设置增益 */
	status = ioctl(fd, MIXER_WRITE(device), &level);
	if(-1 == status)
	{
		perror("MIXER_WRITE ioctl failed");
		exit(1);
	}

	/* 获得从驱动返回的左右声道的增益 */
	left = level & 0xff;
	right = (level & 0xff00) >> 8;

	/* 显示实际设置的增益 */
	fprintf(stderr, "%s gain set to %d%% / %d%%", dev, left, right);

	/* 关闭混音设备 */
	close(fd);

	return 0;
}