我仍然面临在嵌入式系统上使用ALSA捕获的问题。
我现在可以从库中打开设备，在使用snddevices脚本之后。但是在每次调用readi时，应用程序在大约10秒后返回错误消息Input/output error (EIO)。在尝试停止设备后，整个系统冻结，需要硬复位。
我不知道ALSA是否正确安装在系统上。启动时，会提到ALSA驱动程序。是version 1.0.18.rc3。如何测试ALSA和/或设备是否正确安装?
frame大小和period列表设置是否正确(我不太了解音频处理)，以及我是否必须使用interleaved或non-interleaved捕获，或者是否无关紧要。
#include <alsa/asoundlib.h>
const char* print_pcm_state(snd_pcm_state_t state)
{
switch(state)
{
case SND_PCM_STATE_OPEN: return("SND_PCM_STATE_OPEN");
case SND_PCM_STATE_SETUP: return("SND_PCM_STATE_SETUP");
case SND_PCM_STATE_PREPARED: return("SND_PCM_STATE_PREPARED");
case SND_PCM_STATE_RUNNING: return("SND_PCM_STATE_RUNNING");
case SND_PCM_STATE_XRUN: return("SND_PCM_STATE_XRUN");
case SND_PCM_STATE_DRAINING: return("SND_PCM_STATE_DRAINING");
case SND_PCM_STATE_PAUSED: return("SND_PCM_STATE_PAUSED");
case SND_PCM_STATE_SUSPENDED: return("SND_PCM_STATE_SUSPENDED");
case SND_PCM_STATE_DISCONNECTED: return("SND_PCM_STATE_DISCONNECTED");
}
return "UNKNOWN STATE";
}
int main(int argc, char* argv[])
{
int rc; int err;
// pcm state
snd_pcm_state_t pcm_state;
// handle
snd_pcm_t *handle;
// hardware to open
char *pcm_name;
pcm_name = strdup("hw:0,0");
// parameters
snd_pcm_hw_params_t *params;
/* Open PCM device for playback. */
rc = snd_pcm_open(&handle, pcm_name, SND_PCM_STREAM_CAPTURE, 0);
if (rc < 0)
{
printf("unable to open pcm device: %sn", snd_strerror(rc));
exit(1);
}
// Allocate a hardware parameters object.
// rc = snd_pcm_hw_params_alloca(¶ms); // original from a sample code, didn't compile?!?
rc = snd_pcm_hw_params_malloc(¶ms);
if(rc<0)
{
printf("cannot allocate hardware parameter structure (%s) ...n", snd_strerror(rc));
}
/* Fill it in with default values. */
rc = snd_pcm_hw_params_any(handle, params);
if(rc<0)
{
printf("Error: (%s) ...n", snd_strerror(rc));
}
bool interleaved = true;
// Set the desired hardware parameters.
if (interleaved)
{
// Interleaved mode
if ((rc = snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0)
{
printf("cannot set access type (%s) ...n", snd_strerror(rc));
return rc;
}
printf("access type = SND_PCM_ACCESS_RW_INTERLEAVEDn");
}
else
{
if ((rc = snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_NONINTERLEAVED)) < 0)
{
printf("cannot set access type (%s) ...n", snd_strerror(rc));
return rc;
}
printf("access type = SND_PCM_ACCESS_RW_NONINTERLEAVEDn");
}
// Signed 16-bit little-endian format
if ((rc = snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE)) < 0) {
printf("cannot set sample format (%s) ...n", snd_strerror(rc));
return 1;
}
// TODO: channel number important - will a bad channel number crash the whole capturing?
int nChannels = 2;
if ((rc = snd_pcm_hw_params_set_channels(handle, params, nChannels)) < 0) {
printf("cannot set channel count (%s) ...n", snd_strerror(rc));
return 1;
}
// TODO: right?
unsigned int wanted_rate = 22000;
unsigned int exact_rate = wanted_rate;
if ((rc = snd_pcm_hw_params_set_rate_near(handle, params, &exact_rate, 0)) < 0) {
printf("cannot set sample rate (%s) ...n", snd_strerror(rc));
return 1;
}
if (wanted_rate != exact_rate)
{
printf("The rate %i Hz is not supported by your hardware.n"
"==> Using %i Hz instead.n", wanted_rate, exact_rate);
}
// TODO: what about these parts? What are those "frames" and what are the "periods"?
