动态库调用snd_pcm_hw_params_get_rate失败

问题

自己做了一个动态库，调用snd_pcm_hw_params_get_rate，返回总是0，但是其实是配置成功的。

通过gdb发现当动态链接时，调用堆栈如下

Breakpoint 1, init () at test.c:104
104         snd_pcm_hw_params_get_rate(params, &actualSampleRate, NULL);
(gdb) p &actualSampleRate
$4 = (unsigned int *) 0x7ffffff29c
(gdb) s
__old_snd_pcm_hw_params_get_rate (params=0x7ffffff010, dir=0x7ffffff29c) at pcm.c:7747
7747    __OLD_GET1(snd_pcm_hw_params_get_rate, unsigned int, int);
(gdb) s
__snd_pcm_hw_params_get_rate (params=0x7ffffff010, [email protected]=0x7ffffff00c, dir=0x7ffffff29c) at pcm.c:4542
4542            return snd_pcm_hw_param_get(params, SND_PCM_HW_PARAM_RATE, val, dir);

而静态链接，调用堆栈如下：

Breakpoint 1, init () at test.c:104
104         snd_pcm_hw_params_get_rate(params, &actualSampleRate, NULL);
(gdb) p &actualSampleRate
$1 = (unsigned int *) 0x7ffffff29c
(gdb) s
__snd_pcm_hw_params_get_rate (params=0x7ffffff010, val=0x7ffffff29c, dir=0x0) at pcm.c:4542
4542            return snd_pcm_hw_param_get(params, SND_PCM_HW_PARAM_RATE, val, dir);

__old_snd_pcm_hw_params_get_rate 只能接收2个参数，val是一个内部变量，从而导致返回值错误，但是为什么动态链接和静态链接调用堆栈不同还不清楚

解决办法

目前想到的就是不用这些接口，即__OLD_GET，__OLD_GET1，__OLD_NEAR，__OLD_NEAR1修饰的接口都不用，包括官网的例子也没用这样的接口，如下：

