N-SPC Engine/Source Variant ARAM Map

NOTE: This ARAM map only goes up to $800, which is the start of the SPC700 program. This is intended to show the purpose of the RAM-like memory locations that are used, which are stored prior to the start of this program.

NOTE 2: This is not a representative ARAM map for all N-SPC variants. However, a lot of these memory locations may be recycled, depending on the variant.

ARAM Address	Description
$00-$03	CPUIO register input.
$04-$07	CPUIO register output.
$08-$0B	Last value read by the CPUIO register.
$0C	Tick counter for the song to initialize itself.
$0D	Unused. However, its internal variable name in the source code is sf3c. sf0c is $0C's internal variable name in the source code. Thus, it's probably an initialization tick counter for something else.
$0E-$0F	Always zero. Read for an operation where YA needs to have its bits inverted.
$10-$13	Scratch RAM with varying purposes.
$14-$17	Scratch RAM mostly used for storing word addresses, though sometimes this isn't the case.
$18-$19	Contains an RNG value. Generated every timer 0 tick.
$1A	SFX voice on flag (AKA which music channels should not play notes)
$1B	Fast Forward flag.
$1C-$1F	Unused.
$20	Unused. However, its internal variable name in the source code is skc, and it appears to have been intended for a chs/soko-on routine, where the code is commented out in the source. TODO guess purpose
$21	Unused. However, its internal variable name in the source code is skdw, and it appears to have been intended for a chs/soko-on routine, where the code to call it is commented out in the source. TODO guess purpose
$22	Unused. However, its internal variable name in the source code is skd, and it appears to have been intended for a chs/soko-on routine, where the code to call it is commented out in the source. TODO guess purpose
$23	Unused. However, its internal variable name in the source code is skdadw, and it appears to have been intended for a chs/soko-on routine, where the code to call it is commented out in the source. TODO guess purpose
$24	Unused. However, its internal variable name in the source code is skdad, and it appears to have been intended for a chs/soko-on routine, where the code to call it is commented out in the source. TODO guess purpose
$25	Unused. However, its internal variable name in the source code is skca, and it appears to have been intended for a chs/soko-on routine, where the code to call it is commented out in the source. TODO guess purpose
$26	Unused. However, its internal variable name in the source code is skcb, and it appears to have been intended for a chs/soko-on routine, where the code to call it is commented out in the source. TODO guess purpose
$27	Unused. However, its internal variable name in the source code is skcs, and it appears to have been intended for a chs/soko-on routine, where the code to call it is commented out in the source. TODO guess purpose
$28-$2B	Unused. However, its internal variable name in the source code is bkc, and it appears to have been intended for a chc/bakuhatu-on routine, where the code to call it is commented out in the source. TODO guess purpose
$2C-$2D	Unused. However, its internal variable name in the source code is adk, and it appears to have been intended for a chd/sound effect routine, where the code to call it is commented out in the source. The variable itself is internally marked as kokaon add.. TODO guess purpose
$2E	Unused. However, its internal variable name in the source code is sac, and it appears to have been intended for a chd/sound effect routine, where the code to call it is commented out in the source. TODO guess purpose
$2F	Unused. However, its internal variable name in the source code is sacs, and it appears to have been intended for a chd/sound effect routine, where the code to call it is commented out in the source. TODO guess purpose
$30-$3F	Track pointer for the music, one word per track.
$40-$41	Phrase pointer.
$42	Phrase jump counter.
$43	Fractional counter for the CPUIO/SFX tempo ticker (running at a tempo of $20).
$44	Current channel being processed times 2.
$45	Key on flag for all channels. Cleared every timer tick.
$46	Key off flag for all channels. Cleared every timer tick.
$47	Voice bit being processed for music.
$48	FLG mirror.
$49	NON mirror.
$4A	EON mirror.
$4B	PMON mirror. Never set by the sound driver to anything other than zero, but clearly it sets up possible support by the programmer of the variant.
$4C	Counter to wait for the echo buffer to initialize itself for.
$4D	EDL mirror.
$4E	EFB mirror.
$4F	Unused.
