Written by Gau of the Veldt
For the general Famidev community
Uwaoo! Hi. I'm Gau. Me have a shiny thing. Very shiny... shiny... shiny... A little *shiny* box inside my SNES. It's called an SPC-700. This little shiny thing makes noise when told to do so by code inside the SNES. This little gizmo is the key to making any sound whatsoever with your SNES program.
The SPC-700 is a co-processor. This means it is a separate CPU inside the SNES with its own memory and instruction set. The SNES communicates with the SPC through four 8-bit I/O ports. When the appropriate information is sent on the I/O ports, the program in the SPC will recognize the signals and perform some action (it might be nothing at all).
The SPC has its own memory, instruction set, etc. You cannot put a program into the SPC simply by storing it into RAM. The SPC must be sent the program via it's I/O locations. When you first turn on the SNES, the SPC has an internal kernal of sorts that gives it the ability to bootstrap to a program sent over the I/O port. Provided you have such a program, you can send it to the SPC. When the SPC recieves your code it will jump to the execution address in its memory that you specify (it's not required to be the start of code). This is where your program gets control of the SPC, DSP and I/O ports.
The memory on the SPC is 64K (kilobytes that is, not kilobits) in size. The DSP is 16-bit and supports eight stereo channels, each independantly pannable Left to Right. Samples sent into the DSP aren't the normal raw smapling used on an Amiga or PC. The samples in the SPC are encoded in a compressed format (I will get more to that later). The designers only placed 32K of RAM into the SPC however, so the upper 32K is unusable.
When the SPC starts, it waits for a startup value to appear in location 2141, This is hexadecimal $CC. However, you must do this last or else the kernal will get incorrect location and size information. Before I go too much further with this, I should indicate the block structure the SPC recognizes as part of the transfer protocol:
WORD Length WORD Location BYTES Data
The SPC kernal will let you send any number of these blocks (ie: a MIDI implementation might use this to load appropriate patches for a song about to be played and then send the song).
When you've sent all blocks and want to start running code in the SPC, you send a zero-length block. There won't be any data. This block which contains only a 0 for length and a location will tell the kernal in the SPC that you're done sending and that it should jump to the program you just sent. The section below refers to this as the terminator block.
The transfer protocol is fairly straightforward.
Okay, so you've got an SPC program in the SPC, now what? First your program should have some means of accepting input from the SNES when it wants to change game music or play a sound effect. To do this, you need to be able to read or write values from or onto the I/O port from the SPC. On the SNES 65816 side, the I/O ports $2140-$2143. Inside the SPC, they're zero page locations $f4-$f7. Location $f4 is $2140, $f5 is $2141, etc.
Your code will want to check these ports. Your SPC program should detect values by writing a sentinel value to the port and wait for it to change. Then call the appropriate routine or effect the appropriate change. The reciever should have the task of using the sentinel to detect a change. If all the values are important, use two ports, send the byte out both ports and wait for the exclusive-or complement of the value sent to show up at one of the ports. This will be the reciever telling you it has recieved the next byte ok. The reciever should wait for both locations to become equivalent before attempting to get the next byte. This will ensure the reciever that the sender has placed a value onto the port.
Next, your program will want to make some noise to tell the world (and you) that it's there. To do this, you need to know about the SPC's samples and registers. I'll start with the registers, then talk about the samples.
These registers are directly accessible from your SPC code. They are the zeropage locations $f1-$ff.
$F1 SPCCON1 bits 0-2 timer enables (1=on), bits 4-5 are I/O port clear bits (11=clear all) $F2 SPCDRGA DSP Register Address latch. Write a value here to select a DSP register to read or modify. This register itself is write- only. $F3 SPCDDAT DSP Register Data register. Read or write this register to read/write the DSP register currently referred to in SPCDRGA. $FA-$FC SPCTMLT Timer latches - place a value into the registers. The timer counts up to your time from 0. When it hits, the associated SPCTMCT register will advance. $FD-$FF SPCTMCT 4-bit counters count timer hits on each timer respectively Note: Timer 2 ($FC,$FF) counts at 64 kHz while the other two count at 8 kHz.
To store a DSP setting, you set $F2 to the DSP register address to modify and then set $F3 to the value this register is to recieve.
These registers repeat for each voice (00v0), where v is a voice number from 0 to 7.
