Technotes

Technote DV 02

March 1987

Changes since March 1, 1988: Updated the _DrvrInstall text to reflect the use of register A0, which should contain a pointer to the driver when called. Also added simple glue code for _DrvrInstall and _DrvrRemove since none is available in the MPW interfaces.

_AddDrive

_AddDrive adds a drive to the drive queue, and is discussed in more detail in Technical Note #36, Drive Queue Elements:

        FUNCTION AddDrive(DQE:DrvQE1;driveNum,refNum:INTEGER):OSErr;

                A0 (input)              ->     pointer to DQE
               D0 high word(input)       ->     drive number
               D0 low word(input)        ->     driver RefNum
               D0 (output)             <-      error code
                                     noErr (always returned)

_DrvrInstall

_DrvrInstall is used to install a driver. A DCE for the driver is created and its handle entered into the specified Unit Table position (-1 through -64). If the unit number is -4 through -9, the corresponding ROM-based driver will be replaced:

        FUNCTION DrvrInstall(drvrHandle:Handle; refNum: INTEGER): OSErr;

               A0 (input)        ->    pointer to driver
               D0 (input)        ->    driver RefNum (-1 through -64)
               D0 (output)       <-    error code
                                     noErr
                                     badUnitErr

_DrvrRemove

_DrvrRemove is used to remove a driver. A RAM-based driver is purged from the system heap (using _ReleaseResource). Memory for the DCE is disposed:

        FUNCTION DrvrRemove(refNum: INTEGER):OSErr;

               D0 (input)        ->    Driver RefNum
               D0 (output)       <-    error code 
                                    noErr
                                    qErr

Interfaces

Through a sequence of cataclysmic events, the glue code for _DrvrInstall and _DrvrRemove was never actually added to the MPW interfaces (i.e., "We forgot."), so we will include simple glue here at no extra expense to you.

It would be advisable to first lock the handle to your driver with _HLock before making either of these calls since memory may be moved.

       ;---------------------------------------------------------------
       ; FUNCTION DRVRInstall(drvrHandle:Handle; refNum:INTEGER):OSErr;
       ;---------------------------------------------------------------

       DRVRInstall      PROC    EXPORT
              MOVEA.L           (SP)+, A1    ; pop return address
              MOVE.W	          (SP)+, D0    ; driver reference number
              MOVEA.L           (SP)+, A0    ; handle to driver 
              MOVEA.L           (A0), A0     ; pointer to driver
              _DrvrInstall                   ; $A03D
              MOVE.W            D0, (SP)     ; get error
              JMP               (A1)         ; & split
              ENDPPROC


       ;---------------------------------------------------------------
       ; FUNCTION DRVRRemove(refNum:INTEGER):OSErr;
       ;---------------------------------------------------------------

       DRVRRemove      PROC    EXPORT
              MOVEA.L          (SP)+, A1    ; pop return address
              MOVE.W           (SP)+, D0    ; driver reference number
              _DrvrRemove                   ; $A03E
              MOVE.W           D0, (SP)     ; get error
              JMP              (A1)         ; & split
              ENDPPROC