I would like to discuss possible changes in the sco to hci-usb layer
api. I would like people to agree the changes before I go ahead and code
them. I don't have exact function names etc. yet, but just a general
idea of what one needs to do in order to implement an alsa interface to
bluez.
There are a number of problems with the current usb-hci.c driver.
I have a dirty fix for sound recording, but playback will need a lot of
work.
If you want recording to work, just put in a for loop round the
"static int hci_usb_isoc_rx_submit(struct hci_usb *husb)" function to
make it execute twice. See "e.g." below.
It is a very dirty fix, because I don't think that everything gets freed
when not in use, but at least it records sound at the correct speed.
The playback problem is a scheduling problem.
The "hci_usb_tx_complete" function uses the scheduler to kick off the
next transmission, but the scheduler is too slow, and the correct method
to use is getting the "hci_usb_tx_complete" function to retrieve the
next packet to send from a ring buffer, and send it immeadiately during
the "hci_usb_tx_complete" function. This is how the current usbaudio.c
does it, so it proves that this method will work.
So, I will need to implement a ring buffer.
At the same time I want to implement sound output via alsa, so I want to
make sure we have a good api to achieve that.
alsa requires certain information from the sound card (ring buffer
position etc.), and I will have to make sure that the information alsa
needs in available, by maybe adding new api calls through the sco layer
to the usb-hci.c layer. I think it would be a good idea to completely
separate the isoc(sound) urb path from the int/bulk/control urb path.
We also have the added complication that the alsa ring buffer is
composed of just sound samples, but the sco layer converts that to
packets with a header so the hci-usb.c layer has to deal with packets
instead of samples.
For 8 bit mono sound, SCO creates packets with 3 header bytes, and 24
sound samples. hci-usb.c then has to take each 27 byte packet and cut it
down into 3 slices each 9 bytes in length. All packet sizes and slice
sizes vary depending on 8/16 bits samples, and mono/stereo etc.
So, there is going to be quite a lot of manipulation of the sound
samples as they pass from alsa to the bluetooth device.
The questions I am still trying to decide are: -
1) When should the conversion from alsa ring buffer to packets take
place. So far the only workable solution I have come up with is that the
"hci_usb_tx_complete" makes a callback all the way to the sco layer, and
the sco layer grabs 24 bytes form the alsa ring buffer, adds it's header
and returns from the callback.
2) interface to alsa. I think this should happen just above the SCO
layer, but also ensuring that the SCO layer has enought api links with
the hci-usb.c layer to be able to service all the alsa-driver api
requirements.
3) Once that all works, modify the other low level hardware drivers to
work with it. e.g. bluecard_cs.c etc.
The final result will be: -
1) a small tool that will link a particular paired bluetooth device to a
particular PCM device for alsa to work with. This tool will basically
just take destination BTADDR and channel number to use, because alsa
will have no knowledge of that sort of info. It will add a new sound
card instance for each bluetooth device.
2) alsa will just think that the bluetooth headset is a normal soundcard.
3) This would make integration with current audio applications simple,
because alsa supports the alsa-api as well as emulate the oss-api, so
current audio applications would need no changes.
4) We could even implement headset "in the vicinity" detection, so that
when the headset transitioned from out of range to in range, your
computer could say hello!
Cheers
James
e.g.
