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pcm_iec958.c

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/**
 * \file pcm/pcm_iec958.c
 * \ingroup PCM_Plugins
 * \brief PCM IEC958 Subframe Conversion Plugin Interface
 * \author Takashi Iwai <tiwai@suse.de>
 * \date 2004
 */
/*
 *  PCM - IEC958 Subframe Conversion Plugin
 *  Copyright (c) 2004 by Takashi Iwai <tiwai@suse.de>
 *
 *
 *   This library is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Lesser General Public License as
 *   published by the Free Software Foundation; either version 2.1 of
 *   the License, or (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 *
 */
  
#include <byteswap.h>
#include "pcm_local.h"
#include "pcm_plugin.h"

#ifndef PIC
/* entry for static linking */
const char *_snd_module_pcm_iec958 = "";
#endif

/*
 */

#ifndef DOC_HIDDEN

typedef struct snd_pcm_iec958 snd_pcm_iec958_t;

typedef void (*iec958_f)(snd_pcm_iec958_t *iec,
                   const snd_pcm_channel_area_t *dst_areas,
                   snd_pcm_uframes_t dst_offset,
                   const snd_pcm_channel_area_t *src_areas,
                   snd_pcm_uframes_t src_offset,
                   unsigned int channels, snd_pcm_uframes_t frames);

00052 struct snd_pcm_iec958 {
      /* This field need to be the first */
      snd_pcm_plugin_t plug;
      unsigned int getput_idx;
      iec958_f func;
      snd_pcm_format_t sformat;
      snd_pcm_format_t format;
      unsigned int counter;
      unsigned char status[24];
      unsigned int byteswap;
      unsigned char preamble[3];    /* B/M/W or Z/X/Y */
};

enum { PREAMBLE_Z, PREAMBLE_X, PREAMBLE_Y };

#endif /* DOC_HIDDEN */

/*
 * Determine parity for time slots 4 upto 30
 * to be sure that bit 4 upt 31 will carry
 * an even number of ones and zeros.
 */
static unsigned int iec958_parity(unsigned int data)
{
      unsigned int parity;
      int bit;

      data >>= 4;     /* start from bit 4 */
      parity = 0;
      for (bit = 4; bit <= 30; bit++) {
            if (data & 1)
                  parity++;
            data >>= 1;
      }
      return (parity & 1);
}

/*
 * Compose 32bit IEC958 subframe, two sub frames
 * build one frame with two channels.
 *
 * bit 0-3  = preamble
 *     4-7  = AUX (=0)
 *     8-27 = data (12-27 for 16bit, 8-27 for 20bit, and 24bit without AUX)
 *     28   = validity (0 for valid data, else 'in error')
 *     29   = user data (0)
 *     30   = channel status (24 bytes for 192 frames)
 *     31   = parity
 */

static inline u_int32_t iec958_subframe(snd_pcm_iec958_t *iec, u_int32_t data, int channel)
{
      unsigned int byte = iec->counter >> 3;
      unsigned int mask = 1 << (iec->counter - (byte << 3));

      /* bit 4-27 */
      data >>= 4;
      data &= ~0xf;

      /* set IEC status bits (up to 192 bits) */
      if (iec->status[byte] & mask)
            data |= 0x40000000;

      if (iec958_parity(data))      /* parity bit 4-30 */
            data |= 0x80000000;

      /* Preamble */
      if (! iec->counter)
            data |= iec->preamble[PREAMBLE_Z];  /* Block start, 'Z' */
      else if (! channel)
            data |= iec->preamble[PREAMBLE_Y];  /* odd sub frame, 'Y' */
      else
            data |= iec->preamble[PREAMBLE_X];  /* even sub frame, 'X' */

      if (iec->byteswap)
            data = bswap_32(data);

      return data;
}

static inline int32_t iec958_to_s32(snd_pcm_iec958_t *iec, u_int32_t data)
{
      if (iec->byteswap)
            data = bswap_32(data);
      data &= ~0xf;
      data <<= 4;
      return (int32_t)data;
}