/*
 *  This small demo sends a simple sinusoidal wave to your speakers.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sched.h>
#include <errno.h>
#include <getopt.h>
#include "../include/asoundlib.h"
#include <sys/time.h>
#include <math.h>
static char *device = "plughw:0,0";         /* playback device */
static snd_pcm_format_t format = SND_PCM_FORMAT_S16;    /* sample format */
static unsigned int rate = 44100;           /* stream rate */
static unsigned int channels = 1;           /* count of channels */
static unsigned int buffer_time = 500000;       /* ring buffer length in us */
static unsigned int period_time = 100000;       /* period time in us */
static double freq = 440;               /* sinusoidal wave frequency in Hz */
static int verbose = 0;                 /* verbose flag */
static int resample = 1;                /* enable alsa-lib resampling */
static int period_event = 0;                /* produce poll event after each period */
static snd_pcm_sframes_t buffer_size;
static snd_pcm_sframes_t period_size;
static snd_output_t *output = NULL;
static void generate_sine(const snd_pcm_channel_area_t *areas, 
              snd_pcm_uframes_t offset,
              int count, double *_phase)
{
    static double max_phase = 2. * M_PI;
    double phase = *_phase;
    double step = max_phase*freq/(double)rate;
    unsigned char *samples[channels];
    int steps[channels];
    unsigned int chn;
    int format_bits = snd_pcm_format_width(format);
    unsigned int maxval = (1 << (format_bits - 1)) - 1;
    int bps = format_bits / 8;  /* bytes per sample */
    int phys_bps = snd_pcm_format_physical_width(format) / 8;
    int big_endian = snd_pcm_format_big_endian(format) == 1;
    int to_unsigned = snd_pcm_format_unsigned(format) == 1;
    int is_float = (format == SND_PCM_FORMAT_FLOAT_LE ||
            format == SND_PCM_FORMAT_FLOAT_BE);
    /* verify and prepare the contents of areas */
    for (chn = 0; chn < channels; chn++) {
        if ((areas[chn].first % 8) != 0) {
            printf("areas[%u].first == %u, aborting...\n", chn, areas[chn].first);
            exit(EXIT_FAILURE);
        }
        samples[chn] = /*(signed short *)*/(((unsigned char *)areas[chn].addr) + (areas[chn].first / 8));
        if ((areas[chn].step % 16) != 0) {
            printf("areas[%u].step == %u, aborting...\n", chn, areas[chn].step);
            exit(EXIT_FAILURE);
        }
        steps[chn] = areas[chn].step / 8;
        samples[chn] += offset * steps[chn];
    }
    /* fill the channel areas */
    while (count-- > 0) {
        union {
            float f;
            int i;
        } fval;
        int res, i;
        if (is_float) {
            fval.f = sin(phase);
            res = fval.i;
        } else
            res = sin(phase) * maxval;
        if (to_unsigned)
            res ^= 1U << (format_bits - 1);
        for (chn = 0; chn < channels; chn++) {
            /* Generate data in native endian format */
            if (big_endian) {
                for (i = 0; i < bps; i++)
                    *(samples[chn] + phys_bps - 1 - i) = (res >> i * 8) & 0xff;
            } else {
                for (i = 0; i < bps; i++)
                    *(samples[chn] + i) = (res >>  i * 8) & 0xff;
            }
            samples[chn] += steps[chn];
        }
        phase += step;
        if (phase >= max_phase)
            phase -= max_phase;
    }
    *_phase = phase;
}
static int set_hwparams(snd_pcm_t *handle,
            snd_pcm_hw_params_t *params,
            snd_pcm_access_t access)
{
    unsigned int rrate;
    snd_pcm_uframes_t size;
    int err, dir;
    /* choose all parameters */
    err = snd_pcm_hw_params_any(handle, params);
    if (err < 0) {
        printf("Broken configuration for playback: no configurations available: %s\n", snd_strerror(err));
        return err;
    }
    /* set hardware resampling */
    err = snd_pcm_hw_params_set_rate_resample(handle, params, resample);
    if (err < 0) {
        printf("Resampling setup failed for playback: %s\n", snd_strerror(err));
        return err;
    }
    /* set the interleaved read/write format */
    err = snd_pcm_hw_params_set_access(handle, params, access);
    if (err < 0) {
        printf("Access type not available for playback: %s\n", snd_strerror(err));
        return err;
    }
    /* set the sample format */
    err = snd_pcm_hw_params_set_format(handle, params, format);
    if (err < 0) {
        printf("Sample format not available for playback: %s\n", snd_strerror(err));
        return err;
    }
    /* set the count of channels */
    err = snd_pcm_hw_params_set_channels(handle, params, channels);
    if (err < 0) {
        printf("Channels count (%u) not available for playbacks: %s\n", channels, snd_strerror(err));
        return err;
    }
    /* set the stream rate */
    rrate = rate;
    err = snd_pcm_hw_params_set_rate_near(handle, params, &rrate, 0);
    if (err < 0) {
        printf("Rate %uHz not available for playback: %s\n", rate, snd_strerror(err));
        return err;
    }
    if (rrate != rate) {
        printf("Rate doesn't match (requested %uHz, get %iHz)\n", rate, err);
        return -EINVAL;
    }
    /* set the buffer time */
    err = snd_pcm_hw_params_set_buffer_time_near(handle, params, &buffer_time, &dir);
    if (err < 0) {
        printf("Unable to set buffer time %u for playback: %s\n", buffer_time, snd_strerror(err));
        return err;
    }
    err = snd_pcm_hw_params_get_buffer_size(params, &size);
    if (err < 0) {
        printf("Unable to get buffer size for playback: %s\n", snd_strerror(err));
        return err;
    }
    buffer_size = size;
    /* set the period time */
    err = snd_pcm_hw_params_set_period_time_near(handle, params, &period_time, &dir);
    if (err < 0) {
        printf("Unable to set period time %u for playback: %s\n", period_time, snd_strerror(err));
        return err;
    }
    err = snd_pcm_hw_params_get_period_size(params, &size, &dir);
    if (err < 0) {
        printf("Unable to get period size for playback: %s\n", snd_strerror(err));
        return err;
    }
    period_size = size;
    /* write the parameters to device */
    err = snd_pcm_hw_params(handle, params);
    if (err < 0) {
        printf("Unable to set hw params for playback: %s\n", snd_strerror(err));
        return err;
    }
    return 0;
}
static int set_swparams(snd_pcm_t *handle, snd_pcm_sw_params_t *swparams)
{
    int err;
    /* get the current swparams */
    err = snd_pcm_sw_params_current(handle, swparams);
    if (err < 0) {
        printf("Unable to determine current swparams for playback: %s\n", snd_strerror(err));
        return err;
    }
    /* start the transfer when the buffer is almost full: */
    /* (buffer_size / avail_min) * avail_min */
    err = snd_pcm_sw_params_set_start_threshold(handle, swparams, (buffer_size / period_size) * period_size);
    if (err < 0) {
        printf("Unable to set start threshold mode for playback: %s\n", snd_strerror(err));
        return err;
    }
    /* allow the transfer when at least period_size samples can be processed */
    /* or disable this mechanism when period event is enabled (aka interrupt like style processing) */
    err = snd_pcm_sw_params_set_avail_min(handle, swparams, period_event ? buffer_size : period_size);
    if (err < 0) {
        printf("Unable to set avail min for playback: %s\n", snd_strerror(err));
        return err;
    }
    /* enable period events when requested */
    if (period_event) {
        err = snd_pcm_sw_params_set_period_event(handle, swparams, 1);
        if (err < 0) {
            printf("Unable to set period event: %s\n", snd_strerror(err));
            return err;
        }
    }
    /* write the parameters to the playback device */
    err = snd_pcm_sw_params(handle, swparams);
    if (err < 0) {
        printf("Unable to set sw params for playback: %s\n", snd_strerror(err));
        return err;
    }
    return 0;
}
/*
 *   Underrun and suspend recovery
 */
 
