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https://frontier.innolan.net/github/AmigaExamples.git
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204 lines
3.9 KiB
ArmAsm
204 lines
3.9 KiB
ArmAsm
*** MFMLoader.S by Photon *** ;requires a6=$dff002
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xdef LoadMFMB
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MFMsync equ $4489 ;AmigaDOS standard sync marker.
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MFMlen equ 12980 ;Legacy trackdata read length in bytes
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ShortWt:MACRO ;CPU-independent nop;nop replacement
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tst.w (a6)
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ENDM
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MFMcyl: dc.w 0
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MFMhead: dc.w 0
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MFMdrv: dc.w 0
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MFMchk: dc.l 0
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LoadMFMB: ;loadsectors.a0=dst,d0=startsec.W,d1=nrsecs.W(-=Step0)
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MOVEM.L D0-D7/A0-A6,-(SP)
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lea $bfd100,a4
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bsr MotorOn
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tst.w d1 ;if neg length,then Step0 first
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bpl.s .NoSt0
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neg.w d1
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.St0: btst #4,$f01(a4) ;head on cyl 0?
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beq.s .Rdy0
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bsr.s StepOut
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bra.s .St0
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.Rdy0: lea MFMcyl(PC),a1
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clr.w (a1)
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.NoSt0: and.l #$ffff,d0
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divu #22,d0 ;startcyl
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sub.w MFMcyl(PC),d0 ;delta-step
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beq.s .StRdy
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bmi.s .StOut
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subq.w #1,d0
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.StIn: bsr.s StepIn
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dbf d0,.StIn
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bra.s .StRdy
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not.w d0 ;=neg+sub#1
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.StOut: bsr.s StepOut
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dbf d0,.StIn
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.StRdy: swap d0 ;startsec within cyl
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cmp.w #11,d0
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blt.s .Head0
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sub.w #11,d0
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bra.s .Head1
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.Head0: bset #2,(a4)
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lea MFMhead(PC),a1
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clr.w (a1)
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bsr LoadTrak ;read track+decode
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beq.s .End
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.Head1: bclr #2,(a4) ;Head 1
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lea MFMhead(PC),a1
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move.w #1,(a1)
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bsr LoadTrak ;read track+decode
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beq.s .End
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bsr.s StepIn ;1 cyl forward
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bra.s .Head0
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.End: bsr.s MotorOff
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MOVEM.L (SP)+,D0-D7/A0-A6
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RTS
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StepOut:
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bset #1,(a4)
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lea MFMcyl(PC),a1
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subq.w #1,(a1)
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ShortWt
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bclr #0,(a4)
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ShortWt
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bset #0,(a4)
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bsr.s StepWt
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RTS
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StepIn:
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bclr #1,(a4)
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lea MFMcyl(PC),a1
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addq.w #1,(a1)
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ShortWt
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bclr #0,(a4)
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ShortWt
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bset #0,(a4)
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bsr.s StepWt
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RTS
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StepWt:
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moveq #67,d6 ;wait >3 ms
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LeaveLine:
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.loop1: move.b 6-2(a6),d7
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.loop2: cmp.b 6-2(a6),d7
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beq.s .loop2
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dbf d6,.loop1
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RTS
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MotorOn:
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move.w MFMdrv(PC),d7
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addq.w #3,d7
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or.b #$78,(a4)
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bset d7,(a4)
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ShortWt
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bclr #7,(a4) ;turns motor on
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ShortWt
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bclr d7,(a4)
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ShortWt
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.DiskR: btst #5,$f01(a4) ;wait until motor running
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bne.s .DiskR
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RTS
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MotorOff:
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move.w MFMdrv(PC),d7
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addq.w #3,d7
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bset d7,(a4)
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ShortWt
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bset #7,(a4)
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ShortWt
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bclr d7,(a4)
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RTS
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LoadTrak: ;loadtrack+decode.a0=dst,d0=secoffs,d1=secsleft
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MOVE.W D0,-(SP)
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MOVE.W D1,-(SP)
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lea MFMbuf,a1
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move.w #2,$9c-2(a6) ;Clr Req
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move.l a1,$20-2(a6)
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move.w #$8210,$96-2(a6) ;DskEna
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move.w #MFMsync,$7e-2(a6)
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move.w #$9500,$9e-2(a6)
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move.w #$4000,$24-2(a6)
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move.w #$8000+MFMlen/2,$24-2(a6);DskLen(12980)+DmaEn
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move.w #$8000+MFMlen/2,$24-2(a6);start reading MFMdata
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.Wrdy:
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btst #1,$1f-2(a6) ;wait until data read
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beq.s .Wrdy
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move.w d0,d2
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add.w d1,d2 ;highest sec# (d0=lowest)
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cmp.w #11,d2
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ble.s .NoOvr
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moveq #11,d2
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.NoOvr: sub.w d0,d2 ;nrsecs
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move.l #$55555555,d3 ;and-const
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move.w d2,d1
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subq.w #1,d1 ;loopctr
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.FindS: cmp.w #MFMsync,(a1)+ ;search for a sync word
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bne.s .FindS
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cmp.b (a1),d3 ;search for 0-nibble
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bne.s .FindS
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move.l (a1)+,d4 ;decode fmtbyte/trk#,sec#,eow#
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move.l (a1)+,d5
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and.w d3,d4
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and.w d3,d5
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add.w d4,d4
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or.w d5,d4
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lsr.w #8,d4 ;sec#
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sub.w d0,d4 ;do we want this sec?
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bmi.s .Skip
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cmp.w d2,d4
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blt.s .DeCode
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.Skip: lea 48+1024(a1),a1 ;nope
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bra.s .FindS
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.DeCode:lea 40(a1),a1 ;found a sec,skip unnecessary data
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move.l a1,d6
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lea MFMchk(PC),a1
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clr.l (a1)
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move.l d6,a1
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move.l (a1)+,d6 ;decode data chksum.L
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move.l (a1)+,d5
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and.l d3,d6
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and.l d3,d5
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add.l d6,d6
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or.l d5,d6 ;chksum
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lea 512(a1),a2
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add.w d4,d4 ;x512
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lsl.w #8,d4
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lea (a0,d4.w),a3 ;dest addr for this sec
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moveq #127,d7
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.DClup: move.l (a1)+,d4
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move.l (a2)+,d5
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and.l d3,d4
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and.l d3,d5
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eor.l d4,d6 ;EOR with checksum
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eor.l d5,d6 ;EOR with checksum
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add.l d4,d4
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or.l d5,d4
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move.l d4,(a3)+
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dbf d7,.DClup ;chksum should now be 0 if correct
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lea MFMchk(PC),a1
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or.l d6,(a1) ;or with track total chksum
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move.l a2,a1
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dbf d1,.FindS ;decode next sec
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MOVE.W (SP)+,D1
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MOVE.W (SP)+,D0
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move.l MFMchk(PC),d3 ;track total chksum OK?
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bne LoadTrak ;no,retry
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moveq #0,d0 ;set to start of track
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move.w d2,d3
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add.w d3,d3
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lsl.w #8,d3
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add.w d3,a0
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sub.w d2,d1 ;sub #secs loaded
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RTS
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;MFMbuf is placed here after bootblock end, $3c0.w or so when copied.
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MFMbuf:
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dcb.b MFMlen
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