static int hci_usb_isoc_rx_submit(struct hci_usb *husb)
{
struct _urb *_urb;
struct urb *urb;
int err, mtu, size;
void *buf;
int n;
for(n=0;n<2;n++) {
mtu = husb->isoc_in_ep->wMaxPacketSize;
BT_INFO("isoc_rx_submit: mtu=%d", mtu);
size = mtu * HCI_MAX_ISOC_FRAMES;
buf = kmalloc(size, GFP_ATOMIC);
if (!buf)
return -ENOMEM;
_urb = _urb_alloc(HCI_MAX_ISOC_FRAMES, GFP_ATOMIC);
if (!_urb) {
kfree(buf);
return -ENOMEM;
}
_urb->type = HCI_SCODATA_PKT;
_urb_queue_tail(__pending_q(husb, _urb->type), _urb);
urb = &_urb->urb;
urb->context = husb;
urb->dev = husb->udev;
urb->pipe = usb_rcvisocpipe(husb->udev,
husb->isoc_in_ep->bEndpointAddress);
urb->complete = hci_usb_rx_sync_complete;
urb->transfer_buffer_length = size;
urb->transfer_buffer = buf;
urb->transfer_flags = USB_ISO_ASAP;
__fill_isoc_desc(urb, size, mtu);
BT_DBG("%s urb %p", husb->hdev.name, urb);
err = usb_submit_urb(urb);
if (err) {
BT_ERR("%s isoc rx submit failed urb %p err %d",
husb->hdev.name, urb, err);
_urb_unlink(_urb);
_urb_free(_urb);
kfree(buf);
}
} /* End for loop */
return err;
}
#endif
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At 06:58 AM 7/18/2003, James Courtier-Dutton wrote:
>>The integration of audio is not part of the Bluetooth drivers, because
>>every Bluetooth HCI driver is only a transport driver which have to
>>transport the HCI command, event, ACL and SCO data between the hardware
>>and the HCI core layer. The SCO data would send from the HCI core
>>through the hdev->send() callback and the driver can send the SCO data
>>it gets from the hardware back with hci_recv_frame(). This means that
>>all needed modifications for ALSA and OSS integration have to done in
>>the HCI core or the SCO layer. And all other HCI drivers will still work
>>with SCO like they do now.
>The recv_frame() parts seem to work ok at the moment. (with some modifications as outlined in a previous email)
>The main problem is the send_frame() parts. hdev->send() is the wrong thing to do for ISOC connections (one runs into scheduling problems, buffer underruns and no flow control.).
I'm still not sure what scheduler problems you're talking about.
Current send process looks like this:
app -> sco socket layer -> hci core -> (soft irq) -> hci tx tasklet -> hci driver -> HW
I guess by scheduler you mean scheduling tasklet. But tasklet is extremely fast (we can elevate
tasklet priority if needed) it doesn't go via normal process scheduler, it's softirq within the
kernel itself no context switching, etc.
>A callback method from the hardware is much beter. (e.g. Give me X number of samples NOW!). This is why I suggest a ring buffer and tx/rx complete callbacks from HCI to SCO layer to update ring buffer pointers, and then the alsa or oss layer above that.
>I will do alsa first because there is much less work involved.
>I know the callback/ringbuffer approach works well over usb, because alsa has a usb-audio driver, and it works fine.
The problem is that with PCMCIA, UART, etc based devices you don't know when transfer completes.
ie In USB you submit URB, it completes, you get a callback, in PCMCIA you're not going to get any
completion callbacks.
Also one Bluetooth device can have up to 3 SCO connections information about connection handles and
stuff is maintained by the HCI core. Which means HCI driver has to talk to the core anyway.
Max
At 06:04 AM 7/18/2003, Marcel Holtmann wrote:
>> So, there is going to be quite a lot of manipulation of the sound
>> samples as they pass from alsa to the bluetooth device.
>> The questions I am still trying to decide are: -
>> 1) When should the conversion from alsa ring buffer to packets take
>> place. So far the only workable solution I have come up with is that the
>> "hci_usb_tx_complete" makes a callback all the way to the sco layer, and
>> the sco layer grabs 24 bytes form the alsa ring buffer, adds it's header
>> and returns from the callback.
>> 2) interface to alsa. I think this should happen just above the SCO
>> layer, but also ensuring that the SCO layer has enought api links with
>> the hci-usb.c layer to be able to service all the alsa-driver api
>> requirements.
>> 3) Once that all works, modify the other low level hardware drivers to
>> work with it. e.g. bluecard_cs.c etc.