#ifndef DOC_HIDDEN
static void snd_pcm_iec958_decode(snd_pcm_iec958_t *iec,
                          const snd_pcm_channel_area_t *dst_areas,
                          snd_pcm_uframes_t dst_offset,
                          const snd_pcm_channel_area_t *src_areas,
                          snd_pcm_uframes_t src_offset,
                          unsigned int channels, snd_pcm_uframes_t frames)
{
#define PUT32_LABELS
#include "plugin_ops.h"
#undef PUT32_LABELS
      void *put = put32_labels[iec->getput_idx];
      unsigned int channel;
      for (channel = 0; channel < channels; ++channel) {
            const u_int32_t *src;
            char *dst;
            int src_step, dst_step;
            snd_pcm_uframes_t frames1;
            const snd_pcm_channel_area_t *src_area = &src_areas[channel];
            const snd_pcm_channel_area_t *dst_area = &dst_areas[channel];
            src = snd_pcm_channel_area_addr(src_area, src_offset);
            dst = snd_pcm_channel_area_addr(dst_area, dst_offset);
            src_step = snd_pcm_channel_area_step(src_area) / sizeof(u_int32_t);
            dst_step = snd_pcm_channel_area_step(dst_area);
            frames1 = frames;
            while (frames1-- > 0) {
                  int32_t sample = iec958_to_s32(iec, *src);
                  goto *put;
#define PUT32_END after
#include "plugin_ops.h"
#undef PUT32_END
            after:
                  src += src_step;
                  dst += dst_step;
            }
      }
}

static void snd_pcm_iec958_encode(snd_pcm_iec958_t *iec,
                          const snd_pcm_channel_area_t *dst_areas,
                          snd_pcm_uframes_t dst_offset,
                          const snd_pcm_channel_area_t *src_areas,
                          snd_pcm_uframes_t src_offset,
                          unsigned int channels, snd_pcm_uframes_t frames)
{
#define GET32_LABELS
#include "plugin_ops.h"
#undef GET32_LABELS
      void *get = get32_labels[iec->getput_idx];
      unsigned int channel;
      int32_t sample = 0;
      int counter = iec->counter;
      for (channel = 0; channel < channels; ++channel) {
            const char *src;
            u_int32_t *dst;
            int src_step, dst_step;
            snd_pcm_uframes_t frames1;
            const snd_pcm_channel_area_t *src_area = &src_areas[channel];
            const snd_pcm_channel_area_t *dst_area = &dst_areas[channel];
            src = snd_pcm_channel_area_addr(src_area, src_offset);
            dst = snd_pcm_channel_area_addr(dst_area, dst_offset);
            src_step = snd_pcm_channel_area_step(src_area);
            dst_step = snd_pcm_channel_area_step(dst_area) / sizeof(u_int32_t);
            frames1 = frames;
            iec->counter = counter;
            while (frames1-- > 0) {
                  goto *get;
#define GET32_END after
#include "plugin_ops.h"
#undef GET32_END
            after:
                  sample = iec958_subframe(iec, sample, channel);
                  // fprintf(stderr, "%d:%08x\n", frames1, sample);
                  *dst = sample;
                  src += src_step;
                  dst += dst_step;
                  iec->counter++;
                  iec->counter %= 192;
            }
      }
}
#endif /* DOC_HIDDEN */

static int snd_pcm_iec958_hw_refine_cprepare(snd_pcm_t *pcm, snd_pcm_hw_params_t *params)
{
      snd_pcm_iec958_t *iec = pcm->private_data;
      int err;
      snd_pcm_access_mask_t access_mask = { SND_PCM_ACCBIT_SHM };
      err = _snd_pcm_hw_param_set_mask(params, SND_PCM_HW_PARAM_ACCESS,
                               &access_mask);
      if (err < 0)
            return err;
      if (iec->sformat == SND_PCM_FORMAT_IEC958_SUBFRAME_LE ||
          iec->sformat == SND_PCM_FORMAT_IEC958_SUBFRAME_BE) {
            snd_pcm_format_mask_t format_mask = { SND_PCM_FMTBIT_LINEAR };
            err = _snd_pcm_hw_param_set_mask(params, SND_PCM_HW_PARAM_FORMAT,
                                     &format_mask);
      } else {
            snd_pcm_format_mask_t format_mask = {
                  { (1U << SND_PCM_FORMAT_IEC958_SUBFRAME_LE) |
                    (1U << SND_PCM_FORMAT_IEC958_SUBFRAME_BE) }
            };
            err = _snd_pcm_hw_param_set_mask(params, SND_PCM_HW_PARAM_FORMAT,
                                     &format_mask);
      }
      if (err < 0)
            return err;
      err = _snd_pcm_hw_params_set_subformat(params, SND_PCM_SUBFORMAT_STD);
      if (err < 0)
            return err;
      params->info &= ~(SND_PCM_INFO_MMAP | SND_PCM_INFO_MMAP_VALID);
      return 0;
}

