New bluetooth-headset release 20061109 : nickname 'dogfood' ; -)

Regarding the kernel patches, you know I've taken a different approach. I believe that what I posted is simpler and more reliable as it doesn't depend timers. The flow control approach avoids the possibility of getting out of sync with the dongle.

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Regarding the kernel patches, you know I've taken a different approach. I believe that what I posted is simpler and more reliable as it doesn't depend timers. The flow control approach avoids the possibility of getting out of sync with the dongle.

fyi, I talked to Marcel about this and he likes solving it at a higher level so the transports (usb/uart/sdio) don't have to each have their own solution. Maybe he could articulate it better...

Hi Brad,

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Regarding the kernel patches, you know I've taken a different approach. I believe that what I posted is simpler and more reliable as it doesn't depend timers. The flow control approach avoids the possibility of getting out of sync with the dongle.

fyi, I talked to Marcel about this and he likes solving it at a higher level so the transports (usb/uart/sdio) don't have to each have their own solution. Maybe he could articulate it better...

I am not against using flow control, but we must be really careful if it supported or not. While for ACL it is mandatory, the SCO channel can be used without it. However even the use of flow control on SCO is a job for the Bluetooth core and no driver specific one. All Bluetooth drivers are transport drivers. They have no intelligence whatsoever and they are not interfering the HCI data. If they need to know some specific details about changes in the core then the notify() callback is the right place and if they need a special setup, then a quirk should be used. Other than that, they are plain stupid and only moving HCI packets to the hardware and back.

So from my understanding the high resolution timer are a good choice to submit SCO packets to the hardware. In addition we can enable the flow control for SCO to have more control over the hardware. However please keep in mind that the enabling flow control means for traffic on the ACL links and so you might see a downgrade in bandwidth. So from my current point of view, the flow control stuff must be optional.

Regards

Marcel

Quoted 11 lines

I am not against using flow control, but we must be really careful if it supported or not. While for ACL it is mandatory, the SCO channel can be used without it. However even the use of flow control on SCO is a job for the Bluetooth core and no driver specific one. All Bluetooth drivers are transport drivers. They have no intelligence whatsoever and they are not interfering the HCI data. If they need to know some specific details about changes in the core then the notify() callback is the right place and if they need a special setup, then a quirk should be used. Other than that, they are plain stupid and only moving HCI packets to the hardware and back.

Quoted 6 lines

So from my understanding the high resolution timer are a good choice to submit SCO packets to the hardware. In addition we can enable the flow control for SCO to have more control over the hardware. However please keep in mind that the enabling flow control means for traffic on the ACL links and so you might see a downgrade in bandwidth. So from my current point of view, the flow control stuff must be optional.

The problem with using timers is that they are not synchronized with the bluetooth controller (dongle). This can cause drift after a while leading to underrun condition on the controller. This will cause pops or other audio artifacts. So this solution will always have a design flaw. I don't find this acceptable.

Let me address some of your objections to using the flow control:

1. extra bandwith - this is the price to pay for synchronization. In the case of USB no additional messages are sent and overhead is part of the USB isosynchronous transport.

2. some dongles may not support flow control - it's true that flow control can be turned off for synchronous traffic but it' s not clear to me that this is optional for controllers that support SCOs. We're really talking about UART or other interfaces. Can anyone provide an example where it's NOT supported?

3. Transport drivers are dumb - this is a problem with the existing drivers that should be addressed. They need to differentiate between different types of traffic otherwise it's quite easy to starve the synchronous channel with ACL data. In fact, the current architecture can't support multiple SCOs reliably because of this. At the very least, separate queues must be used for synchronous and other traffic.

Hi Jose,

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I am not against using flow control, but we must be really careful if it supported or not. While for ACL it is mandatory, the SCO channel can be used without it. However even the use of flow control on SCO is a job for the Bluetooth core and no driver specific one. All Bluetooth drivers are transport drivers. They have no intelligence whatsoever and they are not interfering the HCI data. If they need to know some specific details about changes in the core then the notify() callback is the right place and if they need a special setup, then a quirk should be used. Other than that, they are plain stupid and only moving HCI packets to the hardware and back.

