Hi,
I have a blue-tooth headset connected to Ubuntu 8.04. I've created
~/.asoundrc as below:
pcm.bluetooth {
type bluetooth
device 20:04:07:80:BC:89
profile voice
}
ctl.bluetooth {
type bluetooth
}
now I can use command `aplay -Dbluetooth -v 2.wav` to play sound to the
headset, but the sound is little bit wired.
Playing WAVE '2.wav' : Signed 16 bit Little Endian, Rate 16000 Hz, Mono
Warning: rate is not accurate (requested = 16000Hz, got = 8000Hz)
please, try the plug plugin (-Dplug:bluetooth)
Bluetooth Audio Device
Its setup is:
stream : PLAYBACK
access : RW_INTERLEAVED
format : S16_LE
subformat : STD
channels : 1
rate : 8000
exact rate : 8000 (8000/1)
msbits : 16
buffer_size : 4000
period_size : 1000
period_time : 125000
tstamp_mode : NONE
period_step : 1
avail_min : 1000
period_event : 0
start_threshold : 4000
stop_threshold : 4000
silence_threshold: 0
silence_size : 0
boundary : 2097152000
So I input command according to the aplay's recommendation `aplay
-Dplug:bluetooth -v 2.wav`. The problem comes out.
aplay -Dplug:bluetooth -v 2.wav
Playing WAVE '2.wav' : Signed 16 bit Little Endian, Rate 16000 Hz, Mono
Plug PCM: Rate conversion PCM (8000, sformat=S16_LE)
Its setup is:
stream : PLAYBACK
access : RW_INTERLEAVED
format : S16_LE
subformat : STD
channels : 1
rate : 16000
exact rate : 16000 (16000/1)
msbits : 16
buffer_size : 8000
period_size : 2000
period_time : 125000
tstamp_mode : NONE
period_step : 1
avail_min : 2000
period_event : 0
start_threshold : 8000
stop_threshold : 8000
silence_threshold: 0
silence_size : 0
boundary : 2097152000
Slave: Bluetooth Audio Device
Its setup is:
stream : PLAYBACK
access : MMAP_INTERLEAVED
format : S16_LE
subformat : STD
channels : 1
rate : 8000
exact rate : 8000 (8000/1)
msbits : 16
buffer_size : 4000
period_size : 1000
period_time : 125000
tstamp_mode : NONE
period_step : 1
avail_min : 1000
period_event : 0
start_threshold : 4000
stop_threshold : 4000
silence_threshold: 0
silence_size : 0
boundary : 2097152000
It seems that ALSA plugs rate plugin. But I hear NOTHING from my headset
and aplay seems suspended. I turn on bluez debug flag and rebuild it. I
find the bluez suspending at 'bluetooth_playback_poll_descriptors'.
Sep 7 23:18:59 alex-laptop aplay: DEBUG: pcm_bluetooth.c 930
bluetooth_hsp_write: count=0 frames_to_read=24
Sep 7 23:18:59 alex-laptop aplay: DEBUG: pcm_bluetooth.c 993
bluetooth_hsp_write: returning 24
Sep 7 23:18:59 alex-laptop aplay: DEBUG: pcm_bluetooth.c 912
bluetooth_hsp_write: areas->step=16 areas->first=0 offset=0, size=1000
io->nonblock=0 io->hw_ptr=0 io->appl_ptr=0 stream.fd=8 link_mtu=48
data->count=0
Sep 7 23:18:59 alex-laptop aplay: DEBUG: pcm_bluetooth.c 930
bluetooth_hsp_write: count=0 frames_to_read=24
Sep 7 23:18:59 alex-laptop aplay: DEBUG: pcm_bluetooth.c 993
bluetooth_hsp_write: returning 24
Sep 7 23:18:59 alex-laptop aplay: DEBUG: pcm_bluetooth.c 802
bluetooth_playback_poll_descriptors: Space =2 pfd[0].fd=5 pfd[1].fd=6
Sep 7 23:19:01 alex-laptop audio[7979]: Received AT+VGS=11
Now I go deep into ALSA then I find ALSA suspending at:
int snd_pcm_wait_nocheck(snd_pcm_t *pcm, int timeout)
{
struct pollfd *pfd;
unsigned short *revents;
int i, npfds, pollio, err, err_poll;
npfds = snd_pcm_poll_descriptors_count(pcm);
if (npfds <= 0 || npfds >= 16) {
SNDERR("Invalid poll_fds %d\n", npfds);
return -EIO;
}
pfd = alloca(sizeof(*pfd) * npfds);
revents = alloca(sizeof(*revents) * npfds);
