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This Apple DA: Verify that a RW card is present. Resolves #78

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This commit is contained in:
Joshua Bell 2018-04-28 09:46:33 -07:00
parent bbe1fd0c33
commit 1e16555b11
1 changed files with 57 additions and 12 deletions
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69
desk.acc/this.apple.s
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@ -1077,8 +1077,14 @@ notpas:
;;; and installed chips.
;;; AE RamWorks cards can only support 8M max (banks $00-$7F), but
;;; the various emulators support 16M max (banks $00-$FF).
;;;
;;; If RamWorks is not present, bank switching is a no-op and the
;;; same regular 64Kb AUX bank is present throughout the test, so
;;; we also need to distinguish that case.
.proc check_ramworks_memory
sigb0 := $00
sigb1 := $01
;; Run from clone in main memory
php
sei ; don't let interrupts happen while the memory map is munged
@ -1090,34 +1096,73 @@ notpas:
RWBANK := $C073
ldx #0 ; bank we are checking
ldy #0 ; bank count
ldy #0 ; populated bank count
loop: stx RWBANK ; select bank
lda $00 ; save existing data
lda sigb0 ; save existing data
pha ; on stack
lda $01
lda sigb1
pha
txa ; bank number as first check byte
sta $00
cmp $00
sta sigb0
cmp sigb0
bne :+
eor #$FF ; bank complement as secondary check byte
sta $01
cmp $01
sta sigb1
cmp sigb1
bne :+
iny ; found a bank, count it
: pla ; restore saved data
sta $01
sta sigb1
pla
sta $00
sta sigb0
inx ; next bank
bne loop ; if we hit 256 banks, make sure we exit
;; Switch back to RW bank 0 (normal aux memory)
done: lda #0
lda #0
sta RWBANK
;; --------------------------------------------------
;; Y=0 means either 256 populated banks, or that there was
;; never a RawWorks card present and RWBANK is a no-op.
cpy #0
bne done
;; Disambiguate these cases by writing to banks 0 and 1
;; and testing that they work. We know that bank 1 is
;; not an unpopulated RW bank.
lda sigb0 ; Write signature to bank 0
pha
lda #0
sta sigb0
lda #1 ; Write signature to bank 1
sta RWBANK
lda sigb0
pha
lda #1
sta sigb0
lda #0 ; Check signature in bank 0
sta RWBANK
cmp sigb0 ; If we don't see bank 0 signature
beq :+ ; then this was all a sham; set Y
iny ; to 1 bank, i.e. normal AUX memory.
: lda #1 ; Restore bank 1
sta RWBANK
pla
sta sigb0
lda #0 ; Restore bank 0
sta RWBANK
pla
sta sigb0
;; Back to executing from aux memory
sta RAMRDON
done: sta RAMRDON
sta RAMWRTON
plp ; restore interrupt state
rts