static int snd_pcm_iec958_hw_refine_sprepare(snd_pcm_t *pcm, snd_pcm_hw_params_t *sparams)
{
      snd_pcm_iec958_t *iec = pcm->private_data;
      snd_pcm_access_mask_t saccess_mask = { SND_PCM_ACCBIT_MMAP };
      _snd_pcm_hw_params_any(sparams);
      _snd_pcm_hw_param_set_mask(sparams, SND_PCM_HW_PARAM_ACCESS,
                           &saccess_mask);
      _snd_pcm_hw_params_set_format(sparams, iec->sformat);
      _snd_pcm_hw_params_set_subformat(sparams, SND_PCM_SUBFORMAT_STD);
      return 0;
}

static int snd_pcm_iec958_hw_refine_schange(snd_pcm_t *pcm ATTRIBUTE_UNUSED, snd_pcm_hw_params_t *params,
                                  snd_pcm_hw_params_t *sparams)
{
      int err;
      unsigned int links = (SND_PCM_HW_PARBIT_CHANNELS |
                        SND_PCM_HW_PARBIT_RATE |
                        SND_PCM_HW_PARBIT_PERIOD_SIZE |
                        SND_PCM_HW_PARBIT_BUFFER_SIZE |
                        SND_PCM_HW_PARBIT_PERIODS |
                        SND_PCM_HW_PARBIT_PERIOD_TIME |
                        SND_PCM_HW_PARBIT_BUFFER_TIME |
                        SND_PCM_HW_PARBIT_TICK_TIME);
      err = _snd_pcm_hw_params_refine(sparams, links, params);
      if (err < 0)
            return err;
      return 0;
}
      
static int snd_pcm_iec958_hw_refine_cchange(snd_pcm_t *pcm ATTRIBUTE_UNUSED, snd_pcm_hw_params_t *params,
                                  snd_pcm_hw_params_t *sparams)
{
      int err;
      unsigned int links = (SND_PCM_HW_PARBIT_CHANNELS |
                        SND_PCM_HW_PARBIT_RATE |
                        SND_PCM_HW_PARBIT_PERIOD_SIZE |
                        SND_PCM_HW_PARBIT_BUFFER_SIZE |
                        SND_PCM_HW_PARBIT_PERIODS |
                        SND_PCM_HW_PARBIT_PERIOD_TIME |
                        SND_PCM_HW_PARBIT_BUFFER_TIME |
                        SND_PCM_HW_PARBIT_TICK_TIME);
      err = _snd_pcm_hw_params_refine(params, links, sparams);
      if (err < 0)
            return err;
      return 0;
}

static int snd_pcm_iec958_hw_refine(snd_pcm_t *pcm, snd_pcm_hw_params_t *params)
{
      return snd_pcm_hw_refine_slave(pcm, params,
                               snd_pcm_iec958_hw_refine_cprepare,
                               snd_pcm_iec958_hw_refine_cchange,
                               snd_pcm_iec958_hw_refine_sprepare,
                               snd_pcm_iec958_hw_refine_schange,
                               snd_pcm_generic_hw_refine);
}

static int snd_pcm_iec958_hw_params(snd_pcm_t *pcm, snd_pcm_hw_params_t * params)
{
      snd_pcm_iec958_t *iec = pcm->private_data;
      snd_pcm_format_t format;
      int err = snd_pcm_hw_params_slave(pcm, params,
                                snd_pcm_iec958_hw_refine_cchange,
                                snd_pcm_iec958_hw_refine_sprepare,
                                snd_pcm_iec958_hw_refine_schange,
                                snd_pcm_generic_hw_params);
      if (err < 0)
            return err;

      err = INTERNAL(snd_pcm_hw_params_get_format)(params, &format);
      if (err < 0)
            return err;

