* CLI TOY #1
* CLS.ASM:     A command to clear the current (CLI) window. Works by
*              sending a HOME/CLEAR TO END OF SCREEN sequence to CON:
*
* Perpetrator: Dewi Williams  ..!ihnp4!druca!dewi
*              Unconditionally placed in the public domain.

* Included equate files.
* -----------------------------------------------------------------------
      NOLIST 
      INCLUDE  "exec/types.i"
      INCLUDE  "exec/libraries.i"
      INCLUDE  "libraries/dos.i"
      LIST

* Local Equates
* ------------------------------------------------------------------------
SysBase  EQU   4        ; The one known address in the system.

* External references
* -----------------------------------------------------------------------

	EXTERN_LIB	OpenLibrary
	EXTERN_LIB	Write
	EXTERN_LIB	Output
	EXTERN_LIB      IoErr

* macros
* ------------------------------------------------------------------------
* Calls to dos.library and exec library
callsys  MACRO
      CALLLIB      _LVO\1
      ENDM

* The code segment
* -------------------------------------------------------------------------

   RORG     0              ; Relocatable code.

   ;------ get Exec's library base pointer:
   move.l   SysBase,a6
   LEA.L    DOSName(PC),A1    ; name of dos library
   move.l   #LIBRARY_VERSION,d0

   callsys  OpenLibrary
   MOVE.L   D0,A6             ; Save library pointer (always in A6).
   BEQ.S    DOSFAIL           ; Give up!

* Obtaining the output handle (needed for write)
   callsys  Output            ; Always works -- copy from process structure.
   MOVE.L   D0,D1             ; Needed there by write

* Write the sequence to the driver
   LEA.L    CLS(PC),A0
   MOVE.L   A0,D2             ; Effective address of the buffer
   MOVEQ    #4,D3             ; Length of buffer to write
   callsys  Write             ; Do it
   TST.L    D0                ; Just set condition code
   BMI.S    IOFAIL            ; For disks & suchlike check == D3.

* Exit back to CLI (shouldn't close CLI handles).
   MOVEQ    #0,D0             ; Success exit code

FINISHED:
   rts

* All the error traps go here
* ---------------------------

   ; Get here if we can't write to CON: for some reason.
IOFAIL:
   callsys  IoErr          ; Returns real reason for failure.
   BRA.S    FINISHED       ; Quit

   ; Get here if we can't open dos.library. Give up! We should really
   ; alert...
DOSFAIL:
   MOVEQ    #RETURN_FAIL,D0
   RTS

* Data declarations
* ------------------------------------------------
DOSName		DOSNAME;
CLS		DC.B	$9B,'H',$9B,'J'	; HOME, CLEAR TO END OF SCREEN
	END