static int xrun_recovery(snd_pcm_t *handle, int err)
{
    if (verbose)
        printf("stream recovery\n");
    if (err == -EPIPE) {    /* under-run */
        err = snd_pcm_prepare(handle);
        if (err < 0)
            printf("Can't recovery from underrun, prepare failed: %s\n", snd_strerror(err));
        return 0;
    } else if (err == -ESTRPIPE) {
        while ((err = snd_pcm_resume(handle)) == -EAGAIN)
            sleep(1);   /* wait until the suspend flag is released */
        if (err < 0) {
            err = snd_pcm_prepare(handle);
            if (err < 0)
                printf("Can't recovery from suspend, prepare failed: %s\n", snd_strerror(err));
        }
        return 0;
    }
    return err;
}
/*
 *   Transfer method - write only
 */
static int write_loop(snd_pcm_t *handle,
              signed short *samples,
              snd_pcm_channel_area_t *areas)
{
    double phase = 0;
    signed short *ptr;
    int err, cptr;
    while (1) {
        generate_sine(areas, 0, period_size, &phase);
        ptr = samples;
        cptr = period_size;
        while (cptr > 0) {
            err = snd_pcm_writei(handle, ptr, cptr);
            if (err == -EAGAIN)
                continue;
            if (err < 0) {
                if (xrun_recovery(handle, err) < 0) {
                    printf("Write error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
                break;  /* skip one period */
            }
            ptr += err * channels;
            cptr -= err;
        }
    }
}
 
