[PD-dev] libpd blues

[Tom Schouten]

hi all,

i'm libifying pd and ran into some problems. i decided to
jump to the problem uninformed, as usual, so.. :))

my goal is to have a (gui-less) pd as a callback in another
program. currently i'm happy if it just runs in packet forth
as part of the VM zoo.

it should 'behave' in a sense that it should not execute any 
blocking calls, and leave the time keeping to the host program.
the idea is that m_scheduler_tick() is called for each
64 audio sample block, and all the other things that need to
be done should be executed in this tick method.

i got most of it running, only the time keeping seems to do
something else than i think it does. this is what i sort of
works for me:

-- in m_sched.c, i reduced the scheduler to:


void m_scheduler_init(void){
    sys_time_per_dsp_tick = (TIMEUNITPERSEC) *
        ((double)sys_schedblocksize) / sys_dacsr;

    post("timeunitspersec = %f", (float)TIMEUNITPERSEC);
    post("sys_schedblocksize = %f", (float)sys_schedblocksize);
    post("sys_dacsr = %f", (float)sys_dacsr);

    sys_clearhist();         // not used
    sys_initmidiqueue();     // not used
}

int m_scheduler_tick(void){
    sys_setmiditimediff(0, 1e-6 * sys_schedadvance);
    sched_tick(sys_time + sys_time_per_dsp_tick * 8.0);
    sys_pollmidiqueue();
    sys_microsleep(1);  // poll file descriptors
}


-- when i link libpd to pd.c (mini-pd host) using this:

int main(int argc, char **argv)
{
    int retval;
    if ((retval = sys_main(argc, argv))) return retval;

    m_scheduler_init();
    while(1){
	m_scheduler_tick();
	//usleep(1);
    }
}


--

i added a new audio driver, which is just fills in
some values to keep pd happy, but the scheduler does
not call send_dacs. (the idea is that the tick method
does the sys_soundin -> sys_soundout step)

now, the strange things are:

* the 8.0 i needed to add in m_scheduler_tick()
maybe there's a global variable i missed somewhere?

* sys_microsleep(1) works, but sys_microsleep(0) does not
this seems strange, since it only polls?

* if i add the usleep in main(), timing is off again.
this seems completely strange to me


all very distorted and i'm probably missing something obvious.. 

so, the question is: how do i update pd time properly
if i run pd synchronous by calling something like m_scheduler_tick() ?

cheers
tom