SCSI Device Command  Operation
-------------------  ---------
HD_SCSICMD           Issue a SCSI-direct command to a SCSI unit.


Trackdisk Device Commands Supported by the SCSI Device
------------------------------------------------------
TD_CHANGESTATE       Return the disk present/not-present status of a drive.
TD_FORMAT            Initialize one or more tracks with a data buffer.
TD_PROTSTATUS        Return the write-protect status of a disk.
TD_SEEK              Move the head to a specific track.


Exec Commands Supported by SCSI Device
--------------------------------------
CMD_READ             Read one or more sectors from a disk.
CMD_START            Restart a SCSI unit that was previously stopped with
                     CMD_STOP.
CMD_STOP             Stop a SCSI unit.
CMD_WRITE            Write one or more sectors to a disk.


Exec Functions as Used in This Chapter
--------------------------------------
AbortIO()            Abort an I/O request to the SCSI device.
AllocMem()           Allocate a block of memory.
AllocSignal()        Allocate a signal bit.
CheckIO()            Return the status of an I/O request.
CloseDevice()        Relinquish use of the SCSI device. All requests must
                     be complete before closing.

DoIO()               Initiate a command and wait for completion
                     (synchronous request).

FreeMem()            Free a block of previously allocated memory.
FreeSignal()         Free a previously allocated signal.
OpenDevice()         Obtain use of the SCSI device.  You specify the type
                     of unit and its characteristics in the call to
                     OpenDevice().

WaitIO()             Wait for completion of an I/O request and remove it
                     from the reply port.


Exec Support Functions as Used in This Chapter
----------------------------------------------
CreateExtIO()        Create an extended IORequest structure for use in
                     communicating with the SCSI device.

CreatePort()         Create a message port for reply messages from the
                     SCSI device.  Exec will signal a task when a message
                     arrives at the port.

DeleteExtIO()        Delete the extended IORequest structure created by
                     CreateExtIO().

DeletePort()         Delete the message port created by CreatePort().