Retrieving data from ADP/Hydra/Argonaut recorders using the fast binary
transfer (i.e. as used by SONREC).

The protocol is as follows:

1- User sends:    DOWNLOAD  <file name> [CR]

   where <file name> is the name of a file in the recorder as given by the
   DIR command (i.e. DEF001)

2- System responds:  DOWNLOAD <file name> [CR][LF]
                     OK [CR][LF]
                     c

3- User sends:       a

4- System responds:  <file description packet>

5- User sends:       a

6- System responds:  <data packet 1>

7- User sends:       a

8- System responds:  <data packet 2>
                   .    .    .
                   .    .    .
                   .    .    .
                   .    .    .
                   .    .    .
N- System responds:  <data packet last>

N+1- System responds:  [CR][LF] OK [CR][LF]



A data packet consists of:

unsigned int Nytes -   2-byte integer with the number of bytes in the packet
                   including these 2 and the 2 for the checksum

char         Buf[Nbytes-4]  -  Nbytes-4 consecutive bytes of data

             Checksum - unsigned 2-byte integer with the checksum of the
                        Nbytes-4 bytes in Buf only. This checksum is computed
                        with the function "ComputeCheckSum" shown below.

In the file description packet the buf sent is simply a file description
data structure as defined below.

All other data packets are normally 1024 bytes long, except for the last data
packet which may be smaller. Each data packet after the file description packet
is simply an exact image of the data in the file being downloaded.

The user should verify the integrity of each packet by comparing the checksum
in the packet to the checksum computed from the packet data itself. If they
don't match, the user can request the same packet to be resent by simply sending
the character "r" to the system, instead of the "a", as many times as needed.



/*=========================================================================*/
/*                                                                         */
/*   Definition of DateTime structure used by other ADP data structures    */
/*                                                                         */
/*                                                                         */
typedef struct
{
   int  year;
   char day,
        month,
        minute,
        hour,
        sec100,
        second;
} DateTimeType;
/*                                                                         */
/*                                                                         */
/*=========================================================================*/
/*=========================================================================*/
/*                                                                         */
/*   Definition of file description structure used by the ADP recorder     */
/*                                                                         */
/*                                                                         */
typedef struct _RecFileDescType
{
  char           FileName[13];    /* Same as given by DIR command          */
                                  /* i.e. DEF001                           */
  long           FileSize;        /* In bytes                              */
  int            FileIndex;       /* File sequence number within recorder  */
  char           Attrib;          /* 0-normal file;                        */
                                  /* 1-overwritten in buffer mode          */
  DateTimeType   DateTime;        /* Date/time file was created in recorder*/

} RecFileDescType;
/*                                                                         */
/*                                                                         */
/*-------------------------------------------------------------------------*/
/*===========================================================================*/
/*                                                                           */
/*   Check sum computation in for recorder transfer                          */
/*                                                                           */
#define CHECK_SUM_OFFSET   0xA596
unsigned int ComputeCheckSum( unsigned char *buf, int n )
{
  int i;
  unsigned int ChkSum = CHECK_SUM_OFFSET;
  for(i=0;i<n;i++) ChkSum += buf[i];
  return(ChkSum);
}
/*                                                                           */
/*                                                                           */
/*---------------------------------------------------------------------------*/