0000 Volume left 0001 Volume right 0002 Pitch low 0003 Pitch high (The total 14 bits of pitch height) 0004 SRCN Designates source number from 0- 255 (sample number) 0005 ADSR 1 0006 ADSR 2 0007 GAIN Envelope can be freely designated by your code ($1f here: ignore ADSR and just output using the volume settings) 000F FILTER Filter deisgnation for this voice
The remaining registers affect everything:
0008 ENVX Present val of envelope with DSP rewrites 0009 VALX Present wave height val 000C MASTVOLL Master volume ($7f is maximum), left channel 000D ECHO Echo feedback bits (1 for each voice) 001C MASTVOLR Master volume ($7f is maximum), right channel 002C ECHOVOLL Echo volume, left 002D PTCHMOD Pitch modulation enable bits 003C ECHOVOLR Echo volume, right 003D NOISEN Noise enable bits 004C KEYON Key-on (enable voice) bits 004D ECHOEN Echo enable bits 005C KEYOFF Key-off (mute voice) bits 005D SAMLOC Hi-byte of mem address for the sample directory table (contains start-address and loop-start offset) 006C VOXCON Misc voice control Bit 7: Reset (0=off) Bit 6: Mute (0=off) Bit 5: Echo (1=off) 006D ECHOLOC Echo waveform directory location (Same as $5d) 007D ECHODLY Echo delay enable bits
The samples for the SPC are stored in a compressed format known as BRR. Unlike raw samples, the SPC samples are divided into 9-byte blocks. Each block encodes the equivalent of 16 raw 16-bit samples. The block format is as follows:
rrrrffle 01 23 45 67 89 ab cd ef rrrr - granularity (known in SPC dox as "range"), 0-12 ff - filter designation
These are normally zero but have significance on the LAST block:
l - loop flagbit e - last chunk of sample
To convert a raw sample, it must first be padded to a multple of 16 and converted to a 16-bit signed waveform.
The granularity indicates the quantization level used for this block. Higher granularity values indicate SMALLER shifts in amplitude for the BRR nybbles in this block. Since a nybble only has a dynamic range from -8 to 7, the granularity is used to expand this:
Granulirity Nybbles produce dynamic range:
00 -00008 to 00007, in steps of 0001 01 -00016 to 00014, in steps of 0002 02 -00032 to 00028, in steps of 0004 03 -00064 to 00056, in steps of 0008 04 -00128 to 00112, in steps of 0016 05 -00256 to 00224, in steps of 0032 06 -00512 to 00448, in steps of 0064 07 -01024 to 00896, in steps of 0128 08 -02048 to 01792, in steos of 0256 09 -04096 to 03584, in steps of 0512 10 -08192 to 07168, in steps of 1024 11 -16384 to 14336, in steps of 2048 12 -32768 to 28672, in steps of 4096
As you can see, the SPC uses 16-bit waveforms. There is enough space in 32K to store 58,240 samples using this compression method about 4 seconds at 14.4 KHz (sorry, there's not quite enough space to do a real good CD quality sound track), ah, but then there's always the cartridge memory (24 MBits would hold 5.5 million samples - since the transfer gets a speed faster than playback you could double buffer and send stuff this way - this would give you about 6.5 minutes of digitized sound at CD quality in monaural recording. Stereo would halve these times).
To convert you look at the raw sample 16 samples at a time. For all waveform points in this sample you find a range (above) that fits in all the points. This is your granularity. You then use the step value to quantize each point down to one nybble. Then string these nybbles together, left to right. When this is done, you just create the header byte and append the eight additional bytes from the nybbles you just obtained. This has just converted 16 bytes of your sample to BRR format (Yay hoo!). Repeat the above procedure for the rest of the raw sample.
When recording for music, keep the recording rate at about 30 Khz to ensure that using the pitch value will give you a broad tonal range when using that sample as an instrument. You can forgo (skip) this rule if you're using multiple patching of the instrument to counter envelope and timbre distortion (but you still have to keep this in mind however) [BTW: multiple patching means recording the instrument several times, playing the instrument at different octaves for each recording] you then match the right patch to the playback octave when performing music (ie: on the SPC).
A higher recording rate gives better results after BRR conversion, as does using 16-bit samples as opposed to 8-bit samples.