$50	Global transposition.
$51	Fractional counter for the music tempo ticker.
$52	Fractional part of music tempo.
$53	Music tempo.
$54	Music tempo fade tick counter. Ends up reused as fractional part of target tempo once zero.
$55	Target music tempo.
$56	Music tempo fade rate per music tempo tick, fraction portion.
$57	Music tempo fade rate per music tempo tick, whole portion.
$58	Song volume, whole portion.
$59	Song volume, fraction portion.
$5A	Song volume fade tick counter. Ends up reused as fractional part of target song volume once zero.
$5B	Target song volume.
$5C	Song volume fade rate per music tempo tick, fraction portion.
$5D	Song volume fade rate per music tempo tick, whole portion.
$5E	Voice volume change flag.
$5F	Percussion base instrument ID. Defines the lowest instrument ID to use for the percussion kit.
$60	Fractional part of left echo volume.
$61	Left echo volume.
$62	Fractional part of right echo volume.
$63	Right echo volume.
$64	Left echo volume fade rate per music tempo tick, fraction portion.
$65	Left echo volume fade rate per music tempo tick, whole portion.
$66	Right echo volume fade rate per music tempo tick, fraction portion.
$67	Right echo volume fade rate per music tempo tick, whole portion.
$68	Echo volume fade tick counter.
$69	Target left echo volume.
$6A	Target right echo volume.
$6B-$6F	Unused.
$70,$72,$74,$76,$78,$7A,$7C,$7E	Music note duration, one byte per track.
$71,$73,$75,$77,$79,$7B,$7D,$7F	Music note duration after quantization.
$80,$82,$84,$86,$88,$8A,$8C,$8E	Subroutine loop counter.
$81,$83,$85,$87,$89,$8B,$8D,$8F	Unused.
$90,$92,$94,$96,$98,$9A,$9C,$9E	Track volume fade tick counter, one byte per track.
$91,$93,$95,$97,$99,$9B,$9D,$9F	Track panning fade tick counter, one byte per track.
$A0,$A2,$A4,$A6,$A8,$AA,$AC,$AE	Pitch slide tick counter.
$A1,$A3,$A5,$A7,$A9,$AB,$AD,$AF	Pitch slide delay in music tempo ticks.
$B0,$B2,$B4,$B6,$B8,$BA,$BC,$BE	Vibrato tick counter.
$B1,$B3,$B5,$B7,$B9,$BB,$BD,$BF	Maximum pitch offset for vibrato.
$C0,$C2,$C4,$C6,$C8,$CA,$CC,$CE	Tremolo tick counter.
$C1,$C3,$C5,$C7,$C9,$CB,$CD,$CF	Maximum volume offset for tremolo.
$D0-$EF	Unused.
$100,$102,$104,$106,$108,$10A,$10C,$10E	Vibrato fade tick counter.
$101,$103,$105,$107,$109,$10B,$10D,$10F	Unused.
$110-$1CF	Reserved for stack.
$1D0-$1DF	Unused mirrors for the SPC700 registers (referring to $F0-$FF). The TEST register is not defined in the original source, while the others are.
$1E0-$1FF	Unused.
$200,$202,$204,$206,$208,$20A,$20C,$20E	Saved note duration for music.
$201,$203,$205,$207,$209,$20B,$20D,$20F	Quantization, which is in 256ths of a note.
$210,$212,$214,$216,$218,$21A,$21C,$21E	Note velocity.
$211,$213,$215,$217,$219,$21B,$21D,$21F	Current instrument ID.
$220,$222,$224,$226,$228,$22A,$22C,$22E	Pitch base multiplier, whole portion.
$221,$223,$225,$227,$229,$22B,$22D,$22F	Pitch base multiplier, fraction portion.
$230-$23F	Pointer to return to once exiting the subroutine and all loops have been executed. One word per track.
$240-$24F	Start of subroutine pointer, used when looping. One word per track.
$250-$27F	Unused.
$280,$282,$284,$286,$288,$28A,$28C,$28E	Pitch envelope slide length in music tempo ticks.