/*
 *   Transfer method - write and wait for room in buffer using poll
 */
static int wait_for_poll(snd_pcm_t *handle, struct pollfd *ufds, unsigned int count)
{
    unsigned short revents;
    while (1) {
        poll(ufds, count, -1);
        snd_pcm_poll_descriptors_revents(handle, ufds, count, &revents);
        if (revents & POLLERR)
            return -EIO;
        if (revents & POLLOUT)
            return 0;
    }
}
static int write_and_poll_loop(snd_pcm_t *handle,
                   signed short *samples,
                   snd_pcm_channel_area_t *areas)
{
    struct pollfd *ufds;
    double phase = 0;
    signed short *ptr;
    int err, count, cptr, init;
    count = snd_pcm_poll_descriptors_count (handle);
    if (count <= 0) {
        printf("Invalid poll descriptors count\n");
        return count;
    }
    ufds = malloc(sizeof(struct pollfd) * count);
    if (ufds == NULL) {
        printf("No enough memory\n");
        return -ENOMEM;
    }
    if ((err = snd_pcm_poll_descriptors(handle, ufds, count)) < 0) {
        printf("Unable to obtain poll descriptors for playback: %s\n", snd_strerror(err));
        return err;
    }
    init = 1;
    while (1) {
        if (!init) {
            err = wait_for_poll(handle, ufds, count);
            if (err < 0) {
                if (snd_pcm_state(handle) == SND_PCM_STATE_XRUN ||
                    snd_pcm_state(handle) == SND_PCM_STATE_SUSPENDED) {
                    err = snd_pcm_state(handle) == SND_PCM_STATE_XRUN ? -EPIPE : -ESTRPIPE;
                    if (xrun_recovery(handle, err) < 0) {
                        printf("Write error: %s\n", snd_strerror(err));
                        exit(EXIT_FAILURE);
                    }
                    init = 1;
                } else {
                    printf("Wait for poll failed\n");
                    return err;
                }
            }
        }
        generate_sine(areas, 0, period_size, &phase);
        ptr = samples;
        cptr = period_size;
        while (cptr > 0) {
            err = snd_pcm_writei(handle, ptr, cptr);
            if (err < 0) {
                if (xrun_recovery(handle, err) < 0) {
                    printf("Write error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
                init = 1;
                break;  /* skip one period */
            }
            if (snd_pcm_state(handle) == SND_PCM_STATE_RUNNING)
                init = 0;
            ptr += err * channels;
            cptr -= err;
            if (cptr == 0)
                break;
            /* it is possible, that the initial buffer cannot store */
            /* all data from the last period, so wait awhile */
            err = wait_for_poll(handle, ufds, count);
            if (err < 0) {
                if (snd_pcm_state(handle) == SND_PCM_STATE_XRUN ||
                    snd_pcm_state(handle) == SND_PCM_STATE_SUSPENDED) {
                    err = snd_pcm_state(handle) == SND_PCM_STATE_XRUN ? -EPIPE : -ESTRPIPE;
                    if (xrun_recovery(handle, err) < 0) {
                        printf("Write error: %s\n", snd_strerror(err));
                        exit(EXIT_FAILURE);
                    }
                    init = 1;
                } else {
                    printf("Wait for poll failed\n");
                    return err;
                }
            }
        }
    }
}
/*
 *   Transfer method - asynchronous notification
 */
struct async_private_data {
    signed short *samples;
    snd_pcm_channel_area_t *areas;
    double phase;
};
static void async_callback(snd_async_handler_t *ahandler)
{
    snd_pcm_t *handle = snd_async_handler_get_pcm(ahandler);
    struct async_private_data *data = snd_async_handler_get_callback_private(ahandler);
    signed short *samples = data->samples;
    snd_pcm_channel_area_t *areas = data->areas;
    snd_pcm_sframes_t avail;
    int err;
    