>
>The native integration of Bluetooth audio within Linux is one of the
>most wanted things. But we can't use ALSA for the 2.4 kernel, because it
>is not a part of the kernel. For the 2.6 this is no problem, but I also
>want to have support for OSS, because there will some people (like me)
>which still uses OSS.
Those people will have to upgrade :). New stuff like this audio support
should be developed in 2.6.
>The integration of audio is not part of the Bluetooth drivers, because
>every Bluetooth HCI driver is only a transport driver which have to
>transport the HCI command, event, ACL and SCO data between the hardware
>and the HCI core layer. The SCO data would send from the HCI core
>through the hdev->send() callback and the driver can send the SCO data
>it gets from the hardware back with hci_recv_frame(). This means that
>all needed modifications for ALSA and OSS integration have to done in
>the HCI core or the SCO layer. And all other HCI drivers will still work
>with SCO like they do now.
150% agree.
Max
At 05:15 AM 7/18/2003, James Courtier-Dutton wrote:
>There are a number of problems with the current usb-hci.c driver.
>I have a dirty fix for sound recording, but playback will need a lot of work.
>If you want recording to work, just put in a for loop round the
>"static int hci_usb_isoc_rx_submit(struct hci_usb *husb)" function to make it execute twice. See "e.g." below.
>
>It is a very dirty fix, because I don't think that everything gets freed when not in use, but at least it records sound at the correct speed.
Actually it's not a dirty fix. I thought that ISOC queuing (ie more than one transfer at a time) is not
support by USB HCD driver. If it supported then the fix is good.
>The playback problem is a scheduling problem.
>The "hci_usb_tx_complete" function uses the scheduler to kick off the next transmission, but the scheduler is too slow, and the correct method to use is getting the "hci_usb_tx_complete" function to retrieve the next packet to send from a ring buffer, and send it immeadiately during the "hci_usb_tx_complete" function.
Which scheduler are you're talking about ?
Take a look at hci_usb_tx_proccess() function, which is called immediately after transfer completes,
it does this:
/* Process SCO queue */
q = __transmit_q(husb, HCI_SCODATA_PKT);
if (!atomic_read(__pending_tx(husb, HCI_SCODATA_PKT)) &&
(skb = skb_dequeue(q))) {
if (hci_usb_send_isoc(husb, skb) < 0)
skb_queue_head(q, skb);
}
So basically HCI USB driver has SCO TX queue and the next packet, if available, is retrived directly
from this queue. Scheduler is not involved here. Again it only does one transfer at a time because
I thought (and still think :)) that multiple ISOC transfers are not supported.
>This is how the current usbaudio.c does it, so it proves that this method will work.
>So, I will need to implement a ring buffer.
>At the same time I want to implement sound output via alsa, so I want to make sure we have a good api to achieve that.
>alsa requires certain information from the sound card (ring buffer position etc.), and I will have to make sure that the information alsa needs in available, by maybe adding new api calls through the sco layer to the usb-hci.c layer.
Those calls should be made into HCI core not HCI USB driver. Think about PCI and PCMCIA and other Bluetooth
devices. We have to make audio support generic.
>I think it would be a good idea to completely separate the isoc(sound) urb path from the int/bulk/control urb path.
I completely disagree. Most of the URB processing is very similar. First version of the driver did have
separate bulk and isoc paths, but the code was pretty much the same that's why it's been combined.
>We also have the added complication that the alsa ring buffer is composed of just sound samples, but the sco layer converts that to packets with a header so the hci-usb.c layer has to deal with packets instead of samples.
>For 8 bit mono sound, SCO creates packets with 3 header bytes, and 24 sound samples. hci-usb.c then has to take each 27 byte packet and cut it down into 3 slices each 9 bytes in length. All packet sizes and slice sizes vary depending on 8/16 bits samples, and mono/stereo etc.
>
>So, there is going to be quite a lot of manipulation of the sound samples as they pass from alsa to the bluetooth device.