$281,$283,$285,$287,$289,$28B,$28D,$28F	Number of music tempo ticks to delay the pitch envelope for.
$290,$292,$294,$296,$298,$29A,$29C,$29E	Pitch envelope sign.
$291,$293,$295,$297,$299,$29B,$29D,$29F	Pitch envelope offset in semitones.
$2A0,$2A2,$2A4,$2A6,$2A8,$2AA,$2AC,$2AE	Current vibrato pitch offset.
$2A1,$2A3,$2A5,$2A7,$2A9,$2AB,$2AD,$2AF	Vibrato pitch offset per music tempo tick.
$2B0,$2B2,$2B4,$2B6,$2B8,$2BA,$2BC,$2BE	Vibrato delay in music tempo ticks.
$2B1,$2B3,$2B5,$2B7,$2B9,$2BB,$2BD,$2BF	Vibrato fade length in music tempo ticks.
$2C0,$2C2,$2C4,$2C6,$2C8,$2CA,$2CC,$2CE	Vibrato fade rate per music tempo tick. There is no fractional portion involved.
$2C1,$2C3,$2C5,$2C7,$2C9,$2CB,$2CD,$2CF	Target vibrato maximum pitch offset for fade in.
$2D0,$2D2,$2D4,$2D6,$2D8,$2DA,$2DC,$2DE	Current tremolo volume offset.
$2D1,$2D3,$2D5,$2D7,$2D9,$2DB,$2DD,$2DF	Tremolo volume offset per music tempo tick.
$2E0,$2E2,$2E4,$2E6,$2E8,$2EA,$2EC,$2EE	Tremolo delay in music tempo ticks.
$2E1,$2E3,$2E5,$2E7,$2E9,$2EB,$2ED,$2EF	Unused.
$2F0,$2F2,$2F4,$2F6,$2F8,$2FA,$2FC,$2FE	Transposition on a per-channel basis.
$2F1,$2F3,$2F5,$2F7,$2F9,$2FB,$2FD,$2FF	Unused.
$300,$302,$304,$306,$308,$30A,$30C,$30E	Fractional part of track volume for music.
$301,$303,$305,$307,$309,$30B,$30D,$30F	Track volume for music.
$310,$312,$314,$316,$318,$31A,$31C,$31E	Track volume fade rate per music tempo tick, fraction portion.
$311,$313,$315,$317,$319,$31B,$31D,$31F	Track volume fade rate per music tempo tick, whole portion.
$320,$322,$324,$326,$328,$32A,$32C,$32E	Target track volume.
$321,$323,$325,$327,$329,$32B,$32D,$32F	Final voice volume for music prior to adjustments just before writing to DSP.
$330,$332,$334,$336,$338,$33A,$33C,$33E	Fractional part of panning for music.
$331,$333,$335,$337,$339,$33B,$33D,$33F	Panning for music.
$340,$342,$344,$346,$348,$34A,$34C,$34E	Panning fade rate per music tempo tick, fraction portion.
$341,$343,$345,$347,$349,$34B,$34D,$34F	Panning fade rate per music tempo tick, whole portion.
$350,$352,$354,$356,$358,$35A,$35C,$35E	Target panning.
$351,$353,$355,$357,$359,$35B,$35D,$35F	Panning with phase inversion settings.
$360,$362,$364,$366,$368,$36A,$36C,$36E	Current note, fractional portion.
$361,$363,$365,$367,$369,$36B,$36D,$36F	Current note, whole portion.
$370,$372,$374,$376,$378,$37A,$37C,$37E	Pitch slide rate per music tempo tick, fraction of a note.
$371,$373,$375,$377,$379,$37B,$37D,$37F	Pitch slide rate per music tempo tick, whole note.
$380,$382,$384,$386,$388,$38A,$38C,$38E	Target note.
$381,$383,$385,$387,$389,$38B,$38D,$38F	Fine tune.
$390-$3FF	Unused.
$400,$402,$404,$406,$408,$40A,$40C,$40E	Channel mute flag.
$401,$403,$405,$407,$409,$40B,$40D,$40F	Unused.
$410-$7FF	Unused.