    avail = snd_pcm_avail_update(handle);
    while (avail >= period_size) {
        generate_sine(areas, 0, period_size, &data->phase);
        err = snd_pcm_writei(handle, samples, period_size);
        if (err < 0) {
            printf("Write error: %s\n", snd_strerror(err));
            exit(EXIT_FAILURE);
        }
        if (err != period_size) {
            printf("Write error: written %i expected %li\n", err, period_size);
            exit(EXIT_FAILURE);
        }
        avail = snd_pcm_avail_update(handle);
    }
}
static int async_loop(snd_pcm_t *handle,
              signed short *samples,
              snd_pcm_channel_area_t *areas)
{
    struct async_private_data data;
    snd_async_handler_t *ahandler;
    int err, count;
    data.samples = samples;
    data.areas = areas;
    data.phase = 0;
    err = snd_async_add_pcm_handler(&ahandler, handle, async_callback, &data);
    if (err < 0) {
        printf("Unable to register async handler\n");
        exit(EXIT_FAILURE);
    }
    for (count = 0; count < 2; count++) {
        generate_sine(areas, 0, period_size, &data.phase);
        err = snd_pcm_writei(handle, samples, period_size);
        if (err < 0) {
            printf("Initial write error: %s\n", snd_strerror(err));
            exit(EXIT_FAILURE);
        }
        if (err != period_size) {
            printf("Initial write error: written %i expected %li\n", err, period_size);
            exit(EXIT_FAILURE);
        }
    }
    if (snd_pcm_state(handle) == SND_PCM_STATE_PREPARED) {
        err = snd_pcm_start(handle);
        if (err < 0) {
            printf("Start error: %s\n", snd_strerror(err));
            exit(EXIT_FAILURE);
        }
    }
    /* because all other work is done in the signal handler,
       suspend the process */
    while (1) {
        sleep(1);
    }
}
/*
 *   Transfer method - asynchronous notification + direct write
 */
static void async_direct_callback(snd_async_handler_t *ahandler)
{
    snd_pcm_t *handle = snd_async_handler_get_pcm(ahandler);
    struct async_private_data *data = snd_async_handler_get_callback_private(ahandler);
    const snd_pcm_channel_area_t *my_areas;
    snd_pcm_uframes_t offset, frames, size;
    snd_pcm_sframes_t avail, commitres;
    snd_pcm_state_t state;
    int first = 0, err;
    
