Explanation of read program

For an example, here is read program.

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdio.h>
#include "ppci.h"

// This method prints contents of all registers
// in P-PCI-LV.
void dump_reg(struct ppci *ppci, int minor ) {

  printf("Output data   = %x\n", ppci->data);
  printf("LED = %x\n", ppci->led);
  printf("Switch Register   = %x\n", ppci->sw);
  printf("Transfer Address   = %x\n", ppci->address);
  printf("Transfer Count = %x\n", ppci->length);
  printf("Mode   = %x\n", ppci->mode);
  printf("Status   = %x\n", ppci->status);
  printf("RetLength = %x\n", ppci->retlen);
  printf("FIFOLength = %x\n", ppci->fifolen);
}

// This is a main program.
main(int argc, char **argv) {
  int fd;
  unsigned int i, j, k;
  int minor, direction, control=0;
  int length, retlen;
  int *w_buffer, *r_buffer;
  struct ppci ppci;
  int loop, count;

  if( argc != 4 ) {
    printf("usage : read minor_number loop count\n");
    exit(0);
  }
  minor = atoi(argv[1]);
  loop = atoi(argv[2]);
  count = atoi(argv[3]);

// The minor number is used as the identification of
// P-PCI-LV.
  if( minor == 0 )
    fd = open("/dev/ppci0", O_RDWR);
  else if( minor == 1 )
    fd = open("/dev/ppci1", O_RDWR);
  else {
    printf("Illegal minor number! 0 or 1\n");
    exit(0);
  }

// Allocate buffers for read and predefined data.
  r_buffer = (int *)malloc(count*sizeof(int));
  w_buffer = (int *)malloc(count*sizeof(int));

// Fill predefined data.
// The bit patter in data is good for checking
// crosstalk on a cable.
  for(i = 0; i< count; i++) {
    if((i%2) == 0 )
      w_buffer[i] = 0xaaaaaaaa;
    if((i%2) == 1 )
      w_buffer[i] =  0x55555555;
    r_buffer[i] = 0;
  }

// The direction means "read". 
// The function should be called first for determining
// the direction of data transfer.
  direction = 0;
  if( ioctl(fd, PPCIIOC_RESET, direction) == -1 ) {
    printf("ioctl PPCIIOC_RESET error...\n");
    exit(0);
  }

// Read contents of all regsiters in P-PCI-LV and the
// prints it out.
  if( ioctl(fd, PPCIIOC_DUMP_REGISTERS, &ppci) == -1 ) {
    printf("ioctl PPCIIOC_GET_CONTROL error...\n");
    exit(0);
  }
  dump_reg(&ppci, minor);

  length = count*sizeof(int);
  for(k = 0; k < loop; k++) {
// Read data. retlen will contains actual length transferred.
// if error occurrs, exit with error message.
// The error may "timeout". 
// The value of timeout is 5 sec. as default.
    retlen = read(fd, r_buffer, length);
    if( retlen < 0 || retlen > length) {
      printf("read error occurred...\n");
      exit(0);
    }
// Compare read data with predefined data(writen data).
// If data error detects, exit with error message.
// Otherwise, continue.
    for(i = 0; i < count; i++) {
      if( w_buffer[i] != r_buffer[i] ) {
        printf("data error : loop = %d, i = %d\n", loop, i);
        printf("written data read data\n");
        for(j = i; j < 10; j++)
               printf("%x    %x\n", w_buffer[j], r_buffer[j]);
        free(r_buffer);
        free(w_buffer);
        close(fd);
        exit(0);
      }
      r_buffer[i] = 0;
    }
    if(!(k % 10000))
      printf("loop = %d\n", k);
  }
// If all data transfers finish, close the device.
  close(fd);
}