The Alternative Csound Reference Manual
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# Adding your own Cmodules to Csound

If the existing Csound generators do not suit your needs, you can write your own modules in C and add them to the run-time system. When you invoke Csound on an orchestra and score file, the orchestra is first read by a table-driven translator 'otran' and the instrument blocks converted to coded templates ready for loading into memory by 'oload' on request by the score reader. To use your own C-modules within a standard orchestra you need only add an entry in otran's table and relink Csound with your own code.

The translator, loader, and run-time monitor will treat your module just like any other provided you follow some conventions. You need a structure defining the inputs, outputs and workspace, plus some initialization code and some perf-time code. Let's put an example of these in two new files, newgen.h and newgen.c:

    /* newgen.h  -  define a structure */
    typedef struct
    {
      OPDS h;  /* required header */
      float *result, *istrt, *incr, *itime, *icontin; /* addr outarg, inargs */
      float curval, vincr;  /* private dataspace */
      long countdown;  /* ditto */
    } RMP;

    /* newgen.c -  init and perf code */
    #include "cs.h"
    #include "newgen.h"

    void rampset (RMP * p)  /* at note initialization: */
    {
      if (*p - icontin == 0.)
        p - curval = *p - istrt;  /* optionally get new start value */
      p - vincr = *p - incr / esr;  /* set s-rate increment per sec. */
      p - countdown = *p - itime * esr;  /* counter for itime seconds */
    }

    void ramp (RMP * p)  /* during note performance: */
    {
      float *rsltp = p - result;  /* init an output array pointer */
      int nn = ksmps;  /* array size from orchestra */
      do
        {
          *rsltp++ = p - curval;  /* copy current value to output */
          if (--p - countdown = 0)  /* for the first itime seconds, */
            p - curval += p - vincr;  /* ramp the value */
        }
      while (--nn);
    }

Now we add this module to the translator table entry.c, under the opcode name rampt:

    #include "newgen.h"

    void rampset(), ramp();

    /*   opcode    dspace  thread    outarg    inargs      isub       ksub     asub    */

    { "rampt",  S(RMP),  5,        "a",      "iiio",     rampset,   NULL,    ramp  },

Finally we relink Csound to include the new module. If your Csound installation has created a libcsound.a, you can do this by typing

    cc -o mycsound newgen.c entry.c -lcsound -lX11 -lm
    (X11 if included at installation)

Else copy *.c, *.h and Makefile from the Csound sources, add newgen.o to the Makefile list OBJS, add newgen.h as a dependency for entry.o, and a new dependency 'newgen.o: newgen.h', then run 'make CSound'. If your host is a Macintosh, simply add newgen.h and newgen.c to one of the segments in the Csound Project, and invoke the C compiler.

The above actions have added a new generator to the Csound language. It is an audio-rate linear ramp function which modifies an input value at a user-defined slope for some period. A ramp can optionally continue from the previous note's last value. The Csound manual entry would look like:

    ar rampt istart, islope, itime [, icontin]

istart -- beginning value of an audio-rate linear ramp. Optionally overridden by a continue flag.

islope -- slope of ramp, expressed as the y-interval change per second.

itime -- ramp time in seconds, after which the value is held for the remainder of the note.

icontin (optional) -- continue flag. If zero, ramping will proceed from input istart . If non-zero, ramping will proceed from the last value of the previous note. The default value is zero.

The file newgen.h includes a one-line list of output and input parameters. These are the ports through which the new generator will communicate with the other generators in an instrument. Communication is by address, not value, and this is a list of pointers to floats. There are no restrictions on names, but the input-output argument types are further defined by character strings in entry.c (inargs, outargs). Inarg types are commonly x, a, k, and i, in the normal Csound manual conventions; also available are o (optional, defaulting to 0), p (optional, defaulting to 1). Outarg types include a, k, i and s (asig or ksig). It is important that all listed argument names be assigned a corresponding argument type in entry.c. Also, i-type args are valid only at initialization time, and other-type args are available only at perf time. Subsequent lines in the RMP structure declare the work space needed to keep the code re-entrant. These enable the module to be used multiple times in multiple instrument copies while preserving all data.

The file newgen.c contains two subroutines, each called with a pointer to the uniquely allocated RMP structure and its data. The subroutines can be of three types: note initialization, k-rate signal generation, a-rate signal generation. A module normally requires two of these initialization, and either k-rate or a-rate subroutines which become inserted in various threaded lists of runnable tasks when an instrument is activated. The thread-types appear in entry.c in two forms: isub, ksub and asub names; and a threading index which is the sum of isub=1, ksub=2, asub=4. The code itself may reference global variables defined in cs.h and oload.c, the most useful of which are:

      extern  OPARMS  O ;          float   esr
          user-defined sampling rate   float   ekr
          user-defined control rate    float   ensmps
          user-defined ksmps           int     ksmps
          user-defined ksmps           int     nchnls
          user-defined nchnls          int     O.odebug
          command-line -v flag         int     O.msglevel
          command-line -m level        float   pi, twopi    obvious
          constants                    float   tpidsr    twopi / esr float
          sstrcod                      special code for string arguments

# Function tables

To access stored function tables, special help is available. The newly defined structure should include a pointer

    FUNC        *ftp;

initialized by the statement

    ftp = ftpfind(p-ifuncno);

where float *ifuncno is an i-type input argument containing the ftable number. The stored table is then at ftp-ftable, and other data such as length, phase masks, cps-to-incr converters, are also accessed from this pointer. See the FUNC structure in cs.h, the ftfind() code in fgens.c, and the code for oscset() and koscil() in opcodes2.c.

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