    while (1) {
        state = snd_pcm_state(handle);
        if (state == SND_PCM_STATE_XRUN) {
            err = xrun_recovery(handle, -EPIPE);
            if (err < 0) {
                printf("XRUN recovery failed: %s\n", snd_strerror(err));
                exit(EXIT_FAILURE);
            }
            first = 1;
        } else if (state == SND_PCM_STATE_SUSPENDED) {
            err = xrun_recovery(handle, -ESTRPIPE);
            if (err < 0) {
                printf("SUSPEND recovery failed: %s\n", snd_strerror(err));
                exit(EXIT_FAILURE);
            }
        }
        avail = snd_pcm_avail_update(handle);
        if (avail < 0) {
            err = xrun_recovery(handle, avail);
            if (err < 0) {
                printf("avail update failed: %s\n", snd_strerror(err));
                exit(EXIT_FAILURE);
            }
            first = 1;
            continue;
        }
        if (avail < period_size) {
            if (first) {
                first = 0;
                err = snd_pcm_start(handle);
                if (err < 0) {
                    printf("Start error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
            } else {
                break;
            }
            continue;
        }
        size = period_size;
        while (size > 0) {
            frames = size;
            err = snd_pcm_mmap_begin(handle, &my_areas, &offset, &frames);
            if (err < 0) {
                if ((err = xrun_recovery(handle, err)) < 0) {
                    printf("MMAP begin avail error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
                first = 1;
            }
            generate_sine(my_areas, offset, frames, &data->phase);
            commitres = snd_pcm_mmap_commit(handle, offset, frames);
            if (commitres < 0 || (snd_pcm_uframes_t)commitres != frames) {
                if ((err = xrun_recovery(handle, commitres >= 0 ? -EPIPE : commitres)) < 0) {
                    printf("MMAP commit error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
                first = 1;
            }
            size -= frames;
        }
    }
}
static int async_direct_loop(snd_pcm_t *handle,
                 signed short *samples ATTRIBUTE_UNUSED,
                 snd_pcm_channel_area_t *areas ATTRIBUTE_UNUSED)
{
    struct async_private_data data;
    snd_async_handler_t *ahandler;
    const snd_pcm_channel_area_t *my_areas;
    snd_pcm_uframes_t offset, frames, size;
    snd_pcm_sframes_t commitres;
    int err, count;
    data.samples = NULL;    /* we do not require the global sample area for direct write */
    data.areas = NULL;  /* we do not require the global areas for direct write */
    data.phase = 0;
    err = snd_async_add_pcm_handler(&ahandler, handle, async_direct_callback, &data);
    if (err < 0) {
        printf("Unable to register async handler\n");
        exit(EXIT_FAILURE);
    }
    for (count = 0; count < 2; count++) {
        size = period_size;
        while (size > 0) {
            frames = size;
            err = snd_pcm_mmap_begin(handle, &my_areas, &offset, &frames);
            if (err < 0) {
                if ((err = xrun_recovery(handle, err)) < 0) {
                    printf("MMAP begin avail error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
            }
            generate_sine(my_areas, offset, frames, &data.phase);
            commitres = snd_pcm_mmap_commit(handle, offset, frames);
            if (commitres < 0 || (snd_pcm_uframes_t)commitres != frames) {
                if ((err = xrun_recovery(handle, commitres >= 0 ? -EPIPE : commitres)) < 0) {
                    printf("MMAP commit error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
            }
            size -= frames;
        }
    }
    err = snd_pcm_start(handle);
    if (err < 0) {
        printf("Start error: %s\n", snd_strerror(err));
        exit(EXIT_FAILURE);
    }
    /* because all other work is done in the signal handler,
       suspend the process */
    while (1) {
        sleep(1);
    }
}
/*
 *   Transfer method - direct write only
 */
static int direct_loop(snd_pcm_t *handle,
               signed short *samples ATTRIBUTE_UNUSED,
               snd_pcm_channel_area_t *areas ATTRIBUTE_UNUSED)
{
    double phase = 0;
    const snd_pcm_channel_area_t *my_areas;
    snd_pcm_uframes_t offset, frames, size;
    snd_pcm_sframes_t avail, commitres;
    snd_pcm_state_t state;
    int err, first = 1;
    while (1) {
        state = snd_pcm_state(handle);
        if (state == SND_PCM_STATE_XRUN) {
            err = xrun_recovery(handle, -EPIPE);
            if (err < 0) {
                printf("XRUN recovery failed: %s\n", snd_strerror(err));
                return err;
            }
            first = 1;
        } else if (state == SND_PCM_STATE_SUSPENDED) {
            err = xrun_recovery(handle, -ESTRPIPE);
            if (err < 0) {
                printf("SUSPEND recovery failed: %s\n", snd_strerror(err));
                return err;
            }
        }
        avail = snd_pcm_avail_update(handle);
        if (avail < 0) {
            err = xrun_recovery(handle, avail);
            if (err < 0) {
                printf("avail update failed: %s\n", snd_strerror(err));
                return err;
            }
            first = 1;
            continue;
        }
        if (avail < period_size) {
            if (first) {
                first = 0;
                err = snd_pcm_start(handle);
                if (err < 0) {
                    printf("Start error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
            } else {
                err = snd_pcm_wait(handle, -1);
                if (err < 0) {
                    if ((err = xrun_recovery(handle, err)) < 0) {
                        printf("snd_pcm_wait error: %s\n", snd_strerror(err));
                        exit(EXIT_FAILURE);
                    }
                    first = 1;
                }
            }
            continue;
        }
        size = period_size;
        while (size > 0) {
            frames = size;
            err = snd_pcm_mmap_begin(handle, &my_areas, &offset, &frames);
            if (err < 0) {
                if ((err = xrun_recovery(handle, err)) < 0) {
                    printf("MMAP begin avail error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
                first = 1;
            }
            generate_sine(my_areas, offset, frames, &phase);
            commitres = snd_pcm_mmap_commit(handle, offset, frames);
            if (commitres < 0 || (snd_pcm_uframes_t)commitres != frames) {
                if ((err = xrun_recovery(handle, commitres >= 0 ? -EPIPE : commitres)) < 0) {
                    printf("MMAP commit error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
                first = 1;
            }
            size -= frames;
        }
    }
}
 
