S-DSP registers

The S-DSP registers are accessed via the DSPADDR and DSPDATA S-SMP registers.

S-DSP global register summary

Name		Address	Bits	Type	Notes
MVOLL	MVOL (L)	$0C	VVVV VVVV	RW	Left channel main volume, signed.
MVOLR	MVOL (R)	$1C	VVVV VVVV	RW	Right channel main volume, signed.
EVOLL	EVOL (L)	$2C	VVVV VVVV	RW	Left channel echo volume, signed.
EVOLR	EVOL (R)	$3C	VVVV VVVV	RW	Right channel main volume, signed.
KON		$4C	7654 3210	RW	Key on. Writing this with any bit set will start a new note for the corresponding voice.
KOFF	KOF	$5C	7654 3210	RW	Key off. Writing this with any bit set will put the corresponding voice into its release state.
FLG		$6C	RMEN NNNN	RW	Flags: soft reset (R), mute all (M), echo disable (E), noise frequency (N).
ENDX		$7C	7654 3210	R	Read for end of sample flag for each channel.
EFB		$0D	VVVV VVVV	RW	Echo feedback, signed.
-	-	$1D	---- ----	RW	Unused.
PMON		$2D	7654 321-	RW	Enables pitch modulation for each channel, controlled by OUTX of the next lower channel.
NON		$3D	7654 3210	RW	For each channel, replaces the sample waveform with the noise generator output.
EON		$4D	7654 3210	RW	For each channel, sends to the echo unit.
DIR		$5D	DDDD DDDD	RW	Pointer to the sample source directory page at $DD00.
ESA		$6D	EEEE EEEE	RW	Pointer to the start of the echo memory region at $EE00.
EDL		$7D	---- DDDD	RW	Echo delay time (D).
FIR0	C0	$0F	VVVV VVVV	RW	Echo filter coefficient.
FIR1	C1	$1F	VVVV VVVV	RW	Echo filter coefficient.
FIR2	C2	$2F	VVVV VVVV	RW	Echo filter coefficient.
FIR3	C3	$3F	VVVV VVVV	RW	Echo filter coefficient.
FIR4	C4	$4F	VVVV VVVV	RW	Echo filter coefficient.
FIR5	C5	$5F	VVVV VVVV	RW	Echo filter coefficient.
FIR6	C6	$6F	VVVV VVVV	RW	Echo filter coefficient.
FIR7	C7	$7F	VVVV VVVV	RW	Echo filter coefficient.
(table source)

There are 8 voices, numbered 0 to 7. Each voice X has 10 registers in the range $X0-$X9.

S-DSP voice register summary

Name		Address	Bits	Type	Notes
VxVOLL	VOL (L)	$X0	SVVV VVVV	RW	Left channel volume, signed.
VxVOLR	VOL (R)	$X1	SVVV VVVV	RW	Right channel volume, signed.
VxPITCHL	P (L)	$X2	LLLL LLLL	RW	Low 8 bits of sample pitch.
VxPITCHH	P (H)	$X3	--HH HHHH	RW	High 6 bits of sample pitch.
VxSRCN	SRCN	$X4	SSSS SSSS	RW	Selects a sample source entry from the directory (see DIR below).
VxADSR1	ADSR (1)	$X5	EDDD AAAA	RW	ADSR enable (E), decay rate (D), attack rate (A).
VxADSR2	ADSR (2)	$X6	SSSR RRRR	RW	Sustain level (S), sustain rate (R).
VxGAIN	GAIN	$X7	0VVV VVVV 1MMV VVVV	RW	Mode (M), value (V).
VxENVX	ENVX	$X8	0VVV VVVV	R	Reads current 7-bit value of ADSR/GAIN envelope.
VxOUTX	OUTX	$X9	SVVV VVVV	R	Reads signed 8-bit value of current sample wave multiplied by ENVX, before applying VOL.
(table source)

Register types:

• RW - Readable and Writable
• R - Readable (technically writable, but not intended to be written to)

References

• Anomie's S-DSP Doc
• ares source code, ares/sfc/dsp directory, by Near and ares team