      iec->format = format;
      if (pcm->stream == SND_PCM_STREAM_PLAYBACK) {
            if (iec->sformat == SND_PCM_FORMAT_IEC958_SUBFRAME_LE ||
                iec->sformat == SND_PCM_FORMAT_IEC958_SUBFRAME_BE) {
                  iec->getput_idx = snd_pcm_linear_get_index(format, SND_PCM_FORMAT_S32);
                  iec->func = snd_pcm_iec958_encode;
                  iec->byteswap = iec->sformat != SND_PCM_FORMAT_IEC958_SUBFRAME;
            } else {
                  iec->getput_idx = snd_pcm_linear_put_index(SND_PCM_FORMAT_S32, iec->sformat);
                  iec->func = snd_pcm_iec958_decode;
                  iec->byteswap = format != SND_PCM_FORMAT_IEC958_SUBFRAME;
            }
      } else {
            if (iec->sformat == SND_PCM_FORMAT_IEC958_SUBFRAME_LE ||
                iec->sformat == SND_PCM_FORMAT_IEC958_SUBFRAME_BE) {
                  iec->getput_idx = snd_pcm_linear_put_index(SND_PCM_FORMAT_S32, format);
                  iec->func = snd_pcm_iec958_decode;
                  iec->byteswap = iec->sformat != SND_PCM_FORMAT_IEC958_SUBFRAME;
            } else {
                  iec->getput_idx = snd_pcm_linear_get_index(iec->sformat, SND_PCM_FORMAT_S32);
                  iec->func = snd_pcm_iec958_encode;
                  iec->byteswap = format != SND_PCM_FORMAT_IEC958_SUBFRAME;
            }
      }
      /* FIXME: needs to adjust status_bits according to the format
       *        and sample rate
       */
      return 0;
}

static snd_pcm_uframes_t
snd_pcm_iec958_write_areas(snd_pcm_t *pcm,
                     const snd_pcm_channel_area_t *areas,
                     snd_pcm_uframes_t offset,
                     snd_pcm_uframes_t size,
                     const snd_pcm_channel_area_t *slave_areas,
                     snd_pcm_uframes_t slave_offset,
                     snd_pcm_uframes_t *slave_sizep)
{
      snd_pcm_iec958_t *iec = pcm->private_data;
      if (size > *slave_sizep)
            size = *slave_sizep;
      iec->func(iec, slave_areas, slave_offset,
              areas, offset, 
              pcm->channels, size);
      *slave_sizep = size;
      return size;
}

static snd_pcm_uframes_t
snd_pcm_iec958_read_areas(snd_pcm_t *pcm,
                    const snd_pcm_channel_area_t *areas,
                    snd_pcm_uframes_t offset,
                    snd_pcm_uframes_t size,
                    const snd_pcm_channel_area_t *slave_areas,
                    snd_pcm_uframes_t slave_offset,
                    snd_pcm_uframes_t *slave_sizep)
{
      snd_pcm_iec958_t *iec = pcm->private_data;
      if (size > *slave_sizep)
            size = *slave_sizep;
      iec->func(iec, areas, offset, 
              slave_areas, slave_offset,
              pcm->channels, size);
      *slave_sizep = size;
      return size;
}

static int snd_pcm_iec958_init(snd_pcm_t *pcm)
{
      snd_pcm_iec958_t *iec = pcm->private_data;
      iec->counter = 0;
      return 0;
}

static void snd_pcm_iec958_dump(snd_pcm_t *pcm, snd_output_t *out)
{
      snd_pcm_iec958_t *iec = pcm->private_data;
      snd_output_printf(out, "IEC958 subframe conversion PCM (%s)\n", 
                    snd_pcm_format_name(iec->sformat));
      if (pcm->setup) {
            snd_output_printf(out, "Its setup is:\n");
            snd_pcm_dump_setup(pcm, out);
      }
      snd_output_printf(out, "Slave: ");
      snd_pcm_dump(iec->plug.gen.slave, out);
}

static snd_pcm_ops_t snd_pcm_iec958_ops = {
      .close = snd_pcm_generic_close,
      .info = snd_pcm_generic_info,
      .hw_refine = snd_pcm_iec958_hw_refine,
      .hw_params = snd_pcm_iec958_hw_params,
      .hw_free = snd_pcm_generic_hw_free,
      .sw_params = snd_pcm_generic_sw_params,
      .channel_info = snd_pcm_generic_channel_info,
      .dump = snd_pcm_iec958_dump,
      .nonblock = snd_pcm_generic_nonblock,
      .async = snd_pcm_generic_async,
      .mmap = snd_pcm_generic_mmap,
      .munmap = snd_pcm_generic_munmap,
};