/*
 *   Transfer method - direct write only using mmap_write functions
 */
static int direct_write_loop(snd_pcm_t *handle,
                 signed short *samples,
                 snd_pcm_channel_area_t *areas)
{
    double phase = 0;
    signed short *ptr;
    int err, cptr;
    while (1) {
        generate_sine(areas, 0, period_size, &phase);
        ptr = samples;
        cptr = period_size;
        while (cptr > 0) {
            err = snd_pcm_mmap_writei(handle, ptr, cptr);
            if (err == -EAGAIN)
                continue;
            if (err < 0) {
                if (xrun_recovery(handle, err) < 0) {
                    printf("Write error: %s\n", snd_strerror(err));
                    exit(EXIT_FAILURE);
                }
                break;  /* skip one period */
            }
            ptr += err * channels;
            cptr -= err;
        }
    }
}
 
/*
 *
 */
struct transfer_method {
    const char *name;
    snd_pcm_access_t access;
    int (*transfer_loop)(snd_pcm_t *handle,
                 signed short *samples,
                 snd_pcm_channel_area_t *areas);
};
static struct transfer_method transfer_methods[] = {
    { "write", SND_PCM_ACCESS_RW_INTERLEAVED, write_loop },
    { "write_and_poll", SND_PCM_ACCESS_RW_INTERLEAVED, write_and_poll_loop },
    { "async", SND_PCM_ACCESS_RW_INTERLEAVED, async_loop },
    { "async_direct", SND_PCM_ACCESS_MMAP_INTERLEAVED, async_direct_loop },
    { "direct_interleaved", SND_PCM_ACCESS_MMAP_INTERLEAVED, direct_loop },
    { "direct_noninterleaved", SND_PCM_ACCESS_MMAP_NONINTERLEAVED, direct_loop },
    { "direct_write", SND_PCM_ACCESS_MMAP_INTERLEAVED, direct_write_loop },
    { NULL, SND_PCM_ACCESS_RW_INTERLEAVED, NULL }
};
static void help(void)
{
    int k;
    printf(
"Usage: pcm [OPTION]... [FILE]...\n"
"-h,--help  help\n"
"-D,--device    playback device\n"
"-r,--rate  stream rate in Hz\n"
"-c,--channels  count of channels in stream\n"
"-f,--frequency sine wave frequency in Hz\n"
"-b,--buffer    ring buffer size in us\n"
"-p,--period    period size in us\n"
"-m,--method    transfer method\n"
"-o,--format    sample format\n"
"-v,--verbose   show the PCM setup parameters\n"
"-n,--noresample  do not resample\n"
"-e,--pevent    enable poll event after each period\n"
"\n");
        printf("Recognized sample formats are:");
        for (k = 0; k < SND_PCM_FORMAT_LAST; ++k) {
                const char *s = snd_pcm_format_name(k);
                if (s)
                        printf(" %s", s);
        }
        printf("\n");
        printf("Recognized transfer methods are:");
        for (k = 0; transfer_methods[k].name; k++)
            printf(" %s", transfer_methods[k].name);
    printf("\n");
}
int main(int argc, char *argv[])
{
    struct option long_option[] =
    {
        {"help", 0, NULL, 'h'},
        {"device", 1, NULL, 'D'},
        {"rate", 1, NULL, 'r'},
        {"channels", 1, NULL, 'c'},
        {"frequency", 1, NULL, 'f'},
        {"buffer", 1, NULL, 'b'},
        {"period", 1, NULL, 'p'},
        {"method", 1, NULL, 'm'},
        {"format", 1, NULL, 'o'},
        {"verbose", 1, NULL, 'v'},
        {"noresample", 1, NULL, 'n'},
        {"pevent", 1, NULL, 'e'},
        {NULL, 0, NULL, 0},
    };
    snd_pcm_t *handle;
    int err, morehelp;
    snd_pcm_hw_params_t *hwparams;
    snd_pcm_sw_params_t *swparams;
    int method = 0;
    signed short *samples;
    unsigned int chn;
    snd_pcm_channel_area_t *areas;
    snd_pcm_hw_params_alloca(&hwparams);
    snd_pcm_sw_params_alloca(&swparams);
    morehelp = 0;
    while (1) {
        int c;
        if ((c = getopt_long(argc, argv, "hD:r:c:f:b:p:m:o:vne", long_option, NULL)) < 0)
            break;
        switch (c) {
        case 'h':
            morehelp++;
            break;
        case 'D':
            device = strdup(optarg);
            break;
        case 'r':
            rate = atoi(optarg);
            rate = rate < 4000 ? 4000 : rate;
            rate = rate > 196000 ? 196000 : rate;
            break;
        case 'c':
            channels = atoi(optarg);
            channels = channels < 1 ? 1 : channels;
            channels = channels > 1024 ? 1024 : channels;
            break;
        case 'f':
            freq = atoi(optarg);
            freq = freq < 50 ? 50 : freq;
            freq = freq > 5000 ? 5000 : freq;
            break;
        case 'b':
            buffer_time = atoi(optarg);
            buffer_time = buffer_time < 1000 ? 1000 : buffer_time;
            buffer_time = buffer_time > 1000000 ? 1000000 : buffer_time;
            break;
        case 'p':
            period_time = atoi(optarg);
            period_time = period_time < 1000 ? 1000 : period_time;
            period_time = period_time > 1000000 ? 1000000 : period_time;
            break;
        case 'm':
            for (method = 0; transfer_methods[method].name; method++)
                    if (!strcasecmp(transfer_methods[method].name, optarg))
                    break;
            if (transfer_methods[method].name == NULL)
                method = 0;
            break;
        case 'o':
            for (format = 0; format < SND_PCM_FORMAT_LAST; format++) {
                const char *format_name = snd_pcm_format_name(format);
                if (format_name)
                    if (!strcasecmp(format_name, optarg))
                    break;
            }
            if (format == SND_PCM_FORMAT_LAST)
                format = SND_PCM_FORMAT_S16;
            if (!snd_pcm_format_linear(format) &&
                !(format == SND_PCM_FORMAT_FLOAT_LE ||
                  format == SND_PCM_FORMAT_FLOAT_BE)) {
                printf("Invalid (non-linear/float) format %s\n",
                       optarg);
                return 1;
            }
            break;
        case 'v':
            verbose = 1;
            break;
        case 'n':
            resample = 0;
            break;
        case 'e':
            period_event = 1;
            break;
        }
    }
    if (morehelp) {
        help();
        return 0;
    }
    err = snd_output_stdio_attach(&output, stdout, 0);
    if (err < 0) {
        printf("Output failed: %s\n", snd_strerror(err));
        return 0;
    }
    printf("Playback device is %s\n", device);
    printf("Stream parameters are %uHz, %s, %u channels\n", rate, snd_pcm_format_name(format), channels);
    printf("Sine wave rate is %.4fHz\n", freq);
    printf("Using transfer method: %s\n", transfer_methods[method].name);
    if ((err = snd_pcm_open(&handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
        printf("Playback open error: %s\n", snd_strerror(err));
        return 0;
    }
    