syslog( LOG_INFO, "%s", __FUNCTION__ );
err = snd_pcm_poll_descriptors(pcm, pfd, npfds);
if (err < 0)
return err;
if (err != npfds) {
SNDMSG("invalid poll descriptors %d\n", err);
return -EIO;
}
do {
pollio = 0;
err_poll = poll(pfd, npfds, timeout); <-------------
It seems the bluez doesn't feed ALSA some signals. But why? I notice
'bluetooth_playback_start' haven't been invoked. Is it the point? Then I
keep tracing ALSA. I find in snd_pcm_rate_commit_area
result = snd_pcm_mmap_commit(rate->gen.slave, slave_offset,
slave_size);
if (result < (snd_pcm_sframes_t)slave_size) {
if (result < 0)
return result;
result = snd_pcm_rewind(rate->gen.slave, result); <-----------
if (result < 0)
return result;
return 0;
}
The snd_pcm_mmap_commit returns with 24 which indicates bluetooth SCO
link mtu(48bytes). And it causes snd_pcm_rewind being called after every
package sent by bluetooth SCO link. Look at this piece of code in
snd_pcm_write_areas:
if (state == SND_PCM_STATE_PREPARED) {
snd_pcm_sframes_t hw_avail = pcm->buffer_size - avail;
hw_avail += frames;
/* some plugins might automatically start the stream */
state = snd_pcm_state(pcm);
if (state == SND_PCM_STATE_PREPARED &&
hw_avail >= (snd_pcm_sframes_t) pcm->start_threshold) {
err = snd_pcm_start(pcm);
if (err < 0)
goto _end;
}
}
the 'avail' will be equal to pcm->buffer due to snd_pcm_rewind,
therefore the condition hw_avail>=pcm->start_threshold will not be
satisfied forever. That's why snd_pcm_start can't be called.
I don't know the mechanism of ALSA and I just assume ALSA wanna bluez
plugin sending whole period_size instead of only one 48bytes package. I
revise the bluez plugin:
#if 0 // this section is original bluez
frame_size = areas->step / 8;
if ((data->count + size * frame_size) <= data->link_mtu)
frames_to_read = size;
else
frames_to_read = (data->link_mtu - data->count) / frame_size;
DBG("count=%d frames_to_read=%lu", data->count, frames_to_read);
/* Ready for more data */
buff = (uint8_t *) areas->addr +
(areas->first + areas->step * offset) / 8;
memcpy(data->buffer + data->count, buff, frame_size * frames_to_read);
/* Remember we have some frames in the pipe now */
data->count += frames_to_read * frame_size;
if (data->count != data->link_mtu) {
ret = frames_to_read;
goto done;
}
rsend = send(data->stream.fd, data->buffer, data->link_mtu,
io->nonblock ? MSG_DONTWAIT : 0);
if (rsend > 0) {
/* Reset count pointer */
data->count = 0;
ret = frames_to_read;
} else if (rsend < 0)
ret = (errno == EPIPE) ? -EIO : -errno;
else
ret = -EIO;
#else
frame_size = areas->step / 8;
buff = (uint8_t *) areas->addr +
(areas->first + areas->step * offset) / 8;
tobesent = frame_size*size;
while( rsend<tobesent )
{
if( tobesent-rsend>data->link_mtu )
sent = send(data->stream.fd, buff+counter*data->link_mtu,
data->link_mtu,
io->nonblock ? MSG_DONTWAIT : 0);
else
sent = send(data->stream.fd, buff+counter*data->link_mtu,
tobesent-rsend,
io->nonblock ? MSG_DONTWAIT : 0);
if( sent > 0 )
{
if( sent != data->link_mtu && tobesent-rsend > data->link_mtu )
DBG("got problem!");
counter++;
rsend+=sent;
}
else if (rsend < 0)
{
ret = (errno == EPIPE) ? -EIO : -errno;
break;
}
else
{
ret = -EIO;
break;
}
}
ret = size;
#endif
After this revision, the headset works but the performance isn't as good
as playing MONO 8000Hz wav directly to headset with 'aplay -Dbluetooth
1.wav'. Any hints would be appreciated.
Regards,
Galaha
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