// must this be set according to the hardware?!?
snd_pcm_uframes_t frames = 640;
int periods = 8;
// Set number of periods. Periods used to be called fragments.
if (snd_pcm_hw_params_set_periods(handle, params, periods, 0) < 0) {
printf("Error setting periods.n");
return 1;
}
if ((err = snd_pcm_hw_params_set_period_size_near(handle, params, &frames, 0)) < 0) {
fprintf(stderr, "Init: cannot set period_size (%s) ...n", snd_strerror(err));
return err;
}
// TODO: is this the size needed for a single read-call?
snd_pcm_uframes_t buff_size = 0;
err = snd_pcm_hw_params_get_buffer_size(params, &buff_size);
if (err < 0) {
printf("Unable to get buffer size for playback: %sn", snd_strerror(err));
return err;
}
printf("needed buffersize: %i n", (int)buff_size);
pcm_state = snd_pcm_state(handle);
printf("0.m State: %sn", print_pcm_state(pcm_state));
// what's this?
snd_pcm_sw_params_t* swparams_c;
// snd_pcm_hw_params will call PREPARE internally!
if ((err = snd_pcm_hw_params(handle, params)) < 0) {
fprintf(stderr, "Init: cannot set parameters (%s) ...n", snd_strerror(err));
return err;
}
pcm_state = snd_pcm_state(handle);
printf("0.n State: %sn", print_pcm_state(pcm_state));
printf("capturen");
// test: start device:
/*
err = snd_pcm_start(handle);
if(err < 0)
{
fprintf (stderr, "cannot start device (%s)n",
snd_strerror (err));
exit (1);
}
*/
//state
pcm_state = snd_pcm_state(handle);
printf("1. State: %sn", print_pcm_state(pcm_state));
// Is this ok?!?
//short buf[100*2048];
//short buf[5120*1024]; // seg-fault?!?
short buf[5120];
// only try to read a single time
int i=0;
for (i = 0; i < 1; ++i) {
if(interleaved)
{
if ((err = snd_pcm_readi (handle, buf, frames)) < 0)
// if ((err = snd_pcm_writei (handle, buf, 1)) < 0) // ioctl error
{
printf("EBADFD %i -> EPIPE %i -> ESTRPIPE %in",EBADFD,EPIPE,ESTRPIPE);
if(err == -EBADFD)
printf("-EBADFD: PCM is not in the right state (SND_PCM_STATE_PREPARED or SND_PCM_STATE_RUNNING) n");
if(err == -EPIPE) printf("-EPIPE: an overrun occurred n");
if(err == -ESTRPIPE) printf("-ESTRPIPE: a suspend event occurred (stream is suspended and waiting for an application recovery)n");
fprintf (stderr, "error %i : interleaved read from audio interface failed (%s)n",
err, snd_strerror (err));
pcm_state = snd_pcm_state(handle);
printf("1.1 State: %sn", print_pcm_state(pcm_state));
exit (1);
}
}
else
{
// TODO: is it hardware dependent whether I can exlusively use readi or readn?
// how does a readn call have to look like? needs multiple buffers?!?
printf("non-interleaved capture not implementedn");
//if ((err = snd_pcm_readn (handle, buf, frames)) != frames) {
// fprintf (stderr, "non-interleaved read from audio interface failed (%s)n",
// snd_strerror (err));
// exit (1);
//}
}
}
pcm_state = snd_pcm_state(handle);
printf("2. State: %sn", print_pcm_state(pcm_state));
printf("closen");
snd_pcm_close (handle);
pcm_state = snd_pcm_state(handle);
printf("3. State: %sn", print_pcm_state(pcm_state));
printf("finishn");
return 0;
}
产生以下输出:
~ # ./audioTest
access type = SND_PCM_ACCESS_RW_INTERLEAVED
The rate 22000 Hz is not supported by your hardware.
