我仍然面临在嵌入式系统上使用ALSA捕获的问题。
使用snddevices脚本后，我现在可以从库中打开设备。但是，对于每次调用，应用程序在大约10秒的时间后在Input/output error个调用上返回错误消息EIO（readi）。
在尝试停止设备后，整个系统冻结并需要硬重置。
我无法判断ALSA是否在系统上正确安装。在启动时，提到了ALSA驱动程序。它是version 1.0.18.rc3。如何测试ALSA和/或设备是否安装正确？
这是我的测试代码，请告诉我内部是否有错误。我不确定frame尺寸和period是否设置正确（我不太了解音频处理）以及是否必须使用interleaved或non-interleaved捕获或是否无关紧要。
#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: %s\n", 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_INTERLEAVED\n");
}
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_NONINTERLEAVED\n");
}
// 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: %s\n", snd_strerror(err));
return err;
}
printf("needed buffersize: %i \n", (int)buff_size);
pcm_state = snd_pcm_state(handle);
printf("0.m State: %s\n", 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: %s\n", print_pcm_state(pcm_state));
printf("capture\n");
// 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: %s\n", 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 %i\n",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: %s\n", 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 implemented\n");
//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: %s\n", print_pcm_state(pcm_state));
printf("close\n");
snd_pcm_close (handle);
pcm_state = snd_pcm_state(handle);
printf("3. State: %s\n", print_pcm_state(pcm_state));
printf("finish\n");
return 0;
}
产生这个输出：
~ # ./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
之后冻结......
如果我在capture打印之前添加另一个参数化块（取自参考实现）：
{
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: %s\n", 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 : %s\n", 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(): %s\n", 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(): %s\n", 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(): %s\n", 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(): %s\n", 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: %s\n", 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 : %s\n", snd_strerror(err));
return err;
}
}
我最终收到了消息：
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，如果设备运行＆＃34;？
，为什么它会冻结呢？有什么建议让这个设备/代码有效吗？
对于所有代码，很抱歉，我不确定是否需要所有参数。如果难以阅读，请告诉我是否可能更好地封装整个init部分以便于阅读。
答案 0 :(得分：1)
第二种情况（设置软件参数）会导致状态为PREPARED且您读取少于start_threshold帧时出现不确定的行为。实际上发生的是等待例程中的超时导致EIO错误。这或多或少是一个BUG。我已发送了patch来解决此问题。
第一种情况应该没有问题。设置硬件参数后，ALSA会为软件参数设置默认值。 start_threshold设置为1。该设备在首次读取时启动。但是，似乎还有另一个超时导致EIO。如果发现ALSA核心存在问题，我将对此进行调查并在此处发布更新。无论如何，可能不是设备驱动程序发出了中断并导致系统死机。