Re: [LAD] Adding a c timer to Kluppe

On 04/21/2010 03:43 AM, Niels Mayer wrote:
> I don't know anything about the kluppe code, but are the underlying
> libraries you're using re-entrant? My brief perusal
> of your code raised red-flags due to use of signal(2) and alarm(2).
> Execution ends up jumping around asynchronously&&indeterminately, in
> audio code or threads that probably should never have that happen. For
> example. lets say you had a piece of code that needed to execute
> within a certain amount of time in order to generate a data-stream w/o
> interruption -- lowlevel code that never expected to be jumped out of
> to take care of some random "application level" business that it
> shouldn't need to concern itself over.
>
> This probably requires an event-driven architecture, where everything
> is driven by IO. Looked at that way, a timer timing out is just
> another thing to select(2) on; as long as your code doesn't block on
> I/O, you never need to worry about reentrancy.
>

Thanks for taking the time to ponder this one.

Based on what I understand from your suggestion above I have changed the
code to the following. However I still get the buzz during the pause
period at the end of the loop. So it seems that the audio stream is
being output with non zero values even though I have expressly set it to
be silent prior to the select/sleep kicking in. If anyone has thoughts
on why this is happening the way that it is I would appreciate your insight.

                     struct timeval time, pause;

                     pause.tv_sec = data->playbackdelay;
                     pause.tv_usec = 0;

                      looperdata_set_vol(data,0);

                     (void) select(0, 0, 0, 0, &pause);
                 // sleep((int)data->playbackdelay);

                     looperdata_set_vol(data,vol);

                     /* return to start of loop */
                     data->playindex += data->loopstart - data->loopend;

Patrick Shirkey
Boost Hardware Ltd

> Niels
> http://nielsmayer.com
>
> On Tue, Apr 20, 2010 at 6:12 AM, Patrick Shirkey
> <pshirkey@email-addr-hidden <mailto:pshirkey@email-addr-hidden>> wrote:
>
> Hi,
>
> I'm trying to add a threaded timer to kluppes looperdata.c
> looperdata_calc_sample_stereo function so that I can add a delayed
> restart to the loop process.
>
> Can anyone tell me why the "while" statement in the following code
> locks
> up the audio stream for the loop it is being run on? I end up with a
> buzz throughout the delay period instead of a nice quiet delay period.
>
>
>
> #include <stdlib.h>
> #include <signal.h>
> #include <stdio.h>
>
> /* This flag controls termination of the main loop. */
> volatile sig_atomic_t isdelay_countdown = 1;
>
> /* The signal handler just clears the flag and re-enables itself. */
> void catch_alarm (int sig){
> isdelay_countdown = 0;
> signal (sig, catch_alarm);
> }
>
>
>
> vol = data->vol;
>
> if(data->playbackdelay > 0){
>
> /* Establish a handler for SIGALRM signals. */
> signal (SIGALRM, catch_alarm);
>
> isdelay_countdown = 1;
>
> /* Call alarm to countdown length of
> playbackdelay */
> alarm ((int)data->playbackdelay);
>
> /* Check the flag once in a while to see when to
> quit. */
> while(isdelay_countdown){
> looperdata_set_vol(data,0);
> data->isplaying = 0;
> }
>
>
> }
>
> /* return to start of loop */
>
> looperdata_set_vol(data,vol);
> data->isplaying = 1;
> data->playindex += data->loopstart -
> data->loopend;
>
>
>
>
> --
> Patrick Shirkey
> Boost Hardware Ltd
>
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Received on Wed Apr 21 04:15:03 2010