    if ((err = set_hwparams(handle, hwparams, transfer_methods[method].access)) < 0) {
        printf("Setting of hwparams failed: %s\n", snd_strerror(err));
        exit(EXIT_FAILURE);
    }
    if ((err = set_swparams(handle, swparams)) < 0) {
        printf("Setting of swparams failed: %s\n", snd_strerror(err));
        exit(EXIT_FAILURE);
    }
    if (verbose > 0)
        snd_pcm_dump(handle, output);
    samples = malloc((period_size * channels * snd_pcm_format_physical_width(format)) / 8);
    if (samples == NULL) {
        printf("No enough memory\n");
        exit(EXIT_FAILURE);
    }
    
    areas = calloc(channels, sizeof(snd_pcm_channel_area_t));
    if (areas == NULL) {
        printf("No enough memory\n");
        exit(EXIT_FAILURE);
    }
    for (chn = 0; chn < channels; chn++) {
        areas[chn].addr = samples;
        areas[chn].first = chn * snd_pcm_format_physical_width(format);
        areas[chn].step = channels * snd_pcm_format_physical_width(format);
    }
    err = transfer_methods[method].transfer_loop(handle, samples, areas);
    if (err < 0)
        printf("Transfer failed: %s\n", snd_strerror(err));
    free(areas);
    free(samples);
    snd_pcm_close(handle);
    return 0;
}