The SPC-700 is a processor. That means that, just like the 68000, the SPC follows a program placed in its memory. This means to do music, you must either use a predefined routine from someone else or learn SPC-700 machine code. The latter isn't all that bad (the SPC instructions set kicks butt over the 65816's). There are functions for testing individual bits, changing individual bits, doing 16-bit BCD, multiplying and dividing. Additionally, there are also 16-bit instructions and the accumulator and Y register combine to form a 16-bit register (much like H and L on the Z80).
The easiest way to do SPC700 coding is with an assembler. However, there is a distinct lack of SPC-700 assemblers (as compared to 65816 assemblers which are all over the place). However the Famidev site has one good shareware assembler called TASM which is a table-based assembler (you can change the instruction set it assembles for). If you place my instruction set (called TASM07.TAB) into TASM, you can assemble SPC-700 code. The list follows. It is beyond the scope of this overview to go into detail about the SPC 700 assembly. Maybe in another document I will do exactly that.
Anyhoo, here's the SPC-700 TASM table:
=== "TASM07.TAB" === Cut me here ============================================== "TASM SPC-700 Assembler, " /* /* Defines the SNES's SPC-700 Instruction set /* Created by Gau of the Veldt /* /* There are no special instruction classes /* /* INSTR,ARGS,OPCODE,BYTES,MOD,CLASS,SHIFT,OR /* ADC A,(X) 86 1 NOP 1 ADC A,[*+X] 87 2 NOP 1 ADC A,#* 88 2 NOP 1 ADC A,*+X 95 3 NOP 1 ADCZ A,*+X 94 2 NOP 1 ADC A,*+Y 96 3 NOP 1 ADC A,[*]+Y 97 2 NOP 1 ADC A,* 85 3 NOP 1 ADCZ A,* 84 2 NOP 1 ADC *,#* 98 3 CSWAP 1 ADC *,* 89 3 CSWAP 1 AND A,(X) 26 1 NOP 1 AND A,[*+X] 27 2 NOP 1 AND A,#* 28 2 NOP 1 AND A,*+X 35 3 NOP 1 ANDZ A,*+X 34 2 NOP 1 AND A,*+Y 36 3 NOP 1 AND A,[*]+Y 37 2 NOP 1 AND A,* 25 3 NOP 1 ANDZ A,* 24 2 NOP 1 AND (X),(Y) 39 1 NOP 1 AND *,#* 38 3 CSWAP 1 AND *,* 29 3 CSWAP 1 AND1 C,* 4A 3 NOP 1 AND1 C,/* 6A 3 NOP 1 ASL A 1C 1 NOP 1 ASL *,X 1B 2 NOP 1 ASL * 0C 3 NOP 1 ASLZ * 0B 2 NOP 1 LSR A 5C 1 NOP 1 LSR *,X 5B 2 NOP 1 LSR * 4C 3 NOP 1 LSRZ * 4B 2 NOP 1 ROL A 3C 1 NOP 1 ROL *,X 3B 2 NOP 1 ROL * 2C 3 NOP 1 ROLZ * 