[Bluez-devel] Maintain Bluetooth Connections

[Bluez-devel] Maintain Bluetooth Connections

[Williams, Richard]

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Greetings Marcel,

I have a small, wearable computer, battery powered, of course. The
X-scale processor is connected to the BT radio through a serial port and
is the master in a small network of BT devices. All this works very
well. This is running Linux 2.6 with the latest patches.

During idle periods, to save power, I want to suspend the main
microprocessor. The BT radio is powered from a separate circuit. For
now, before I suspend the micro, I close all the connections, and
perform a "bluetooth stop". When the micro wakes up, the micro does a
"bluetooth start" and then reestablishes the connections to the
peripheral devices. This does work, but it takes some time. I would like
to have the BT network recover as quickly as possible.

Is it possible to instruct the BT radio to autonomously maintain the
established connections, even though the microprocessor has been
suspended ?  So that when the main processor wakes up, the BT network is
still there. I don't know how much of the connection "keep alive"
function is performed by the Bluez stack.

Thank you, as usual for all your help.

Best Regards,

Rich

----------------------------
Richard B. Williams
Vitronics, Inc.
An MTC Technologies Company
3 Corbett Way
Eatontown, NJ 07724-2262
732-389-0244 x29
Richard.Williams@mtctechnologies.com



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Re: [Bluez-devel] Maintain Bluetooth Connections

[Marcel Holtmann]

Hi Richard,

> I have a small, wearable computer, battery powered, of course. The
> X-scale processor is connected to the BT radio through a serial port
> and is the master in a small network of BT devices. All this works
> very well. This is running Linux 2.6 with the latest patches.
> 
> During idle periods, to save power, I want to suspend the main
> microprocessor. The BT radio is powered from a separate circuit. For
> now, before I suspend the micro, I close all the connections, and
> perform a "bluetooth stop". When the micro wakes up, the micro does a
> "bluetooth start" and then reestablishes the connections to the
> peripheral devices. This does work, but it takes some time. I would
> like to have the BT network recover as quickly as possible.
> 
> Is it possible to instruct the BT radio to autonomously maintain the
> established connections, even though the microprocessor has been
> suspended ?  So that when the main processor wakes up, the BT network
> is still there. I don't know how much of the connection "keep alive"
> function is performed by the Bluez stack.

not that I know and there is no keep alive in the BlueZ stack. Actually
we don't support idle disconnect and even not automatic sniff mode. The
latter one is on my todo list.

Regards

Marcel




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Re: [Bluez-devel] Maintain Bluetooth Connections

[Peter Wippich]

Hi Richard,

just some crude thoughts about this:

What happens if one of the remote devices wants to send some data to the
PDA ?? Or can you make sure that this will not happen ?? If it can happen
you need some sort of wakeup on your host. If the host can wake up on
serial line activity this is fine, but as far as I remember this is not
possible with an X-scale.

If you are sure that the above will not cause you problems you could put
all active connections into park mode, which will allow the BT chip to
save a lot of power. However, you have to remember the state of each
active connection to unpark it once your host wakes up. Because you have
to remeber te connections states a bluetooth stop / start is not an
option. You have to add (I don't know if there already is something, but
from Marcels answer I think it is not) power management at least to the
HCI layer which parks the slaves if you enter low power state and unparks them
when you come back.

Good luck !!!

Peter

On Thu, 10 Feb 2005, Williams, Richard wrote:

> Greetings Marcel,
>
> I have a small, wearable computer, battery powered, of course. The
> X-scale processor is connected to the BT radio through a serial port and
> is the master in a small network of BT devices. All this works very
> well. This is running Linux 2.6 with the latest patches.
>
> During idle periods, to save power, I want to suspend the main
> microprocessor. The BT radio is powered from a separate circuit. For
> now, before I suspend the micro, I close all the connections, and
> perform a "bluetooth stop". When the micro wakes up, the micro does a
> "bluetooth start" and then reestablishes the connections to the
> peripheral devices. This does work, but it takes some time. I would like
> to have the BT network recover as quickly as possible.
>
> Is it possible to instruct the BT radio to autonomously maintain the
> established connections, even though the microprocessor has been
> suspended ?  So that when the main processor wakes up, the BT network is
> still there. I don't know how much of the connection "keep alive"
> function is performed by the Bluez stack.
>
> Thank you, as usual for all your help.
>
> Best Regards,
>
> Rich
>
> ----------------------------
> Richard B. Williams
> Vitronics, Inc.
> An MTC Technologies Company
> 3 Corbett Way
> Eatontown, NJ 07724-2262
> 732-389-0244 x29
> Richard.Williams@mtctechnologies.com
>
>
>

|	Peter Wippich 			Voice: +49 30 46776411		|
|	G&W Instruments GmbH		fax:   +49 30 46776419		|
|	Gustav-Meyer-Allee 25, Geb. 12	Email: pewi@gw-instruments.de	|
|	D-13355 Berlin  / Germany					|




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RE: [Bluez-devel] Maintain Bluetooth Connections

[Williams, Richard]

Peter raises some interesting possibilities:

>What happens if one of the remote devices wants to send some data to
the PDA ??=20
>Or can you make sure that this will not happen ?? If it can happen you
need some=20
>sort of wakeup on your host. If the host can wake up on serial line
activity this=20
>is fine, but as far as I remember this is not possible with an X-scale.

- suppose the master has suspended and its BT radio is still awake
maintaining=20
the network integrity. If another new device does something as simple as
hci scan,=20
how will the BT device of the suspended processor behave? I suspect that
the BT=20
device will be unable to handle this and will probably do something
ugly.


>If you are sure that the above will not cause you problems you could
put=20
>all active connections into park mode, which will allow the BT chip to
save=20
>a lot of power. However, you have to remember the state of each active=20
>connection to unpark it once your host wakes up. Because you have to
remeber=20
>te connections states a bluetooth stop / start is not an option. You
have to=20
>add (I don't know if there already is something, but from Marcels
answer I=20
>think it is not) power management at least to the HCI layer which parks
the=20
>slaves if you enter low power state and unparks them when you come
back.

Your idea to park the connections is worth pursuing. My applications can

park/un-park during the X-scale suspend/wakeup sequence. All of my
applications=20
"know" about that a system-wide suspend is taking place, so they can do
what's=20
necessary. I'm not sure that this is what I would ultimately want to do,
but
Its worth hacking something together to see if it works at all.
I'm not sure if my peripheral devices support park mode, but that's=20
worth looking into.

Thanks for the idea.

Rich
----------------------------
Richard B. Williams
Vitronics, Inc.
An MTC Technologies Company
3 Corbett Way
Eatontown, NJ 07724-2262
732-389-0244 x29
Richard.Williams@mtctechnologies.com





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RE: [Bluez-devel] Maintain Bluetooth Connections

[Peter Wippich]

Hi Richard,

On Thu, 10 Feb 2005, Williams, Richard wrote:

> - suppose the master has suspended and its BT radio is still awake
> maintaining
> the network integrity. If another new device does something as simple as
> hci scan,
> how will the BT device of the suspended processor behave? I suspect that
> the BT
> device will be unable to handle this and will probably do something
> ugly.

It may also be a good idea to disable page / inquiry scan on the local
radio.

Ciao,

Peter



|	Peter Wippich 			Voice: +49 30 46776411		|
|	G&W Instruments GmbH		fax:   +49 30 46776419		|
|	Gustav-Meyer-Allee 25, Geb. 12	Email: pewi@gw-instruments.de	|
|	D-13355 Berlin  / Germany					|




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