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     ch — SCSI media-changer (juke box) driver


     device ch


     The ch driver provides support for a SCSI media changer.  It allows many slots of media to
     be multiplexed between a number of drives.  The changer device may optionally be equipped
     with a bar code reader, which reads label information attached to the media.

     A SCSI adapter must also be separately configured into the system before a SCSI changer can
     be configured.

     As the SCSI adapter is probed during boot, the SCSI bus is scanned for devices.  Any devices
     found which answer as 'Changer' type devices will be 'attached' to the ch driver.  In
     FreeBSD releases prior to 2.1, the first found will be attached as ch0 and the next, ch1
     etc.  Beginning in 2.1 it is possible to specify what ch unit a device should come on line
     as; refer to scsi(4) for details on kernel configuration.


     It is only necessary to explicitly configure one ch device; data structures are dynamically
     allocated as media changes are found on the SCSI bus.


     User mode programs communicate with the changer driver through a number of ioctls which are
     described below.  Changer element addresses used in the communication between the kernel and
     the changer device are mapped to zero-based logical addresses.  Element types are specified
     as follows:

     CHET_MT  Medium transport element (picker).

     CHET_ST  Storage element (slot).

     CHET_IE  Import/export element (portal).

     CHET_DT  Data transfer element (drive).

     The following ioctl(2) calls apply to the changer.  They are defined in the header file

     CHIOMOVE      (struct changer_move) Move a medium from one element to another (MOVE MEDIUM)
                   using the current picker.  The source and destination elements are specified
                   in a changer_move structure, which includes at least the following fields:

                         u_int cm_fromtype; /* element type to move from */
                         u_int cm_fromunit; /* logical unit of from element */
                         u_int cm_totype;   /* element type to move to */
                         u_int cm_tounit;   /* logical unit of to element */
                         u_int cm_flags;    /* misc. flags */
                   If the CM_INVERT in the cm_flags field is set, the medium changer is
                   instructed to flip the medium while moving it.

     CHIOEXCHANGE  (struct changer_exchange) Move the medium located in the source element to the
                   first destination element, and move the medium that had been in the first
                   destination element to the second destination element.  In case of a simple
                   exchange, the source and second destination elements should be the same.  The
                   current picker is used to perform the operation.  The addresses of the
                   affected elements is specified to the ioctl in a changer_exchange structure
                   which includes at least the following fields:

                         u_int ce_srctype;        /* element type of source */
                         u_int ce_srcunit;        /* logical unit of source */
                         u_int ce_fdsttype; /* element type of first destination */
                         u_int ce_fdstunit; /* logical unit of first destination */
                         u_int ce_sdsttype; /* element type of second destination */
                         u_int ce_sdstunit; /* logical unit of second destination */
                         u_int ce_flags;  /* misc. flags */
                   In ce_flags, CM_INVERT1 and/or CM_INVERT2 may be set to flip the first or
                   second medium during the exchange operation, respectively.

                   This operation is untested.

     CHIOPOSITION  (struct changer_position) Position the current picker in front of the
                   specified element.  The element is specified with a changer_position
                   structure, which includes at least the following elements:

                         u_int cp_type;  /* element type */
                         u_int cp_unit;  /* logical unit of element */
                         u_int cp_flags; /* misc. flags */
                   The cp_flags field may be set to CP_INVERT to invert the picker during the

     CHIOGPICKER   (int) Return the logical address of the current picker.

     CHIOSPICKER   (int) Select the picker specified by the given logical address.

     CHIOGPARAMS   (struct changer_params) Return the configuration parameters for the media
                   changer.  This ioctl fills the changer_params structure passed by the user
                   with at least the following fields:

                         u_int cp_npickers; /* number of pickers */
                         u_int cp_nslots;   /* number of slots */
                         u_int cp_nportals; /* number of import/export portals */
                         u_int cp_ndrives;  /* number of drives */

                   This call can be used by applications to query the dimensions of the jukebox
                   before using the CHIGSTATUS ioctl to query the jukebox status.