>The questions I am still trying to decide are: -
>1) When should the conversion from alsa ring buffer to packets take place. So far the only workable solution I have come up with is that the
>"hci_usb_tx_complete" makes a callback all the way to the sco layer, and the sco layer grabs 24 bytes form the alsa ring buffer, adds it's header and returns from the callback.
Why can't we just pass those samples to the HCI USB driver as soon as they become available ?
Driver will put queue them into tx queue and use that queue when transfer completes.
>2) interface to alsa. I think this should happen just above the SCO layer, but also ensuring that the SCO layer
>has enought api links with the hci-usb.c layer to be able to service all the alsa-driver api requirements.
By SCO layer you actually mean HCI core. Current SCO layer that we have is a simple raw socket interface
nothing else. So ALSA Bluetooth sound cart driver will completely current SCO layer.
>3) Once that all works, modify the other low level hardware drivers to work with it. e.g. bluecard_cs.c etc.
That's why we have to go though HCI core from the beginning. If we do it right all other drivers will just
work.
>The final result will be: -
>1) a small tool that will link a particular paired bluetooth device to a particular PCM device for alsa to work with. This tool will basically just take destination BTADDR and channel number to use, because alsa will have no knowledge of that sort of info. It will add a new sound card instance for each bluetooth device.
>2) alsa will just think that the bluetooth headset is a normal soundcard.
>3) This would make integration with current audio applications simple, because alsa supports the alsa-api as well as emulate the oss-api, so current audio applications would need no changes.
>4) We could even implement headset "in the vicinity" detection, so that when the headset transitioned from out of range to in range, your computer could say hello!
That's exactly what I had in mind. I was even going to start looking into ALSA architecture.
Max
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Marcel Holtmann wrote:
> Hi James,
>
>
>>The playback problem is a scheduling problem.
>>The "hci_usb_tx_complete" function uses the scheduler to kick off the
>>next transmission, but the scheduler is too slow, and the correct method
>>to use is getting the "hci_usb_tx_complete" function to retrieve the
>>next packet to send from a ring buffer, and send it immeadiately during
>>the "hci_usb_tx_complete" function. This is how the current usbaudio.c
>>does it, so it proves that this method will work.
>>So, I will need to implement a ring buffer.
>>At the same time I want to implement sound output via alsa, so I want to
>>make sure we have a good api to achieve that.
>>alsa requires certain information from the sound card (ring buffer
>>position etc.), and I will have to make sure that the information alsa
>>needs in available, by maybe adding new api calls through the sco layer
>>to the usb-hci.c layer. I think it would be a good idea to completely
>>separate the isoc(sound) urb path from the int/bulk/control urb path.
>>We also have the added complication that the alsa ring buffer is
>>composed of just sound samples, but the sco layer converts that to
>>packets with a header so the hci-usb.c layer has to deal with packets
>>instead of samples.
>>For 8 bit mono sound, SCO creates packets with 3 header bytes, and 24
>>sound samples. hci-usb.c then has to take each 27 byte packet and cut it
>>down into 3 slices each 9 bytes in length. All packet sizes and slice
>>sizes vary depending on 8/16 bits samples, and mono/stereo etc.
>
>
> the seperate handling of ISOC is a good idea. Max told me that ISOC
> URB's consumes USB bandwith and because of the fact that they are not
> needed all the time, we have to start and stop them dynamicly, if a SCO
> link is established or killed.
The start and stop of ISOC will happen in the alsa snd_pcm_trigger call.
The way an alsa application would work is: -
snd_pcm_open
snd_pcm_hwparam... (set format, # channels, buffer sizes etc.)
snd_pcm_prepare (recover from under/over runs.)
snd_pcm_trigger (actually start the stream with details from hwparm.)
Then during sound output, the application might call
snd_pcm_delay (returns difference between samples sent to the device,
and samples that have actually been played.)
snd_pcm_write (writes samples to ring buffer)
snd_pcm_drop ( emply ring buffer)
snd_pcm_close (stops the stream and frees resources.)
