Android - Accessing Input device "msm_pcm_in" from User space

This article shows code snippet on how to access input device driver from user space.

Recording from input device (msm_pcm_in: a char Device Driver) follows the below events

Open device :

int ret = open("/dev/msm_pcm_in", O_RDWR); // open device

struct msm_audio_config confg;

ioctl(ret, AUDIO_GET_CONFIG, &confg) // this call fill the structure with default driver values.


cfg.channel_count = 1; // assign new number of channel(1= mono, 2 = stereo)
cfg.sample_rate = 8000;// assign sampling rate such as 8000 or 16000,.....
int val = ioctl(ret, AUDIO_SET_CONFIG, &confg);// set the new audio configuration


Before we being to start audio read/write operations, create a file to store buffers
const char *fn = /sdcard/tmp/file1;
int file = open(fn, O_CREAT | O_RDWR, 0666);

bool isrecording = true; // use this flag to stop recording (true default, false to disable reading)

ioctl(ret, AUDIO_START, 0);




fcntl(0, F_SETFL, O_NONBLOCK);// provides control of open file descriptors.

unsigned char buf[4092];

for (;;) {
while (!isrecording) {
// close all file descriptors and exit
}
if (read(ret, buf,confg.buffer_size ) != confg.buffer_size) {
// if fail to read
// close all file descriptors and exit
}

if (write(file, buf, confg.buffer_size) != confg.buffer_size) {
// if fail to read
// close all file descriptors and exit
}

}



Close device:

close(ret);
...
...
close (file);


Note: To run this as a recorder app, make sure you have root privileges.