linux/include/linux/pg.h
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   1/*      pg.h (c) 1998  Grant R. Guenther <grant@torque.net>
   2                       Under the terms of the GNU General Public License
   3
   4
   5        pg.h defines the user interface to the generic ATAPI packet
   6        command driver for parallel port ATAPI devices (pg). The
   7        driver is loosely modelled after the generic SCSI driver, sg,
   8        although the actual interface is different.
   9
  10        The pg driver provides a simple character device interface for
  11        sending ATAPI commands to a device.  With the exception of the
  12        ATAPI reset operation, all operations are performed by a pair
  13        of read and write operations to the appropriate /dev/pgN device.
  14        A write operation delivers a command and any outbound data in
  15        a single buffer.  Normally, the write will succeed unless the
  16        device is offline or malfunctioning, or there is already another
  17        command pending.  If the write succeeds, it should be followed
  18        immediately by a read operation, to obtain any returned data and
  19        status information.  A read will fail if there is no operation
  20        in progress.
  21
  22        As a special case, the device can be reset with a write operation,
  23        and in this case, no following read is expected, or permitted.
  24
  25        There are no ioctl() operations.  Any single operation
  26        may transfer at most PG_MAX_DATA bytes.  Note that the driver must
  27        copy the data through an internal buffer.  In keeping with all
  28        current ATAPI devices, command packets are assumed to be exactly
  29        12 bytes in length.
  30
  31        To permit future changes to this interface, the headers in the
  32        read and write buffers contain a single character "magic" flag.
  33        Currently this flag must be the character "P".
  34
  35*/
  36
  37#define PG_MAGIC        'P'
  38#define PG_RESET        'Z'
  39#define PG_COMMAND      'C'
  40
  41#define PG_MAX_DATA     32768
  42
  43struct pg_write_hdr {
  44
  45        char    magic;          /* == PG_MAGIC */
  46        char    func;           /* PG_RESET or PG_COMMAND */
  47        int     dlen;           /* number of bytes expected to transfer */
  48        int     timeout;        /* number of seconds before timeout */
  49        char    packet[12];     /* packet command */
  50
  51};
  52
  53struct pg_read_hdr {
  54
  55        char    magic;          /* == PG_MAGIC */
  56        char    scsi;           /* "scsi" status == sense key */
  57        int     dlen;           /* size of device transfer request */
  58        int     duration;       /* time in seconds command took */
  59        char    pad[12];        /* not used */
  60
  61};
  62
  63/* end of pg.h */
  64
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