4cade/src/hw.memcheck.a

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;------------------------------------------------------------------------------
; Has64K
; Checks whether computer has functioning language card (64K)
;
; in: none
; out: C clear if 64K detected
; C set if 64K not detected
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; all other flags and registers clobbered
; ROM in memory (not LC RAM bank)
;------------------------------------------------------------------------------
Has64K
+READ_RAM1_WRITE_RAM1
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lda #$AA ; test #1 for $D0 page
sta $D000
eor $D000
bne @no
lsr $D000 ; test #2 for $D0 page
lda #$55
eor $D000
bne @no
clc
+HIDE_NEXT_BYTE
@no sec
+READ_ROM_NO_WRITE
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rts
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;------------------------------------------------------------------------------
; Has128K
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; Checks whether computer has functioning auxiliary memory (128K)
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;
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; in: none
; out: C set if 128K detected
; C clear if 128K not detected
; all other flags and registers clobbered
; zp $80-$9F clobbered
; ROM in memory (not LC RAM bank)
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;
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; adapted from "Prince of Persia" by Jordan Mechner
; (c) 1989 Broderbund Software
; https://github.com/jmechner/Prince-of-Persia-Apple-II/blob/master/01%20POP%20Source/Source/BOOT.S#L119
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;------------------------------------------------------------------------------
Has128K
+READ_ROM_NO_WRITE
sta STOREOFF
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lda ROM_MACHINEID
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cmp #6
bne @no ; earlier than //e -> no 128K
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lda SLOT3STATUS
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bmi @no ; no 80-column card -> no 128K
ldx #@checklen
- lda @checker,x
sta $80,x
dex
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bpl -
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jmp $80 ; check if auxmem actually works
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@checker
lda #$EE
sta WRITEAUXMEM
sta READAUXMEM
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sta $0C00
sta $0800
lda $0C00
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cmp #$EE
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bne @no
asl $0C00
asl
cmp $0C00
bne @no
cmp $0800
bne @yes
@no clc
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+HIDE_NEXT_BYTE
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@yes sec
@finish sta WRITEMAINMEM
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sta READMAINMEM
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rts
@checklen=*-@checker