passport/src/rwts.a

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;-------------------------------
; ReadSector
; high-level function to read a single sector.
; in: gIsProtDOS is TRUE or FALSE
; if gProtDOS is FALSE, callrwts+2 has been set to
; the RWTS entry point (e.g. $BD or $3D)
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; out: all registers clobbered
; C clear if read was successful
; C set if read failed
;-------------------------------
ReadSector
lda #$AA ; lots of custom RWTS routines
sta $31 ; need these zero page locations
lda #$AD ; set to magic values
sta $4E
lda gIsProtDOS
beq _protread
setuprwts
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ldy #<gRWTSParams
lda #>gRWTSParams
callrwts jsr $FF00 ; modified at runtime (see Inspect1)
bcc endread
lda gOnAClearDayYouCanReadForever
beq setuprwts
endread
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rts
;
; "Protected.DOS" has enough differences that we just
; split everything out here. The hi/lo RWTS parameter
; table address is set in A/Y instead of Y/A. The
; RWTS entry point is $BA00. The third data prologue
; nibble is stored in zp$4E and varies based on track
; and sector.
;
!zone {
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_protread
lda gTrack ; T02,S05+ use "protected" mode
cmp #$03 ; (altered data prologue and
bcs .protected ; nibble translate table)
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cmp #$02 ; T00,S00 - T02,S04 use
bcc .standard ; "standard" mode
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lda gSector
cmp #$05
bcs .protected
.standard
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lda #$9B
sta $BF2C
bne .go ; unconditional branch
.protected
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lda #$B5
sta $4E
lda #$D5
sta $BF2C ; execution falls through here
.go
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lda #<gRWTSParams
ldy #>gRWTSParams
jsr $BA00 ; note non-standard entry point
bcc endprotread
lda gOnAClearDayYouCanReadForever
beq .go
endprotread
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rts
}
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gRWTSParams ; used to read each sector
!byte $01,$60,$01,$00
gTrack !byte $00
gSector !byte $00
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!word dct
gAddress !word $1F00
!byte $00,$00,$01,$00,$FE,$60,$01,$00,$00
dct !byte $00,$01,$EF,$D8,$00