#define  WORK_BUF_SIZE   64

/**************************************************************************/
/* CHARS_PER_SEC                                                          */
/* FIXED_TIMEOUT_TIME                                                     */  
/* Controls time out time in both transmitting and receiving messages     */
/*                                                                        */
/* Very precise time out control is allowed by setting these values.      */
/* FIXED_TIMEOUT_TIME is also used as the time out time for receiving the */
/* lead character and the length of a message when time out is enabled    */
/* for receiving a message. After the length of the message is received,  */
/* a new time out time (used for receiving the rest of the message) is    */
/* computed based on CHARS_PER_SEC.                                       */
/*                                                                        */
/* Conservative estimates for CHARS_PER_SEC for different baud rates:     */
/*     1200 baud  100                                                     */
/*     9600 baud  800                                                     */
/**************************************************************************/
#define  CHARS_PER_SEC         800 
#define  FIXED_TIMEOUT_TIME    1000

/* Special station values are 0x6000 - 0x603f. */
#define ANY_STAT      0x603f   
#define NO_STAT       0x603e
#define DEST_STAT     20
#define HAND_MAX      4

#define O_RAW   O_BINARY    /* This macro translates the C 2.0 name      */
                            /* used to force binary mode for files.      */

/* Message types : */
#define ACK      1
#define NAK      2
#define GETD     10        /* Get discrete values.                        */
#define GETB     11        /* Get bytes of discrete values.               */
#define GETA     12        /* Get analog values.                          */
#define PUTB     15        /* Put bytes of discrete values.               */
#define PUTA     16        /* Send analog values.                         */
#define SETD     17        /* Turn on all discrete values specified.      */
#define CLRD     18        /* Turn off all discrete values specified.     */

/* I/O Types:  */
#define DEF_IN            0
#define DEF_OUT           1
#define FLT_IN           22
#define FLT_OUT          23

/* Special value for time out computations in Microsoft C. */
#define TICKS_PER_SEC (18.2)

#define   IS_SPECIAL     0x0001
#define   LEAD_CHAR      0x0002

#define   GET_LEAD_CHAR  0x0001
#define   GET_SPECIAL    0x0002

typedef unsigned char  uchar;
typedef signed char    schar;
typedef unsigned short ushort;
typedef unsigned long  ulong;
typedef volatile short aio_t;

typedef
  struct {
    short  stat;       /* Station number being talked to.                */
    schar  m_in;       /* Ptr to next free byte in m_buf.                */
    schar  m_out;      /* Ptr to 1st byte to send in m_buf.              */
    schar  m_cnt;      /* Number of bytes in m_buf. (128 max)            */
    schar  s_in;       /* Ptr to next free byte in s_buf.                */
    schar  s_out;      /* Ptr to 1st byte to send in s_buf.              */
    schar  s_cnt;      /* Number of bytes in s_buf. (128 max)            */
    uchar  s_buf[128]; /* Buffer for characters going to slave port      */
    uchar  m_buf[128]; /* Buffer for characters going to master port.    */
  } PT_CONT;

/* Control block for Universal Driver has all neccessary information.    */
/*   - control block is to be declared as a local variable.              */
/*   - control block is passed to all Universal Driver functions.        */
/*   - no global variables exist for the Universal Driver.               */
/* With all of these conditions met, the Universal Driver is reentrant   */
/* which means that multiple copies of any of its' functions or tasks    */
/* can be executed concurrently.                                         */

typedef
  struct {
    uchar  wbuf[WORK_BUF_SIZE];  /* Commands are written here and        */
                                 /* responses are received here.         */
    int    buf_i;    /* Index into wbuf.                                 */
    int    num_read; /* Number of chars read, used by 'rv' only.         */
    short  form;     /* Format BIN or HEX.                               */
    short  len;      /* Total message length (not including len byte).   */
    short  hlen;     /* Length of header info.                           */
    short  dlen;     /* Length of data.                                  */
    short  stat;     /* Receiving station number.                        */
    short  orig;     /* Sending stations station number.                 */
    short  sess;     /* Session number.                                  */
    short  cmd;      /* Type of command.                                 */
    short  timo;     /* Time out enable.                                 */
    ushort to_time;  /* Time out time, used if timo is enabled. This is  */
                     /* computed by: CHARS_PER_SEC / FIXED_TIMEOUT_TIME  */
    ushort s_time;   /* Start time.                                      */
    short  start;    /* This is used in time control.                    */
    ushort crc;      /* Working value of crc.                            */
    uchar  id;       /* Byte sequence number is echoed by this driver.   */
  } MSG_CONT;

typedef
  struct {
    int        control;   /* Control word to flag various info:  */
    MSG_CONT        tx;   /* Transmit message control structure. */
    MSG_CONT        rv;   /* Receive  message control structure. */
  } UD_CONT;

/* Lowest Level Functions */
int   udgetchar( UD_CONT  *ct, ushort   *inchar);
int   get_mess_char(UD_CONT *ct,ushort *inchar, ushort control );
short set_transmit_timo(UD_CONT *ct, ushort mess_len);
short write_cmd_buf(UD_CONT *ct, ushort outval, ushort control );
short flush_cmd_buf(UD_CONT *ct);
int  num_bytes_avail(UD_CONT *ct);
int  free_buf_space(UD_CONT *ct);

/* Middle Level Functions */
int   transmit_mess(UD_CONT *ct,uchar *hbuff, uchar *dbuff);
int   receive_mess(UD_CONT *ct,uchar *buff);
int   init_udr_ct(UD_CONT *ct);