Hi all ALSA experts,

I am seeing a weird behavior of ALSA API lib 1.0.23, i.e., when I use SND_PCM_FORMAT_S32_LE, I am seeing that the data format is still configured as SND_PCM_FORMAT_S16_LE and passed to kernel driver layer.

The code I am using is shown below:

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snd_pcm_t *capture_handle;

rc = snd_pcm_open(&capture_handle, devName, SND_PCM_STREAM_CAPTURE, 0 /*SND_PCM_NONBLOCK*/); /* */

if (rc < 0) { fprintf(stderr, "unable to open pcm device: %s\n", snd_strerror(rc)); exit(1); }

/* Allocate a hardware parameters object. */ snd_pcm_hw_params_malloc(&hw_params);

/* Fill it in with default values. */ snd_pcm_hw_params_any(capture_handle, hw_params);

/* Set the desired hardware parameters. */ /* Interleaved mode 2-channel*/ snd_pcm_hw_params_set_access(capture_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED); /* each frame left->right->left->right */

/* Signed 32-bit little-endian format */ snd_pcm_hw_params_set_format(capture_handle, hw_params, SND_PCM_FORMAT_S32_LE); //snd_pcm_hw_params_set_format(HANDLE(direction), hw_params, SND_PCM_FORMAT_S16_LE);

/* Two channels (stereo) */ if( (rc=snd_pcm_hw_params_set_channels(capture_handle, hw_params, 2))<0) { fprintf(stderr, "cannot set channel count 2\n"); exit(1); }

int sample_rate = rate; /* The sample rate is 50000 */ snd_pcm_hw_params_set_rate_near(capture_handle, hw_params, &sample_rate, &dir); if (sample_rate != rate) { fprintf(stderr, "The rate %d Hz is not supported by your hardware.\n ==> Using %d Hz instead.\n", rate, sample_rate); }

frames = 32; /* Set period size to 32 frames. */ snd_pcm_hw_params_set_period_size_near(capture_handle, hw_params, &frames, &dir);

int periods = 2; /* Number of periods */ snd_pcm_uframes_t buffersize = periods*frames; /* Periodsize (bytes) */

/* Set buffer size (in frames). The resulting latency is given by */ /* latency = periodsize * periods / (rate * bytes_per_frame) */ if (snd_pcm_hw_params_set_buffer_size(capture_handle, hw_params, buffersize) < 0) { /* 2 period as buffer size*/ fprintf(stderr, "Error setting buffersize.\n"); return(-1); }

/* Write the parameters to the driver */ rc = snd_pcm_hw_params(capture_handle, hw_params); /* call into kernel snd_pcm_common_ioctl1 */ if (rc < 0) { fprintf(stderr, "unable to set hw parameters: %s\n", snd_strerror(rc)); exit(1); }

Unsigned long buffer[1024];

memset(buffer, 0x0, sizeof(buffer)); /* Pre-set the data */

/* Start data transmission now */ /* Returns the number of frames actually written. */ snd_pcm_prepare(capture_handle); /* Need this if there are too many printf lines to interrupt the process */

/* Start receiving data from FPGA now */ /* Returns the number of frames actually read. */ rc = snd_pcm_readi(handle, buffer, frames);

The data read back looks like 0x????0000, which only has half content of 32-bit format.

Is there anything wrong with my code?

Any help will be appreciated.