FDS-N163 playback issues

[Gumball2415]

NSF export of this module crashes in Mesen2 @ commit 30ece8ec6271f09cffa440828a1c96e35fef837a
When assembled with .asm export and driver source, FDS automodulation isn't working.

details:

• build: release x64 Dn-FT v0.5.1.1+ beta @ commit 4493431

attachments:

• computer.dnm
• computer.nsf (NSF2 export)
• music.nsf (.asm export, compiled with driver v2.15)

investigation is needed.

[Gumball2415]

the latter is caused by #331

[Gumball2415]

the former is caused by the memory region in $8000-DFFF becoming read-writeable by FDS. in some NSF players where they do not make this region read-writeable, the NSF works as expected, but when exported as NSF and played in Mesen, which makes the region read-writeable, the program crashes through a cascade of expansion audio register writes overwriting driver code.

example case using this NSF: computer.zip

the NSF is exported with a "glob" multichip configuration, enabling all expansion audio code. (USE_ALL)

VRC6 initialization writes $00 to $9003.

Dn-FamiTracker/Source/drivers/asm/init.s

Lines 98 to 101 in 12399c0

	.if .defined(USE_VRC6)
	lda #$00
	sta $9003
	.endif

N163 writes to $0E $C000 due to 5B being enabled. this prevents conflicts with 5B registers.

Dn-FamiTracker/Source/drivers/asm/n163.s

Lines 66 to 71 in 12399c0

	; Enable sound, copied from PPMCK and verified on a real Namco cart
	; no sound without this!
	.if .defined(USE_S5B) ;;; ;; ;
	lda #$0E
	sta $C000
	.endif ; ;; ;;;

VRC7 init writes to $9010 and $9030, ending up with $3E and $00 in both registers respectively.

Dn-FamiTracker/Source/drivers/asm/vrc7.s

Lines 30 to 46 in 12399c0

	ft_init_vrc7:
	lda #$00
	sta var_ch_vrc7_PatchFlag
	tax
	: stx $9010
	jsr ft_vrc7_delay2
	sta $9030
	jsr ft_vrc7_delay
	inx
	cpx #$3F
	bne :-
	ldx #$05
	lda #$FF
	: sta var_ch_vrc7_EffPatch, x
	dex
	bpl :-
	rts

the former write corrupts this line to sta $3e20,x instead of sta $0420,x, which is where var_ch_PeriodCalcLo is compiled to.

Dn-FamiTracker/Source/drivers/asm/effects.s

Lines 220 to 224 in 12399c0

	ft_calc_period:
	; Load period
	lda var_ch_TimerPeriodLo, x
	sta var_ch_PeriodCalcLo, x

there are also memory corruptions throughout the driver, though i am not sure where they are coming from.

in any case, overwriting data/code results in nondeterministic behavior and may even cause the program to crash.

#334