Quoted 7 lines

So from my understanding the high resolution timer are a good choice to submit SCO packets to the hardware. In addition we can enable the flow control for SCO to have more control over the hardware. However please keep in mind that the enabling flow control means for traffic on the ACL links and so you might see a downgrade in bandwidth. So from my current point of view, the flow control stuff must be optional.

Quoted 6 lines

The problem with using timers is that they are not synchronized with the bluetooth controller (dongle). This can cause drift after a while leading to underrun condition on the controller. This will cause pops or other audio artifacts. So this solution will always have a design flaw. I don't find this acceptable.

I don't see the synchronization as a problem, because once SCO traffic is on, we get a PCM stream back from the chip we can use this one as a synchronization source.

Quoted 6 lines

Let me address some of your objections to using the flow control:

1. extra bandwith - this is the price to pay for synchronization. In the case of USB no additional messages are sent and overhead is part of the USB isosynchronous transport.

Wrong. We always have additional HCI commands and events if SCO flow control has been enabled. This is no difference from the actual transport you use. The only difference for USB is that they are on a different interface of the USB device.

Quoted 6 lines

2. some dongles may not support flow control - it's true that flow control can be turned off for synchronous traffic but it' s not clear to me that this is optional for controllers that support SCOs. We're really talking about UART or other interfaces. Can anyone provide an example where it's NOT supported?

It is optional no matter if it is UART, USB or any other transport. This is has nothing to do with the actual hardware interface.

Quoted 8 lines

3. Transport drivers are dumb - this is a problem with the existing drivers that should be addressed. They need to differentiate between different types of traffic otherwise it's quite easy to starve the synchronous channel with ACL data. In fact, the current architecture can't support multiple SCOs reliably because of this. At the very least, separate queues must be used for synchronous and other traffic.

I don't see what you are actually talking about. We have separate queues for ACL and SCO data, because the queues are connection specific. What the actual driver is doing is up to the driver. However the Bluetooth hardware drivers are transport drivers and the core has to be fully agnostic from any hardware specific implementation of the transports.

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I am not against using flow control, but we must be really careful if it supported or not. While for ACL it is mandatory, the SCO channel can be used without it. However even the use of flow control on SCO is a job for the Bluetooth core and no driver specific one. All Bluetooth drivers are transport drivers. They have no intelligence whatsoever and they are not interfering the HCI data. If they need to know some specific details about changes in the core then the notify() callback is the right place and if they need a special setup, then a quirk should be used. Other than that, they are plain stupid and only moving HCI packets to the hardware and back.

Quoted 7 lines

So from my understanding the high resolution timer are a good choice to submit SCO packets to the hardware. In addition we can enable the flow control for SCO to have more control over the hardware. However please keep in mind that the enabling flow control means for traffic on the ACL links and so you might see a downgrade in bandwidth. So from my current point of view, the flow control stuff must be optional.

Quoted 6 lines

The problem with using timers is that they are not synchronized with the bluetooth controller (dongle). This can cause drift after a while leading to underrun condition on the controller. This will cause pops or other audio artifacts. So this solution will always have a design flaw. I don't find this acceptable.

Quoted 5 lines

I don't see the synchronization as a problem, because once SCO traffic is on, we get a PCM stream back from the chip we can use this one as a synchronization source.

I don't see this as an acceptable solution. First, the current code makes it very easy for a trivial program to cause Linux to panic. Second, using received data to synchronize puts the burden at the application layer when this should be a driver issue. Third, this will never scale to asymmetric eSCO connections.

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Let me address some of your objections to using the flow control:

1. extra bandwith - this is the price to pay for synchronization. In the case of USB no additional messages are sent and overhead is part of the USB isosynchronous transport.

Quoted 6 lines

Wrong. We always have additional HCI commands and events if SCO flow control has been enabled. This is no difference from the actual transport you use. The only difference for USB is that they are on a different interface of the USB device.

In the case of USB, the flow control messages are sent to the bluetooth hci core by hci_usb; this is done when the USB layer has acknowledged the transferred. No additional messages are sent by the controller. Whether you take advantage of the USB layer or not, the USB overhead is always there.