==> Using 16000 Hz instead.
needed buffersize: 5120
0.m State: SND_PCM_STATE_OPEN
hello, alsa~.
0.n State: SND_PCM_STATE_PREPARED
capture
1. State: SND_PCM_STATE_PREPARED
EBADFD 77 -> EPIPE 32 -> ESTRPIPE 86
error -5 : interleaved read from audio interface failed (Input/output error)
1.1 State: SND_PCM_STATE_RUNNING
冻结之后…
如果我在capture打印(取自参考实现)之前添加另一个参数化块:
{
snd_pcm_uframes_t boundary = 0;
snd_pcm_sw_params_alloca(&swparams_c);
/* get the current swparams */
err = snd_pcm_sw_params_current(handle, swparams_c);
if (err < 0) {
printf("Unable to determine current swparams_c: %sn", snd_strerror(err));
return err;
}
// what's this? necessary?
/*
//err = snd_pcm_sw_params_set_tstamp_mode(handle, swparams_c, SND_PCM_TSTAMP_ENABLE);
err = snd_pcm_sw_params_set_tstamp_mode(handle, swparams_c, SND_PCM_TSTAMP_MMAP);
if (err < 0) {
printf("Unable to set tstamp mode : %sn", snd_strerror(err));
return err;
}
*/
err = snd_pcm_sw_params_set_avail_min(handle, swparams_c, frames);
if (err < 0) {
printf("Unable to call snd_pcm_sw_params_set_avail_min(): %sn", snd_strerror(err));
return err;
}
err = snd_pcm_sw_params_set_start_threshold(handle, swparams_c, (buff_size / frames) * frames);
if (err < 0) {
printf("Unable to call snd_pcm_sw_params_set_start_threshold(): %sn", snd_strerror(err));
return err;
}
err = snd_pcm_sw_params_get_boundary(swparams_c, &boundary);
if (err < 0) {
printf("Unable to call snd_pcm_sw_params_get_boundary(): %sn", snd_strerror(err));
return err;
}
err = snd_pcm_sw_params_set_stop_threshold(handle, swparams_c, boundary);
if (err < 0) {
printf("Unable to call snd_pcm_sw_params_set_stop_threshold(): %sn", snd_strerror(err));
return err;
}
/* align all transfers to 1 sample */
err = snd_pcm_sw_params_set_xfer_align(handle, swparams_c, 1);
if (err < 0) {
printf("Unable to set transfer align for playback: %sn", snd_strerror(err));
return err;
}
/* write the sw parameters */
err = snd_pcm_sw_params(handle, swparams_c);
if (err < 0) {
printf("Unable to set swparams_c : %sn", snd_strerror(err));
return err;
}
}
我最终得到消息:
error -5 : interleaved read from audio interface failed (Input/output error)
2.1 State: SND_PCM_STATE_PREPARED
但没有冻结。那么，如果设备正在"运行"，为什么它会冻结呢?
有什么建议来做这个设备/代码工作吗?
对不起，所有的代码，我不确定是否需要所有的参数。如果太难读，请告诉我为了可读性，是否可以更好地封装整个init部分
第二种情况(设置软件参数)不是未定义行为，也不是BUG。它实际上是期望的行为。当state为PREPARED时，读取少于start_threshold帧会导致线程阻塞。另一个线程可以开始捕获。补丁被恢复(参见此提交):
ALSA: pcm:注释为什么pcm不运行时读取阻塞
这避免了62ba568f7aef ("ALSA: pcm:当size <在00a399cad1a0>阻止用户从另一个线程开始捕获。
第一个案例不应该有任何问题。当设置硬件参数时，ALSA使用软件参数的默认值。"start_threshold"设置为"1"。设备在第一次读取时启动。然而，似乎有另一个超时导致EIO。如果我在ALSA核心中发现问题，我会在这里发布更新。无论如何，可能是设备驱动程序没有发出中断，导致系统冻结。