pcm_write

tinyalsa 的 pcm_write:

static int pcm_write_wrapper(struct pcm *pcm, const void * buffer, size_t bytes, int flags)
{
    int ret = 0;
    if(flags & PCM_MMAP)
         ret = pcm_mmap_write(pcm, (void *)buffer, bytes);
    else
         ret = pcm_write(pcm, (void *)buffer, bytes);

一般都沒有用 MMAP.
所以都是直接 call pcm_write( )

tinyalsa 實做的 pcm_write( ) 就是用for loop 把 buffer 一一寫入 ioctl:

    struct snd_xferi x;

    x.buf = (void*)data;
    x.frames = count / (pcm->config.channels *
                        pcm_format_to_bits(pcm->config.format) / 8);

    ioctl(pcm->fd, SNDRV_PCM_IOCTL_WRITEI_FRAMES, &x))

這樣就進入 kernel 了..

kernel 的 snd_pcm_playback_ioctl1 呼叫 snd_pcm_lib_write 來做：

static int snd_pcm_lib_write_transfer(struct snd_pcm_substream *substream,
                                      unsigned int hwoff,
                                      unsigned long data, unsigned int off,
                                      snd_pcm_uframes_t frames)
{
        struct snd_pcm_runtime *runtime = substream->runtime;
        int err;
        char __user *buf = (char __user *) data + frames_to_bytes(runtime, off);

        if (substream->ops->copy) {
                if ((err = substream->ops->copy(substream, -1, hwoff, buf, frames)) < 0)
                        return err;
        } else {
                char *hwbuf = runtime->dma_area + frames_to_bytes(runtime, hwoff);
                if (copy_from_user(hwbuf, buf, frames_to_bytes(runtime, frames)))
                        return -EFAULT;
        }
        return 0;
}

---

錯了。結果是用 MMAP...
所以，trace 到最後，是 call kernel 的 snd_pcm_sync_ptr..

修改一下 hardware/imx/alsa/tinyalsa_hal.c, 拿掉 MMAP, 就會 call pcm_write(), 就可以換掉 pcm_write 了..

	diff --git a/alsa/tinyalsa_hal.c b/alsa/tinyalsa_hal.c
	index a4644ac..2b85b88 100644
	--- a/alsa/tinyalsa_hal.c
	+++ b/alsa/tinyalsa_hal.c
	@@ -16,7 +16,7 @@
	/* Copyright (C) 2012-2015 Freescale Semiconductor, Inc. */
	#define LOG_TAG "audio_hw_primary"
	-//#define LOG_NDEBUG 0
	+#define LOG_NDEBUG 0
	#include <errno.h>
	#include <pthread.h>
	@@ -524,7 +524,7 @@ static int start_output_stream_primary(struct imx_stream_out *out)
	pcm_device = out->device & (AUDIO_DEVICE_OUT_ALL & ~AUDIO_DEVICE_OUT_AUX_DIGITAL);
	if (pcm_device && (adev->active_output[OUTPUT_ESAI] == NULL || adev->active_output[OUTPUT_ESAI]->standby)) {
	- out->write_flags[PCM_NORMAL] = PCM_OUT | PCM_MMAP | PCM_MONOTONIC;
	+ out->write_flags[PCM_NORMAL] = PCM_OUT | PCM_MONOTONIC;
	out->write_threshold[PCM_NORMAL] = PLAYBACK_LONG_PERIOD_COUNT * LONG_PERIOD_SIZE;
	out->config[PCM_NORMAL] = pcm_config_mm_out;
	@@ -1175,6 +1175,27 @@ static int pcm_read_wrapper(struct pcm *pcm, const void * buffer, size_t bytes)
	return ret;
	}
	+static int s_pcm_write(struct pcm *pcm, void * buffer, size_t bytes)
	+{
	+ int i;
	+ unsigned short *dst;
	+ unsigned short *src;
	+ unsigned short patten = 0x0000;
	+ int rc;
	+
	+ dst = (unsigned short*)malloc(bytes);
	+ src = (unsigned short*)buffer;
	+
	+ for(i=0 ; i<bytes/2 ; i++)
	+ dst[i]=src[i];
	+
	+ rc = pcm_write(pcm, (void*)dst, bytes);
	+ free(dst);
	+ return rc;
	+
	+
	+}
	static int pcm_write_wrapper(struct pcm *pcm, const void * buffer, size_t bytes, int flags)
	{
	@@ -1182,7 +1203,7 @@ static int pcm_write_wrapper(struct pcm *pcm, const void * buffer, size_t bytes,
	if(flags & PCM_MMAP)
	ret = pcm_mmap_write(pcm, (void *)buffer, bytes);
	else
	- ret = pcm_write(pcm, (void *)buffer, bytes);
	+ ret = s_pcm_write(pcm, (void *)buffer, bytes);
	if(ret !=0) {
	ALOGW("ret %d, pcm write %d error %s", ret, bytes, pcm_get_error(pcm));
	@@ -1200,7 +1221,7 @@ static int pcm_write_wrapper(struct pcm *pcm, const void * buffer, size_t bytes,
	if(flags & PCM_MMAP)
	ret = pcm_mmap_write(pcm, (void *)buffer, bytes);
	else
	- ret = pcm_write(pcm, (void *)buffer, bytes);
	+ ret = s_pcm_write(pcm, (void *)buffer, bytes);
	}
	return ret;

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