/* 
 * bitcounter.c
 *
 * Rotate a wheel with a paper barcode and read off the light values
 *
 * Extending on findsync.c, this version searches for a
 * synchronization bit on the paper. A sync bit is a black mark which
 * extends for SYNC rotation sensor pulses.
 *
 * Once we find the sync bit, count how many bits are read until we
 * hit the SYNC bit again
 *
 * Mark Crosbie  9/10/00  mark@mastincrosbie.com
 */

#define DEBUG
#define BEEP

#include <conio.h>
#include <unistd.h>

#include <sys/dsensor.h>
#include <dmotor.h>
#include <dsound.h>

#define ROTSENSOR SENSOR_1
#define LIGHTSENSOR SENSOR_3

#define MOTOR MOTOR_A

/* some motor speed settings */
#define CRAWL 10
#define SLOW 50
#define MID_SPEED ((MAX_SPEED - MIN_SPEED) / 2)

/* a handy abs() function */
#define ABS(x) ((x)>=0)?(x):-(x)

/* difference in light sensor reading */
#define THRESHOLD 20

/* function prototypes */
void initall(void);
void findSync(void);
int bitLength(void);
void tapeForwards(int speed);
void tapeBackwards(int speed);

int main(int argc, char *argv[]) {

  int length;

  initall();

  /* turn on the tape */
  tapeForwards(SLOW);

  /* find the SYNC bit marker on the tape and stop */
  findSync();

  /* turn the tape on again */
  tapeForwards(SLOW);

  /* and print how long it is */
  length = bitLength(); 
  lcd_int(length);

  return 0;
}

void initall(void) {
  /* initialize the sensors */
  ds_init(); 
  ds_active(&ROTSENSOR);
  ds_active(&LIGHTSENSOR);

  /* start sensor processing */
  ds_rotation_on(&ROTSENSOR);
  ds_rotation_set(&ROTSENSOR, 0);

  /* let sensor reading stabilize */
  msleep(500);
}

void tapeForwards(int speed) {
  /* and turn on the motor */
  motor_a_dir(fwd);
  motor_a_speed(speed);	   
}

void tapeBackwards(int speed) {
  /* and turn on the motor */
  motor_a_dir(rev);
  motor_a_speed(speed);	   
}

/*
 * Name:
 *    findSync
 *
 * Description:
 *    Rotate the tape until the sync bit is located
 *
 * Parameters:
 *    None
 *
 * Returns:
 *    None - returns when sensor is at sync bit
 * 
 * Globals affected:
 *    None
 *
 * Algorithm:
 *    The sync bit on the tape is SYNC rotation counter pulses long.
 *
 */
void findSync(void) {

  int lastlevel = 0;
  int level = 0, diff;

  /* take the initial reading */
  lastlevel = LIGHT_3;

  while(1) {

    level = LIGHT_3;
    diff = ABS(lastlevel - level); 

    /* darker gives a smaller reading from the light sensor.
     * A darker reading indicates the start of a bit. 
     */
    if( diff > THRESHOLD) {
      motor_a_dir(brake);
      msleep(300);
      motor_a_dir(off);
#ifdef BEEP
      dsound_system(DSOUND_BEEP);
#endif
      return;
    }

    lastlevel = level;

    /* for some reason, this msleep is needed to stabilize the reading
     * from the light sensor
     */
    msleep(1);

  }
}

/*
 * Name:
 *    bitLength
 *
 * Description:
 *    Returns the length of the current bit in rotation sensor pulses
 *
 * Parameters:
 *    None
 *
 * Returns:
 *    length
 * 
 * Globals affected:
 *    None
 *
 * Algorithm:
 *    Run the tape until we get a threshold transition and then return
 *    the rotation sensor count
 *
 */
int bitLength(void) {
  
  int lastlevel = 0;
  int level = 0, diff;

  /* take the initial reading */
  lastlevel = LIGHT_3;

  /* reset the rotation sensor */
  ds_rotation_set(&ROTSENSOR, 0);

  while(1) {

    level = LIGHT_3;
    diff = ABS(lastlevel - level); 

    /* darker gives a smaller reading from the light sensor.
     * A darker reading indicates the start of a bit. 
     * Count how long this bit is
     */
    if( diff > THRESHOLD) {
      motor_a_dir(brake);
      msleep(300);
      motor_a_dir(off);
      return ABS(ROTATION_1);
    }

    lastlevel = level;

    /* for some reason, this msleep is needed to stabilize the reading
     * from the light sensor
     */
    msleep(1);
  }
}