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2. some dongles may not support flow control - it's true that flow control can be turned off for synchronous traffic but it' s not clear to me that this is optional for controllers that support SCOs. We're really talking about UART or other interfaces. Can anyone provide an example where it's NOT supported?

Quoted 3 lines

It is optional no matter if it is UART, USB or any other transport. This is has nothing to do with the actual hardware interface.

It's optional in the sense that an application may not need it. A custom profile may be sending non-PCM data and deal with it. That's not to say that it's optional for a controller if it supports SCO. For USB there's flow control at that layer.

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3. Transport drivers are dumb - this is a problem with the existing drivers that should be addressed. They need to differentiate between different types of traffic otherwise it's quite easy to starve the synchronous channel with ACL data. In fact, the current architecture can't support multiple SCOs reliably because of this. At the very least, separate queues must be used for synchronous and other traffic.

Quoted 7 lines

I don't see what you are actually talking about. We have separate queues for ACL and SCO data, because the queues are connection specific. What the actual driver is doing is up to the driver. However the Bluetooth hardware drivers are transport drivers and the core has to be fully agnostic from any hardware specific implementation of the transports.

The scheduling in hci_core.c will send all acl data before sco. This prevents the driver from having access to the SCO data in a timely manner. Then the hci_usb driver puts the packets in one transmit queue.

Before going too far with technical details, I think it's worth understanding what level of Bluetooth compatibility is desired. The current state is adequate but not robust (easy to panic). Perhaps my expectations are higher that what the community wants. Of course, you could argue that other environments or solutions aren't much better, and this maybe true. I don't mean to cause problems; I just want a better support for SCO/eSCO.

Hi Fabien,

I have a minor suggestion regarding the binding of the unix socket in daemon.c. Currently, the socket name registered contains nul characters. It would be better to register the name without the extra fill for monitoring applications.

Jose

../cvs/alsa-plugin-sco/headsetd/new/daemon.c 2006-09-01 renamed from daemon.c 2006-05-18 10:30:06.000000000 -0400 +0 -0

19:18:04.000000000 -0400

../cvs/alsa-plugin-sco/headsetd/new/daemon.c 2006-09-01 renamed from daemon.c 2006-05-18 10:30:06.000000000 -0400 +1 -1

@@ -73,7 +73,7 @@
     struct sockaddr_un  pcm_srv_sock = {
         AF_UNIX, PCM_SERVER_SOCKET
     };
-    if(bind(_appl_srv_sockfd, (struct sockaddr *)&pcm_srv_sock, 
 sizeof(pcm_srv_sock)) != 0) {
+    if(bind(_appl_srv_sockfd, (struct sockaddr *)&pcm_srv_sock, 
 __SOCKADDR_COMMON_SIZE+sizeof(PCM_SERVER_SOCKET)-1) != 0) {
             syslog(LOG_ERR, "bind(_appl_srv_sockfd): %s", strerror(errno));

         goto error;   
     }

../cvs/alsa-plugin-sco/headsetd/new/daemon.c 2006-09-01 renamed from daemon.c 2006-05-18 10:30:06.000000000 -0400 +1 -1

@@ -96,7 +96,7 @@
     struct sockaddr_un  ctl_srv_sock = {
         AF_UNIX, CTL_SERVER_SOCKET
     };
-    if(bind(_appl_ctlsrv_sockfd, (struct sockaddr *)&ctl_srv_sock, 
 sizeof(ctl_srv_sock)) != 0) {
+    if(bind(_appl_ctlsrv_sockfd, (struct sockaddr *)&ctl_srv_sock, 
 __SOCKADDR_COMMON_SIZE+sizeof(CTL_SERVER_SOCKET)-1) != 0) {
             syslog(LOG_ERR, "bind(_appl_ctlsrv_sockfd): %s", 

strerror(errno));
         goto error2;   
     }

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Hi Fabien,

Please take a look at file /proc/net/unix. It lists all opened sockets. If headsetd is running, it's easy to tell because that is the only one that has a string of nul characters following the name. My patch fixes that.

Jose

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