2B 2 NOP 1 ROR A 7C 1 NOP 1 ROR *,X 7B 2 NOP 1 ROR * 6C 3 NOP 1 RORZ * 6B 2 NOP 1 BBC0 *,* 13 3 CREL 1 BBC1 *,* 33 3 CREL 1 BBC2 *,* 53 3 CREL 1 BBC3 *,* 73 3 CREL 1 BBC4 *,* 93 3 CREL 1 BBC5 *,* B3 3 CREL 1 BBC6 *,* D3 3 CREL 1 BBC7 *,* F3 3 CREL 1 BBS0 *,* 03 3 CREL 1 BBS1 *,* 23 3 CREL 1 BBS2 *,* 43 3 CREL 1 BBS3 *,* 63 3 CREL 1 BBS4 *,* 83 3 CREL 1 BBS5 *,* A3 3 CREL 1 BBS6 *,* C3 3 CREL 1 BBS7 *,* E3 3 CREL 1 BPL * 10 2 R1 1 BRA * 2F 2 R1 1 BMI * 30 2 R1 1 BVC * 50 2 R1 1 BVS * 70 2 R1 1 BCC * 90 2 R1 1 BCS * B0 2 R1 1 BNE * D0 2 R1 1 BEQ * F0 2 R1 1 CLR0 * 02 2 NOP 1 CLR1 * 22 2 NOP 1 CLR2 * 42 2 NOP 1 CLR3 * 62 2 NOP 1 CLR4 * 82 2 NOP 1 CLR5 * A2 2 NOP 1 CLR6 * C2 2 NOP 1 CLR7 * E2 2 NOP 1 SET0 * 12 2 NOP 1 SET1 * 32 2 NOP 1 SET2 * 52 2 NOP 1 SET3 * 72 2 NOP 1 SET4 * 92 2 NOP 1 SET5 * B2 2 NOP 1 SET6 * D2 2 NOP 1 SET7 * F2 2 NOP 1 CMP A,(X) 66 1 NOP 1 CMP A,[*+X] 67 2 NOP 1 CMP A,#* 68 2 NOP 1 CMP A,*+X 75 3 NOP 1 CMPZ A,*+X 74 2 NOP 1 CMP A,*+Y 76 3 NOP 1 CMP A,[*]+Y 77 2 NOP 1 CMP A,* 65 3 NOP 1 CMPZ A,* 64 2 NOP 1 CMP X,#* C8 2 NOP 1 CMP X,* 1E 3 NOP 1 CMP X,* 3E 2 NOP 1 CMP Y,#* AD 2 NOP 1 CMP Y,* 5E 3 NOP 1 CMP Y,* 7E 2 NOP 1 CMP (X),(Y) 79 1 NOP 1 CMP *,#* 78 3 CSWAP 1 CMP *,* 69 3 CSWAP 1 CBNE *+X,* DE 3 CREL 1 CBNE *,* 2E 3 CREL 1 DBNZ Y,* FE 2 R1 1 DBNZ *,* 6E 3 CREL 1 DAA YA DF 1 NOP 1 DAS YA BE 1 NOP 1 NOT1 * EA 3 NOP 1 XCN A 9F 1 NOP 1 MOV1 C,* AA 3 NOP 1 MOV1 *,C CA 3 NOP 1 DECW * 1A 2 NOP 1 INCW * 3A 2 NOP 1 CLRW * 5A 2 NOP 1 ADDW YA,* 7A 2 NOP 1 SUBW YA,* 9A 2 NOP 1 MOVW YA,* BA 2 NOP 1 MOVW *,YA DA 2 NOP 1 MUL YA CF 1 NOP 1 DIV YA,X 9E 1 NOP 1 EOR A,(X) 46 1 NOP 1 EOR A,[*+X] 47 2 NOP 1 EOR A,#* 48 2 NOP 1 EOR A,*+X 55 3 NOP 1 EORZ A,*+X 54 2 NOP 1 EOR A,*+Y 56 3 NOP 1 EOR A,[*]+Y 57 2 NOP 1 EOR A,* 45 3 NOP 1 EORZ A,* 44 2 NOP 1 EOR (X),(Y) 59 1 NOP 1 EOR *,#* 58 3 CSWAP 1 EOR *,* 49 3 CSWAP 1 EOR1 C,* 8A 3 NOP 1 DEC A 9C 1 NOP 1 DEC X 1D 1 NOP 1 DEC Y DC 1 NOP 1 DEC *,X 9B 2 NOP 1 DEC * 8C 3 NOP 1 DECZ * 8B 2 NOP 1 INC A BC 1 NOP 1 INC X 3D 1 NOP 1 INC Y FC 1 NOP 1 INC *,X BB 2 NOP 1 INC * AC 3 NOP 1 INCZ * AB 2 NOP 1 MOV X,A 5D 1 NOP 1 MOV A,X 7D 1 NOP 1 MOV X,SP 9D 1 NOP 1 MOV SP,X BD 1 NOP 1 MOV A,Y DD 1 NOP 1 MOV Y,A FD 1 NOP 1 MOV (X),(Y) 99 1 NOP 1 MOV (X)+,A AF 1 NOP 1 MOV A,(X)+ BF 1 NOP 1 MOV (X),A C6 1 NOP 1 MOV A,(X) E6 1 NOP 1 MOV Y,#* 8D 2 NOP 1 MOV X,#* CD 2 NOP 1 MOV A,#* E8 2 NOP 1 MOV [*+X],A C7 2 NOP 1 MOV [*]+Y,A D7 2 NOP 1 MOV A,[*+X] E7 2 NOP 1 MOV A,[*]+Y F7 2 NOP 1 MOV *+X,A D5 3 NOP 1 MOVZ *+X,A D4 2 NOP 1 MOV *+Y,A D6 3 NOP 1 MOV *+Y,X D9 2 NOP 1 MOV *+X,Y DB 2 NOP 1 MOV X,*+Y F9 2 NOP 1 MOV Y,*+X FB 2 NOP 1 MOV A,*+X F5 3 NOP 1 MOVZ A,*+X F4 2 NOP 1 MOV A,*+Y F6 3 NOP 1 MOV *,A C5 3 NOP 1 MOVZ *,A C4 2 NOP 1 MOV *,X C9 3 NOP 1 MOV *,X D8 2 NOP 1 MOV *,Y CC 3 NOP 1 MOV *,Y CB 2 NOP 1 MOV A,* E5 3 NOP 1 MOVZ A,* E4 2 NOP 1 MOV X,* E9 3 NOP 1 MOV X,* F8 2 NOP 1 MOV Y,* EC 3 NOP 1 MOV Y,* EB 2 NOP 1 MOV *,#* 8F 3 CSWAP 1 MOV *,* FA 3 CSWAP 1 OR A,(X) 06 1 NOP 1 OR A,[*+X] 07 2 NOP 1 OR A,#* 08 2 NOP 1 OR A,*+X 15 3 NOP 1 ORZ A,*+X 14 2 NOP 1 OR A,*+Y 16 3 NOP 1 OR A,[*]+Y 17 2 NOP 1 OR A,* 05 3 NOP 1 ORZ A,* 04 2 NOP 1 OR (X),(Y) 19 1 NOP 1 OR *,#* 18 3 CSWAP 1 OR *,* 09 3 CSWAP 1 OR1 C,* 0A 3 NOP 1 OR1 C,/* 2A 3 NOP 1 SBC A,(X) A6 1 NOP 1 SBC A,[*+X] A7 2 NOP 1 SBC A,#* A8 2 NOP 1 SBC A,*+X B5 3 NOP 1 SBCZ A,*+X B4 2 NOP 1 SBC A,*+Y B6 3 NOP 1 SBC A,[*]+Y B7 2 NOP 1 SBC A,* A5 3 NOP 1 SBCZ A,* A4 2 NOP 1 SBC (X),(Y) B9 1 NOP 1 SBC *,#* B8 3 CSWAP 1 SBC *,* A9 3 CSWAP 1 TCALL * 01 1 T1 1 4 F0 TSET1 * 0E 3 NOP 1 TCLR1 * 4E 3 NOP 1 CALL * 3F 3 NOP 1 PCALL * 4F 2 NOP 1 JMP [*+X] 1F 3 NOP 1 JMP * 5F 3 NOP 1 PUSH PSW 0D 1 NOP 1 PUSH A 2D 1 NOP 1 PUSH X 4D 1 NOP 1 PUSH Y 6D 1 NOP 1 POP PSW 8E 1 NOP 1 POP A AE 1 NOP 1 POP X CE 1 NOP 1 POP Y EE 1 NOP 1 NOP "" 00 1 NOP 1 BRK "" 0F 1 NOP 1 RET "" 6F 1 NOP 1 RETI "" 7F 1 NOP 1 CLRP "" 20 1 NOP 1 SETP "" 40 1 NOP 1 CLRC "" 60 1 NOP 1 SETC "" 80 1 NOP 1 EI "" A0 1 NOP 1 DI "" C0 1 NOP 1 CLRV "" E0 1 NOP 1 NOTC "" ED 1 NOP 1 SLEEP "" EF 1 NOP 1 STOP "" FF 1 NOP 1 === "TASM07.TAB" === Cut me here ==============================================
Anyways, enjoy this SPC-700 doc. It's been fun. If you want help or more info, you can either mail me via the Famidev (famidev@webcom.com) mailing list, or at my email location (gau@netbistro.com), or additionally through my mail gateway from my WWW page (http://www.netbistro.com/~gau).
E-Mail: gau@netbistro.com
WWW: http://www.netbistro.com/~gau