// C31FILT.C - C31 FILTER PROGRAM
//
// this program allows you to download data from the PC and process
// it on the DSK board. It uses a handshaking approach. It is intended
// to be run using the freader program.
//

// function: filter
//
// arguments:
//  short int* in:	a pointer to the input sample
//  short int* out:	a pointer to the output sample
//  int process:	a flag that controls initialization
//
// return: none
//
// this function processes one sample at a time. the user can
// initialize any internal variables by setting process=0,
// and can process a sample by setting process=1.
//
void filter(short int *in, short int *out, int process) {

  // declare local variables
  //
  float acc = 0;

  // initialization step
  //
  if (process == 0) {
    acc = 0;
  }
  
  // process step
  //
  else if (process == 1) {
    acc = *in;
    *out = acc;
  }
}

// main program
//
// this program serves as a driver for the filter function
// users need not modify this program
//
//
main() {

  // declaration of variables
  //
  int i = 0;
  int init = 0;
  float din = 0.0, dout = 0.0;
  int ready = 1, start = 0, done = 0;
  short int *DSP_READY, *START, *DONE, *OUT, *IN;

  // reserve the memory address locations on the dsp
  // for status flags and registers
  //
  DSP_READY = (short int *)0x809800;	// dsp ready status
  START = (short int *)0x809801;	// dsp start flag
  DONE = (short int *)0x809802;		// dsp done status
  IN = (short int *)0x809803;		// data input address
  OUT = (short int *)0x809804;		// data output address

  // initialize filter variables
  //
  init = 0;
  filter((short int *)NULL, (short int *)NULL, init);

  // initialize dsp status flags and registers
  //
  *START = start;
  *DONE = done;
  *OUT = dout;
  *IN = din;
  *DSP_READY = ready;

  for (;;) {

    // while ready == 1 and start == 0
    //   note that the PC sets start to 1 after reading
    //   a true value for ready
    //
    while (ready == 1) {
      asm("IDLE");
      start = *START;
      if (start == 1) {
	ready = 0;
	*DSP_READY = ready;
      }
    }

    // the PC has set start to 1, which means DSK is ready
    //   to receive the data
    //
    // process the data when it is received
    //
    asm("IDLE");
    init = 1;
    filter((short int *)IN, (short int *)OUT, init);

    // pull start low
    //
    start = 0;
    *START = start;

    // pull done high, signalling the PC to read output
    //
    done = 1;
    *DONE = done;

    // wait for the PC to pull down low
    //
    while (done == 1) {
      done = *DONE;
    }

    // initialize for next iteration
    //
    ready = 1;
    *DSP_READY = ready;
  }
}