As you can see, most of these are almost possible with the current sco
interface, but snd_pcm_delay is definitly not present.
The actual function call to the alsa low level driver is
snd_pcm_get_postition().
So, my plan is to split the sco driver up a bit in accordance to your
suggestion. (Maybe I did not make myself clear on that point)
There will be a general section, that will handle calls for general sco
access(ring buffer, pointers into ring buffer management, adding sco
headers, handling sco connection connect/disconnect), and then there
will be other sections for application specific stuff. E.g. The network
interface, alsa interface, oss interface.
My reasoning here is that if one has the oss interface, one will not
need the alsa interface and visa versa, with the network interface being
optional.
It seems that alsa requires that all sound cards have ring buffers, and
pointers into these buffers. These buffers are read and the pointers
updated via callbacks from the sound hardware. It is this reason that I
suggest that all playback and capture via a SCO connection should be
handled with callbacks to the SCO layer from the HCI layer, with the SCO
layer handling the ring buffer, updating pointers into the ring buffer
and adding sco headers. Both alsa and oss have api calls to read these
buffer pointers, and there is no such pointer api in the current bluez
stack.
Then all other higher layer modules (oss, alsa, network) would interface
with this ring buffer. This would also have the benefit for providing
flow control for the application. I.E. If the ring buffer is full, it
blocks the write call. All ISOC connections are full-duplex,
configurable fixed bandwidth, so the ring buffer will always be emptied
at a fixed rate.
Another suggestion is to do all the alloc of memory and creation of
lists/queues at the snd_pcm_trigger stages, and not during tx/rx
complete callbacks.
>
> My current idea of handling this is that the hci_usb driver checks for
> SCO links in connection complete and disconnect complete events. Another
> idea is to add another HCI driver method (for example hdev->notify), so
> that the HCI core can notify the driver of special events or errors.
I have not really thought about connect/disconnect yet, apart from
linking it to snd_pcm_trigger/snd_pcm_close. I am concentrating of just
getting reliable sound playback over a sco connection. I.e The ring
buffer and rx/tx complete callbacks.
>
>
>>So, there is going to be quite a lot of manipulation of the sound
>>samples as they pass from alsa to the bluetooth device.
>>The questions I am still trying to decide are: -
>>1) When should the conversion from alsa ring buffer to packets take
>>place. So far the only workable solution I have come up with is that the
>>"hci_usb_tx_complete" makes a callback all the way to the sco layer, and
>>the sco layer grabs 24 bytes form the alsa ring buffer, adds it's header
>>and returns from the callback.
>>2) interface to alsa. I think this should happen just above the SCO
>>layer, but also ensuring that the SCO layer has enought api links with
>>the hci-usb.c layer to be able to service all the alsa-driver api
>>requirements.
>>3) Once that all works, modify the other low level hardware drivers to
>>work with it. e.g. bluecard_cs.c etc.
>
>
> The native integration of Bluetooth audio within Linux is one of the
> most wanted things. But we can't use ALSA for the 2.4 kernel, because it
> is not a part of the kernel. For the 2.6 this is no problem, but I also
> want to have support for OSS, because there will some people (like me)
> which still uses OSS.
Maybe split the sco driver into general helper api, and then separate
modules for network, oss, alsa type interfaces into user land.
>
> The integration of audio is not part of the Bluetooth drivers, because
> every Bluetooth HCI driver is only a transport driver which have to
> transport the HCI command, event, ACL and SCO data between the hardware
> and the HCI core layer. The SCO data would send from the HCI core
> through the hdev->send() callback and the driver can send the SCO data
> it gets from the hardware back with hci_recv_frame(). This means that
> all needed modifications for ALSA and OSS integration have to done in
> the HCI core or the SCO layer. And all other HCI drivers will still work
> with SCO like they do now.
