zynq音楽再生プロセス

『zynq audio pcm DMA』でsnd_に言及pcm_writei()という関数はalsa libのインタフェースであり、以下のように実現されています.

snd_pcm_sframes_t snd_pcm_writei(snd_pcm_t *pcm, const void *buffer, snd_pcm_uframes_t size)
{
	assert(pcm);
	assert(size == 0 || buffer);
	if (CHECK_SANITY(! pcm->setup)) {
		SNDMSG("PCM not set up");
		return -EIO;
	}
	if (pcm->access != SND_PCM_ACCESS_RW_INTERLEAVED) {
		SNDMSG("invalid access type %s", snd_pcm_access_name(pcm->access));
		return -EINVAL;
	}
	return _snd_pcm_writei(pcm, buffer, size);
}

この関数が呼び出されました_snd_pcm_writeiは具体的な任務を実現する.

static inline snd_pcm_sframes_t _snd_pcm_writei(snd_pcm_t *pcm, const void *buffer, snd_pcm_uframes_t size)
{
	return pcm->fast_ops->writei(pcm->fast_op_arg, buffer, size);
}

そして_snd_pcm_writeiは実際に関数ポインタ操作セットを呼び出して書き込み操作を実現した.このwritei関数は実際にalsaライブラリのsnd_ですpcm_hw_writei().

static snd_pcm_sframes_t snd_pcm_hw_writei(snd_pcm_t *pcm, const void *buffer, snd_pcm_uframes_t size)
{
	int err;
	snd_pcm_hw_t *hw = pcm->private_data;
	int fd = hw->fd;
	struct snd_xferi xferi;
	xferi.buf = (char*) buffer;
	xferi.frames = size;
	xferi.result = 0; /* make valgrind happy */
	err = ioctl(fd, SNDRV_PCM_IOCTL_WRITEI_FRAMES, &xferi);
	err = err >= 0 ? sync_ptr(hw, SNDRV_PCM_SYNC_PTR_APPL) : -errno;
#ifdef DEBUG_RW
	fprintf(stderr, "hw_writei: frames = %li, xferi.result = %li, err = %i
", size, xferi.result, err);
#endif
	if (err < 0)
		return snd_pcm_check_error(pcm, err);
	return xferi.result;
}

この関数は実際にioctl関数を呼び出して関連する操作を完了し、実際にalsa libはpcm操作のパッケージであり、alsaのユーザ空間プログラミングを簡略化した.
ioctlシステム呼び出しはlinuxカーネルヘッダファイルsyscallsである.hで宣言した.

<4>[] (snd_pcm_playback_ioctl1) from [] (do_vfs_ioctl+0x564/0x688)
<4>[] (do_vfs_ioctl) from [] (SyS_ioctl+0x34/0x5c)
<4>[] (SyS_ioctl) from [] (ret_fast_syscall+0x0/0x3c)

なぜlinux kernel対応にsnd_pcm_writei?これは登録時に確定します.

snd_soc_register_card-->snd_card_register--->snd_device_register_all-->__snd_device_register.part.0-->
snd_pcm_dev_register--->snd_pcm_dev_register()
{
		err = snd_register_device(devtype, pcm->card, pcm->device,
					  &snd_pcm_f_ops[cidx], pcm,
					  &pcm->streams[cidx].dev);
}
.unlocked_ioctl =	snd_pcm_playback_ioctl,
snd_pcm_playback_ioctl--->snd_pcm_playback_ioctl1

ユーザ空間伝達のioctlコマンドはSNDRV_であるためPCM_IOCTL_WRITEI_FRAMESでは、対応するcase文が実行されます.プレイコールの流れは次のとおりです.
snd_pcm_playback_ioctl1-->snd_pcm_common_ioctl1-->snd_pcm_action_lock_irq-->snd_pcm_action-->snd_pcm_action_single-->snd_pcm_do_start-->soc_pcm_trigger

2807 static int snd_pcm_playback_ioctl1(struct file *file,
2808                    struct snd_pcm_substream *substream,
2809                    unsigned int cmd, void __user *arg)
2810 {
2811     if (snd_BUG_ON(!substream))
2812         return -ENXIO;
2813     if (snd_BUG_ON(substream->stream != SNDRV_PCM_STREAM_PLAYBACK))
2814         return -EINVAL;
2815 
2816     switch (cmd) {
2817     case SNDRV_PCM_IOCTL_WRITEI_FRAMES:
2818     {
2819         struct snd_xferi xferi;
2820         struct snd_xferi __user *_xferi = arg;
2821         struct snd_pcm_runtime *runtime = substream->runtime;
2822         snd_pcm_sframes_t result;
2823         if (runtime->status->state == SNDRV_PCM_STATE_OPEN)
2824             return -EBADFD;
2825         if (put_user(0, &_xferi->result))
2826             return -EFAULT;
2827         if (copy_from_user(&xferi, _xferi, sizeof(xferi)))
2828             return -EFAULT;
2829         result = snd_pcm_lib_write(substream, xferi.buf, xferi.frames);
2830         __put_user(result, &_xferi->result);
2831         return result < 0 ? result : 0;
2832     }