/**
 * \brief Creates a new IEC958 subframe conversion PCM
 * \param pcmp Returns created PCM handle
 * \param name Name of PCM
 * \param sformat Slave (destination) format
 * \param slave Slave PCM handle
 * \param close_slave When set, the slave PCM handle is closed with copy PCM
 * \param status_bits The IEC958 status bits
 * \param preamble_vals The preamble byte values
 * \retval zero on success otherwise a negative error code
 * \warning Using of this function might be dangerous in the sense
 *          of compatibility reasons. The prototype might be freely
 *          changed in future.
 */           
00446 int snd_pcm_iec958_open(snd_pcm_t **pcmp, const char *name, snd_pcm_format_t sformat,
                  snd_pcm_t *slave, int close_slave,
                  const unsigned char *status_bits,
                  const unsigned char *preamble_vals)
{
      snd_pcm_t *pcm;
      snd_pcm_iec958_t *iec;
      int err;
      static unsigned char default_status_bits[] = {
            IEC958_AES0_CON_EMPHASIS_NONE,
            IEC958_AES1_CON_ORIGINAL | IEC958_AES1_CON_PCM_CODER,
            0,
            IEC958_AES3_CON_FS_48000
      };

      assert(pcmp && slave);
      if (snd_pcm_format_linear(sformat) != 1 &&
          sformat != SND_PCM_FORMAT_IEC958_SUBFRAME_LE &&
          sformat != SND_PCM_FORMAT_IEC958_SUBFRAME_BE)
            return -EINVAL;
      iec = calloc(1, sizeof(snd_pcm_iec958_t));
      if (!iec) {
            return -ENOMEM;
      }
      snd_pcm_plugin_init(&iec->plug);
      iec->sformat = sformat;
      iec->plug.read = snd_pcm_iec958_read_areas;
      iec->plug.write = snd_pcm_iec958_write_areas;
      iec->plug.init = snd_pcm_iec958_init;
      iec->plug.undo_read = snd_pcm_plugin_undo_read_generic;
      iec->plug.undo_write = snd_pcm_plugin_undo_write_generic;
      iec->plug.gen.slave = slave;
      iec->plug.gen.close_slave = close_slave;

      if (status_bits)
            memcpy(iec->status, status_bits, sizeof(iec->status));
      else
            memcpy(iec->status, default_status_bits, sizeof(default_status_bits));

      memcpy(iec->preamble, preamble_vals, 3);

      err = snd_pcm_new(&pcm, SND_PCM_TYPE_IEC958, name, slave->stream, slave->mode);
      if (err < 0) {
            free(iec);
            return err;
      }
      pcm->ops = &snd_pcm_iec958_ops;
      pcm->fast_ops = &snd_pcm_plugin_fast_ops;
      pcm->private_data = iec;
      pcm->poll_fd = slave->poll_fd;
      pcm->poll_events = slave->poll_events;
      snd_pcm_set_hw_ptr(pcm, &iec->plug.hw_ptr, -1, 0);
      snd_pcm_set_appl_ptr(pcm, &iec->plug.appl_ptr, -1, 0);
      *pcmp = pcm;

      return 0;
}

/*! \page pcm_plugins

\section pcm_plugins_iec958 Plugin: IEC958

This plugin converts 32bit IEC958 subframe samples to linear, or linear to
32bit IEC958 subframe samples.

\code
pcm.name {
        type iec958             # IEC958 subframe conversion PCM
        slave STR               # Slave name
        # or
        slave {                 # Slave definition
                pcm STR         # Slave PCM name
                # or
                pcm { }         # Slave PCM definition
        }
      [status status-bytes]   # IEC958 status bits (given in byte array)
      # IEC958 preamble bits definitions
      # B/M/W or Z/X/Y, B = block start, M = even subframe, W = odd subframe
      # As default, Z = 0x08, Y = 0x04, X = 0x02
      [preamble.z or preamble.b val]
      [preamble.x or preamble.m val]
      [preamble.y or preamble.w val]
}
\endcode

\subsection pcm_plugins_iec958_funcref Function reference

<UL>
  <LI>snd_pcm_iec958_open()
  <LI>_snd_pcm_iec958_open()
</UL>

*/

/**
 * \brief Creates a new IEC958 subframe conversion PCM
 * \param pcmp Returns created PCM handle
 * \param name Name of PCM
 * \param root Root configuration node
 * \param conf Configuration node with copy PCM description
 * \param stream Stream type
 * \param mode Stream mode
 * \retval zero on success otherwise a negative error code
 * \warning Using of this function might be dangerous in the sense
 *          of compatibility reasons. The prototype might be freely
 *          changed in future.
 */
00553 int _snd_pcm_iec958_open(snd_pcm_t **pcmp, const char *name,
                   snd_config_t *root, snd_config_t *conf, 
                   snd_pcm_stream_t stream, int mode)
{
      snd_config_iterator_t i, next;
      int err;
      snd_pcm_t *spcm;
      snd_config_t *slave = NULL, *sconf;
      snd_config_t *status = NULL, *preamble = NULL;
      snd_pcm_format_t sformat;
      unsigned char status_bits[24];
      unsigned char preamble_vals[3] = {
            0x08, 0x02, 0x04 /* Z, X, Y */
      };

