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+====== HD-Park-Switch ======
+(or How to Patch a CMD-HD to your own needs)
+  * By Ninja/The Dreams
+  * Originally published in Domination #17
+  * Converted to ascii by Jazzcat/Onslaught
+One thing I really like about the C64 nowadays is that it is a quiet computer.
+No fans or similar, just wonderful! Unfortunately, the SCSI-HDD inside my
+CMD-HD is the opposite. When it is running, it sounds like an aeroplane.
+Being a curious programmer, I tried to get rid of this annoyance. I realised that I never use the 'Write protect' button. So, maybe I could abuse it to park/unpark my HDD?
+Well, the forthcoming project might not be too useful for most of you.
+Nevertheless, it might give you an idea how the CMD-HD works and how to apply own patches to the CMD-HD-ROM. You never know when you might need that!
+====== How to do ======
+First of all, the HD-ROM is not really ROM but in fact RAM which can be protected from storing data to it.
+This makes sense, as the HD-KERNAL has to be loaded from the system partition when the HD boots up.
+Furthermore, upgrading the HD-DOS does not require hardware modifications. Ofcourse, it also means that applying patches is pretty easy: unprotect RAM, modify KERNAL, protect RAM. If the 1541 had such capabilities...
+The patch itself is quite simple.
+Install a backpack to that point where the 'Write protect'-flag was toggled.
+From there, send the corresponding SCSI-jobcode to park/unpark the HD-mechanism. Finally go back to the standard procedure.
+ROM-versions 1.86, 1.90 and 1.92 are handled (are there any more though?), though only 1.92 was tested. As we do just easy stuff, I do not expect many problems with those older versions. For the rest, I will let the source-code speak (I assume you know a little about sending and executing drive code.
+All necessary information was re-engineered (and that was the main work) by me or Doc Bacardi/The Dreams
+Enjoy and comments are welcome.
+====== The code ======
+<code>
+; HD-Park-Switch V1.0 by Ninja/The Dreams in 2002
+org $0801
+binclude "help/hdpshead.prg",2
+; include BASIC-header, which contains
+; some information and will start the
+; following routines.
+; Works in 64 and 128-mode!
+align 256    ; start at beginning of a page
+jmp in:
+lda #$0f     ; channel #15
+ldx $ba       ; use current device
+tay              ; use command channel
+jsr $ffba    ; set file-parameters
+lda $fff6
+cmp #$ff    ; check platform
+bne c64_found    ; c64, then jump
+lda #$0f
+tax              ; set memconfig for channel
+jsr $ff68    ; in C128-mode
+ldy $2e        ; get C128-BASIC-start
+byt $2c       ; skip next opcode
+c64_found:
+ldy $2c       ; get C64-BASIC-start
+iny              ; increment to point to this
+                   ; page
+ldx #lo (mw-command)  ; lobyte of
+                                        ; command
+lda #hd_code_len+6   ; we send all
+                                       ; bytes at once
+jsr $ffbd   ; set up memory-write-
+                   ; command
+jsr $ffc0   ; send command
+ldx #$0f
+jsr $ffc6   ; set channel as input
+jsr $ffcf    ; get char
+cmp #'0'    ; "0" from OK-string?
+bne drive_err   ; if not, skip execution
+                          ; will probably be a non
+                          ; CMD-HD-drive
+                          ; complaining about the
+                          ; long command string
+ldx #$0f
+jsr $ffc9        ; channel as output
+lda #'U'
+jsr $ffd2
+lda #'3'
+jsr $ffd2        ; send "U3", executes at
+                        ; $0500
+drive]err:
+jsr $ffcc        ; restore input/output
+lda #$0f
+jmp $ffc3       ; close channel and go
+                        ; back
+mw]command:
+byt "M-W",0,5,hd_code_len
+hd]code:
+phase $0500   ; HD-code is at $0500
+sei                   ; no interrupts
+ldy #2             ; check 3 ROM versions
+                        ; (1.86, 1.90, 1.92)
+next_rom:
+ldx rom_ofs,y  ; get version-specific
+                          ; offset into x
+lda #$4c           ; $4c = JMP opcode
+cmp $f28a,x     ; present in ROM?
+bne wrong_rom  ; no, then next version
+sta bp_mod+1    ; store address]lo into
+                            ; our backpack
+lda rom_jmplo,y  ; get version-specific
+                              ; offset into x
+lda #$4c               ; $4c = JMP opcode
+cmp $f28b,x         ; present in ROM?
+bne wrong_rom   ; no, then next version
+sta bp_mod+1    ; store address]lo into
+                            ; our backpack
+lda_rom_jmphi,y  ; get version-specific
+                               ; address]hi
+cmp $f28c,x           ; present in ROM?
+beq rom_found      ; yes, then go patch
+wrong_rom:
+dey                      ; try next version
+bpl next_rom     ; still one left?
+cli
+rts                      ; no, then goodbye
+                            ; without changes
+rom_found:
+sta bp]mod+2    ; store address]hi into
+                             ; our backpack
+lda $8f00
+ora #20
+sta $8f00            ; unprotect RAM
+ldy #bp_len-1
+copy_bp:
+lda backpack,y
+sta $ff60,y
+dey
+bpl copy]bp     ; copy backpack to $ff60
+lda #$60
+sta $f28b,x
+lda #$ff            ; apply JMP $ff60 to
+                          ; version-specific
+sta $f28c,x       ; address
+lda $8f00
+and #$df
+sta $8f00          ; protect RAM
+cli
+rts                     ; goodbye
+backpack:
+lda #$f8     ; SCSI_Jobcode 'Start
+                   ; Device'
+bit $49        ; Check for 'Write Protect'
+bpl wp_disabled   ; disabled, then skip
+                               ; next opcode
+lda #$fa  ; SCSI-Jobcode 'Stop Device'
+wp_disabled:
+sta $20  ; into Native-Job-Que
+bp]mod:
+jmp $ffff ; back to original routine self-
+                 ; modified from above
+bp_len     = *-backpack
+;           V1.86            V1.90          V1.92
+roms_ofs:
+byt $f28a-f28a,$f2f6-f28a,$f331-f28a
+; where to patch
+rom_jmplo:
+byt        $be      ,        $2a      ,      $65
+rom_jmphi:
+byt        $f2      ,        $f3       ,      $f3
+; what to patch
+dephase
+hd_code_len   = *-hd_code
+end $0801
+</code>