[PD] Help with writing externals

[thewade]

Thanks for the help Yves and IOhannes,

I tried your suguestion of 5, as relates to number of parameters, not to count of the sp array, which is what I thought at first. Your suguestion makes more sense.

I still get a segmentation fault though, after I turn on audio processing.

I looked at the page IOhannes pointed me too, and it looks like the only thing I dont do is step through all the samples in the block (while n-- busness). Could this be hats causing my break?

Is the error message I get about fftbin_tilde_dsp really about fftbin_tilde_perform because of this treatment of the sampleblock?

All I want to do is take one value, as specified by my seccond inlet, out of the whole sample block in the first inlet, and spit that out the outlet. I do this as below, in the perform function.

Below is my perform function, the gdb output, and my dsp function.

Thanks for the help again!
-thewade

/*-----------fftbin\'s perform function-------------------*/
t_int *fftbin_tilde_perform(t_int *w)
{
  t_fftbin  *ref = (t_fftbin *)(w[1]);         //data structure
  t_sample  *in1 = (t_sample *)(w[2]);         //fft~ output
  int        in2 = (int)(w[3]);                //bin number
  t_sample  *out = (t_float *)(w[4]);          //outlet
  int        n   = (int)(w[5]);                //number of samples in block

  int bin         = in2;                       //get bin number
  if (bin<0) bin  = 0;                         //clip bin to between 0 and n-1
  if (bin>=n) bin = n-1;
  ref->x_bin      = bin;                       //set datstructure
  ref->x_f        = (t_float)*in1+ref->x_bin;  //again, set datastructure
  *out            = ref->x_f;                  //output float value of bin

  return (w+6);
}
/*-------------------------------------------------------*/

/*---------------gdb debug information-------------------*/
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 1073855264 (LWP 1254)]
0x414b197b in fftbin_tilde_dsp () from /home/wade/pd/general/fftbin~.pd_linux
(gdb) where
#0  0x414b197b in fftbin_tilde_dsp () from /home/wade/pd/general/fftbin~.pd_linux
#1  0x082321d0 in ?? ()
#2  0x082312d8 in ?? ()
#3  0x08231234 in ?? ()
#4  0x082321d0 in ?? ()
#5  0x0809daad in ugen_doit (dc=0x82312d8, u=0xffffffff) at d_ugen.c:750
#6  0x0809ea46 in ugen_done_graph (dc=0x8231eb8) at d_ugen.c:1007
#7  0x08230a20 in ?? ()
#8  0x08231eb8 in ?? ()
#9  0x00000001 in ?? ()
#10 0x00000001 in ?? ()
#11 0x00000000 in ?? ()
/*-------------------------------------------------------*/

/*------------------------fftbin dsp function------------*/
void fftbin_tilde_dsp(t_fftbin *ref, t_signal **sp)
{
  dsp_add(fftbin_tilde_perform, 5, ref,
          sp[0]->s_vec, sp[1]->s_vec, sp[2]->s_vec, sp[0]->s_n);
}
/*-------------------------------------------------------*/