      snd_config_for_each(i, next, conf) {
            snd_config_t *n = snd_config_iterator_entry(i);
            const char *id;
            if (snd_config_get_id(n, &id) < 0)
                  continue;
            if (snd_pcm_conf_generic_id(id))
                  continue;
            if (strcmp(id, "slave") == 0) {
                  slave = n;
                  continue;
            }
            if (strcmp(id, "status") == 0) {
                  if (snd_config_get_type(n) != SND_CONFIG_TYPE_COMPOUND) {
                        SNDERR("Invalid type for %s", id);
                        return -EINVAL;
                  }
                  status = n;
                  continue;
            }
            if (strcmp(id, "preamble") == 0) {
                  if (snd_config_get_type(n) != SND_CONFIG_TYPE_COMPOUND) {
                        SNDERR("Invalid type for %s", id);
                        return -EINVAL;
                  }
                  preamble = n;
                  continue;
            }
            SNDERR("Unknown field %s", id);
            return -EINVAL;
      }
      memset(status_bits, 0, sizeof(status_bits));
      if (status) {
            snd_config_iterator_t i, inext;
            int bytes = 0;
            snd_config_for_each(i, inext, status) {
                  long val;
                  snd_config_t *n = snd_config_iterator_entry(i);
                  if (snd_config_get_type(n) != SND_CONFIG_TYPE_INTEGER) {
                        SNDERR("invalid IEC958 status bits");
                        return -EINVAL;
                  }
                  err = snd_config_get_integer(n, &val);
                  if (err < 0) {
                        SNDERR("invalid IEC958 status bits");
                        return err;
                  }
                  status_bits[bytes] = val;
                  bytes++;
                  if (bytes >= (int)sizeof(status_bits))
                        break;
            }
            // fprintf(stderr, "STATUS bits: %02x %02x %02x %02x\n", status_bits[0], status_bits[1], status_bits[2], status_bits[3]);
      }
      if (preamble) {
            snd_config_iterator_t i, inext;
            snd_config_for_each(i, inext, status) {
                  long val;
                  snd_config_t *n = snd_config_iterator_entry(i);
                  const char *id;
                  int idx;
                  if (snd_config_get_id(n, &id) < 0)
                        continue;
                  if (strcmp(id, "b") == 0 || strcmp(id, "z") == 0)
                        idx = PREAMBLE_Z;
                  else if (strcmp(id, "m") == 0 || strcmp(id, "x") == 0)
                        idx = PREAMBLE_X;
                  else if (strcmp(id, "w") == 0 || strcmp(id, "y") == 0)
                        idx = PREAMBLE_Y;
                  else {
                        SNDERR("invalid IEC958 preamble type %s", id);
                        return -EINVAL;
                  }
                  err = snd_config_get_integer(n, &val);
                  if (err < 0) {
                        SNDERR("invalid IEC958 preamble value");
                        return err;
                  }
                  preamble_vals[idx] = val;
            }
      }
      if (!slave) {
            SNDERR("slave is not defined");
            return -EINVAL;
      }
      err = snd_pcm_slave_conf(root, slave, &sconf, 1,
                         SND_PCM_HW_PARAM_FORMAT, SCONF_MANDATORY, &sformat);
      if (err < 0)
            return err;
      if (snd_pcm_format_linear(sformat) != 1 &&
          sformat != SND_PCM_FORMAT_IEC958_SUBFRAME_LE &&
          sformat != SND_PCM_FORMAT_IEC958_SUBFRAME_BE) {
            snd_config_delete(sconf);
            SNDERR("invalid slave format");
            return -EINVAL;
      }
      err = snd_pcm_open_slave(&spcm, root, sconf, stream, mode);
      snd_config_delete(sconf);
      if (err < 0)
            return err;
      err = snd_pcm_iec958_open(pcmp, name, sformat, spcm, 1,
                          status ? status_bits : NULL,
                          preamble_vals);
      if (err < 0)
            snd_pcm_close(spcm);
      return err;
}
#ifndef DOC_HIDDEN
SND_DLSYM_BUILD_VERSION(_snd_pcm_iec958_open, SND_PCM_DLSYM_VERSION);
#endif

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