     CHIOIELEM     Perform the INITIALIZE ELEMENT STATUS call on the media changer device.  This
                   forces the media changer to update its internal status information with
                   respect to loaded media.  It also scans any barcode labels provided that it
                   has a label reader.  The ch driver's status is not affected by this call.

     CHIOGSTATUS   (struct changer_element_status_request) Perform the READ ELEMENT STATUS call
                   on the media changer device.  This call reads the element status information
                   of the media changer and converts it to an array of changer_element_status

                   With each call to CHIOGSTATUS, the status of one or more elements of one type
                   may be queried.

                   The application passes a changer_element_status_request structure to the ch
                   driver which contains the following fields:

                         u_int                          cesr_element_type;
                         u_int                          cesr_element_base;
                         u_int                          cesr_element_count;
                         u_int                          cesr_flags;
                         struct changer_element_status *cesr_element_status;

                   This structure is read by the driver to determine the type, logical base
                   address and number of elements for which information is to be returned in the
                   array of changer_element_status structures pointed to by the
                   cesr_element_status field.  The application must allocate enough memory for
                   cesr_element_count status structures (see below).  The cesr_flags can
                   optionally be set to CESR_VOLTAGS to indicate that volume tag (bar code)
                   information is to be read from the jukebox and returned.

                   The cesr_element_base and cesr_element_count fields must be valid with respect
                   to the physical configuration of the changer.  If they are not, the
                   CHIOGSTATUS ioctl returns the EINVAL error code.

                   The information about the elements is returned in an array of
                   changer_element_status structures.  This structure include at least the
                   following fields:

                         u_int            ces_addr;      /* element address in media changer */
                         u_char           ces_flags;     /* see CESTATUS definitions below */
                         u_char           ces_sensecode; /* additional sense code for element */
                         u_char           ces_sensequal; /* additional sense code qualifier */
                         u_char           ces_invert;    /* invert bit */
                         u_char           ces_svalid;    /* source address (ces_source) valid */
                         u_short          ces_source;    /* source address of medium */
                         changer_voltag_t ces_pvoltag;   /* primary volume tag */
                         changer_voltag_t ces_avoltag;   /* alternate volume tag */
                         u_char           ces_idvalid;   /* ces_scsi_id is valid */
                         u_char           ces_scsi_id;   /* SCSI id of element (if ces_idvalid is nonzero) */
                         u_char           ces_lunvalid;  /* ces_scsi_lun is valid */
                         u_char           ces_scsi_lun;  /* SCSI lun of element (if ces_lunvalid is nonzero) */

                   The ces_addr field contains the address of the element in the coordinate
                   system of the media changer.  It is not used by the driver, and should be used
                   for diagnostic purposes only.

                   The following flags are defined for the ces_flags field:

                   CESTATUS_FULL    A medium is present.

                   CESTATUS_IMPEXP  The medium has been deposited by the operator (and not by a

                   CESTATUS_EXCEPT  The element is in an exceptional state (e.g. invalid barcode
                                    label, barcode not yet scanned).

                   CESTATUS_ACCESS  The element is accessible by the picker.

                   CESTATUS_EXENAB  The element supports medium export.

                   CESTATUS_INENAB  The element supports medium import.

                   Note that not all flags are valid for all element types.


     This version of the ch driver has been tested with a DEC TZ875 (5 slot, one DLT drive) and a
     Breece Hill Q47 (60 slot, four DLT drives, barcode reader).

     Many of the features the ch driver supports are not thoroughly tested due to the fact that
     the devices available for testing do not support the necessary commands.  This is true for
     alternate volume tags, media flipping, import/export element handling, multiple picker
     operation and other things.


     /dev/ch[0-9]  device entries


     If the media changer does not support features requested by the ch driver, it will produce
     both console error messages and failure return codes to the ioctls described here.


     chio(1), cam(4), cd(4), da(4), sa(4)


     The ch driver appeared in 386BSD 0.1.


     The ch driver was written by Jason R. Thorpe <> for And Communications,  It was added to the system by Stefan Grefen
     <> who apparently had such a device.  It was ported to CAM by
     Kenneth Merry <>.  It was updated to support volume tags by Hans Huebner