[Gta04-owner] QtMoko v38 for GTA04 with suspend and GSM calls

Dr. H. Nikolaus Schaller hns at goldelico.com
Tue Jan 31 12:13:51 CET 2012

Am 31.01.2012 um 12:01 schrieb Dr. H. Nikolaus Schaller:

> Hi Radek,
> Am 29.01.2012 um 14:45 schrieb Radek Polak:
>> There is still problems with GSM calls that other site hears echo and you will 
>> need to set silent profile in Qtmoko's settings to have sound in incoming call.
> while testing some boards with our arecord | aplay scripts I observed
> that the ringing tone of the phone being called is transmitted after
> several seconds.
> Let me try an explanation:
> * arecord on the microphone starts immediately filling the pipe
> * aplay towards the modem does not start before it gets clocked
> * this is only when the connection is accepted
> * this may delay up to 5 seconds
> * arecord on the modem does start at the same moment
> * and aplay on the phone sees an empty pipe until then
> So, the filling level of the pipe 
> microphone -> CPU -> pipe -> CPU -> modem
> is up to 5 seconds with sound - before the phone call is
> established. This includes recording the ringing tone of
> my landline phone :)
> Since supplier and consumer speeds are both 8 kHz, the
> pipe filling level remains constant, i.e. the same delay.
> So a solution would be to use a pipe with limited size
> (does not exist) or write our own daemon to spawn and
> communicate with all arecord/aplay subprocesses and
> discard all microphone data until the first byte from the
> modem arrives. It does not need to be complex, just
> forking 4 processes and setting up a select(). Maybe,
> the code of femtocom.c could even be a start. If I find
> some time before/during FODEM I could give it a try...
> Hope this gives an idea...
> Nikolaus

Here some quick hack (untested and incomplete):

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