The recv_frame() parts seem to work ok at the moment. (with some
modifications as outlined in a previous email)
The main problem is the send_frame() parts. hdev->send() is the wrong
thing to do for ISOC connections (one runs into scheduling problems,
buffer underruns and no flow control.). A callback method from the
hardware is much beter. (e.g. Give me X number of samples NOW!). This is
why I suggest a ring buffer and tx/rx complete callbacks from HCI to SCO
layer to update ring buffer pointers, and then the alsa or oss layer
above that.
I will do alsa first because there is much less work involved.
I know the callback/ringbuffer approach works well over usb, because
alsa has a usb-audio driver, and it works fine.
>
> Regards
>
> Marcel
>
>
Hi James,
> The playback problem is a scheduling problem.
> The "hci_usb_tx_complete" function uses the scheduler to kick off the
> next transmission, but the scheduler is too slow, and the correct method
> to use is getting the "hci_usb_tx_complete" function to retrieve the
> next packet to send from a ring buffer, and send it immeadiately during
> the "hci_usb_tx_complete" function. This is how the current usbaudio.c
> does it, so it proves that this method will work.
> So, I will need to implement a ring buffer.
> At the same time I want to implement sound output via alsa, so I want to
> make sure we have a good api to achieve that.
> alsa requires certain information from the sound card (ring buffer
> position etc.), and I will have to make sure that the information alsa
> needs in available, by maybe adding new api calls through the sco layer
> to the usb-hci.c layer. I think it would be a good idea to completely
> separate the isoc(sound) urb path from the int/bulk/control urb path.
> We also have the added complication that the alsa ring buffer is
> composed of just sound samples, but the sco layer converts that to
> packets with a header so the hci-usb.c layer has to deal with packets
> instead of samples.
> For 8 bit mono sound, SCO creates packets with 3 header bytes, and 24
> sound samples. hci-usb.c then has to take each 27 byte packet and cut it
> down into 3 slices each 9 bytes in length. All packet sizes and slice
> sizes vary depending on 8/16 bits samples, and mono/stereo etc.
the seperate handling of ISOC is a good idea. Max told me that ISOC
URB's consumes USB bandwith and because of the fact that they are not
needed all the time, we have to start and stop them dynamicly, if a SCO
link is established or killed.
My current idea of handling this is that the hci_usb driver checks for
SCO links in connection complete and disconnect complete events. Another
idea is to add another HCI driver method (for example hdev->notify), so
that the HCI core can notify the driver of special events or errors.
> So, there is going to be quite a lot of manipulation of the sound
> samples as they pass from alsa to the bluetooth device.
> The questions I am still trying to decide are: -
> 1) When should the conversion from alsa ring buffer to packets take
> place. So far the only workable solution I have come up with is that the
> "hci_usb_tx_complete" makes a callback all the way to the sco layer, and
> the sco layer grabs 24 bytes form the alsa ring buffer, adds it's header
> and returns from the callback.
> 2) interface to alsa. I think this should happen just above the SCO
> layer, but also ensuring that the SCO layer has enought api links with
> the hci-usb.c layer to be able to service all the alsa-driver api
> requirements.
> 3) Once that all works, modify the other low level hardware drivers to
> work with it. e.g. bluecard_cs.c etc.
The native integration of Bluetooth audio within Linux is one of the
most wanted things. But we can't use ALSA for the 2.4 kernel, because it
is not a part of the kernel. For the 2.6 this is no problem, but I also
want to have support for OSS, because there will some people (like me)
which still uses OSS.
The integration of audio is not part of the Bluetooth drivers, because
every Bluetooth HCI driver is only a transport driver which have to
transport the HCI command, event, ACL and SCO data between the hardware
and the HCI core layer. The SCO data would send from the HCI core
through the hdev->send() callback and the driver can send the SCO data
it gets from the hardware back with hci_recv_frame(). This means that
all needed modifications for ALSA and OSS integration have to done in
the HCI core or the SCO layer. And all other HCI drivers will still work
with SCO like they do now.
Regards
Marcel
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