この関数呼び出しのwrite、最終呼び出し
インプリメンテーション

static int soc_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
{
    struct snd_soc_pcm_runtime *rtd = substream->private_data;
    struct snd_soc_platform *platform = rtd->platform;
    struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
    struct snd_soc_dai *codec_dai;
    int i, ret;

    for (i = 0; i < rtd->num_codecs; i++) {
        codec_dai = rtd->codec_dais[i];
        if (codec_dai->driver->ops && codec_dai->driver->ops->trigger) {
            ret = codec_dai->driver->ops->trigger(substream,
                                  cmd, codec_dai);
            if (ret < 0)
                return ret;
        }
    }

    if (platform->driver->ops && platform->driver->ops->trigger) {
        ret = platform->driver->ops->trigger(substream, cmd);
        if (ret < 0)
            return ret;
    }

    if (cpu_dai->driver->ops && cpu_dai->driver->ops->trigger) {
        ret = cpu_dai->driver->ops->trigger(substream, cmd, cpu_dai);
        if (ret < 0)
            return ret;
    }

    if (rtd->dai_link->ops && rtd->dai_link->ops->trigger) {
        ret = rtd->dai_link->ops->trigger(substream, cmd);
        if (ret < 0)
            return ret;
    }

    return 0;
}

ここでは4つのtriger関数が呼び出され、各関数は1つのtriggerに対応する.platformに対応するtrigger関数はsnd_dmaengine_pcm_trigger()、cpu側のtrigger関数はaxi_i2s_trigger().codecはtrigger関数を実現していない.axi-i2s_trigger()は、cpu側daiのイネーブルを設定するために使用されます.本当にDMAに関連する操作は

184 int snd_dmaengine_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
185 {
186     struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
187     struct snd_pcm_runtime *runtime = substream->runtime;
188     int ret;
189 
190     switch (cmd) {
191     case SNDRV_PCM_TRIGGER_START:
192         ret = dmaengine_pcm_prepare_and_submit(substream);
193         if (ret)
194             return ret;
195         dma_async_issue_pending(prtd->dma_chan);
196         break;
197     case SNDRV_PCM_TRIGGER_RESUME:
198     case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
199         dmaengine_resume(prtd->dma_chan);
200         break;
201     case SNDRV_PCM_TRIGGER_SUSPEND:
202         if (runtime->info & SNDRV_PCM_INFO_PAUSE)
203             dmaengine_pause(prtd->dma_chan);
204         else
205             dmaengine_terminate_all(prtd->dma_chan);
206         break;
207     case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
208         dmaengine_pause(prtd->dma_chan);
209         break;
210     case SNDRV_PCM_TRIGGER_STOP:
211         dmaengine_terminate_all(prtd->dma_chan);
212         break;
213     default:
214         return -EINVAL;
215     }
216 
217     return 0;
218 }
219 EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_trigger);

この関数はdmaengineを呼び出します.pcm_prepare_and_submit()は送信操作を行う.

145 static int dmaengine_pcm_prepare_and_submit(struct snd_pcm_substream *substream)
146 {
147     struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
148     struct dma_chan *chan = prtd->dma_chan;
149     struct dma_async_tx_descriptor *desc;
150     enum dma_transfer_direction direction;
151     unsigned long flags = DMA_CTRL_ACK;
152 
153     direction = snd_pcm_substream_to_dma_direction(substream);
154 
155     if (!substream->runtime->no_period_wakeup)
156         flags |= DMA_PREP_INTERRUPT;
157 
158     prtd->pos = 0;
159     desc = dmaengine_prep_dma_cyclic(chan,
160         substream->runtime->dma_addr,
161         snd_pcm_lib_buffer_bytes(substream),
162         snd_pcm_lib_period_bytes(substream), direction, flags);
163 
164     if (!desc)
165         return -ENOMEM;
166 
167     desc->callback = dmaengine_pcm_dma_complete;
168     desc->callback_param = substream;
169     prtd->cookie = dmaengine_submit(desc);
170 
171     return 0;
172 }

上のこの関数159はpl 330を呼び出します.prep_dma_cyclic()関数、dmaengine_submit()呼び出しpl 330_tx_submit()関数は送信記述子を追加します.