Instrument definitions

The first byte tell the type of the instrument:
0x00		Sample
0x01		Square 1
0x02		Square 2
0x03		Programmable waveform (channel 3)
0x04		Noise
0x05-0x07	Makes the game crash
0x08		Sample that isn't resampled (always playing at the engine's pitch, probably faster)
0x09-0x0C	Same as 0x01-0x04 as far as I can tell
0x40		Key split instrument (points to different sub-instruments depending on MIDI key)
0x80		Every Key split instrument / percussion (each MIDI key points to its own sub-instrument)


Sampled Instrument (0x00) format:
00 kk 00 pp xxxxxxxx aa dd ss rr
   |     |  |        |  |  |  |_} Release value (8-bit), lower = fastest release
   |     |  |        |  |  |          Disabled with 0x00
   |     |  |        |  |  |____} Sustain level (8-bit)
   |     |  |        |  |             Disabled with 0xFF
   |     |  |        |  |_______} Decay value (8-bit),  lower = faster decay
   |     |  |        |                Disabled with 0x00
   |     |  |        |__________} Attack value (8-bit), lower = slower attack
   |     |  |                         Disabled with 0xFF
   |     |  |___________________} Pointer to sample data
   |     |______________________} Panning (only used as percussion sub-instrument)
   |____________________________} MIDI key (only used as percussion sub-instrument) (usually 0x3C, mid-C in MIDI standard)

   
PSG Instrument (0x01-0x04) format:
cc kk tt ss
|  |  |  |_} Sweep control (only channel 1)
|  |  |          Disabled with 0x08
|  |  |____} Hardware time length control
|  |             Disabled with 0x00
|  |_______} MIDI key (usually 0x3C or 0x00, apparently have no effect)
|__________} Channel

If Square channel:
dd 000000
|_} Duty cycle
        0=12,5%, 1=25%, 2=50%, 3=75%

If Noise channel:
pp 000000
|_} Control of the noise's period (0 = 32767 samples, 1 = 127 samples)

If Programmable Waveform channel:
xxxxxxxx
|_} Pointer to 16-byte waveform data

aa dd ss rr
|  |  |  |_} Attack value (3-bit), higher = slower attack
|  |  |          Disabled with 0x00
|  |  |____} Decay value (3-bit), higher = slower decay
|  |             Disabled with 0x00
|  |_______} Sustain level (4-bit)
|                Disabled with 0x0F
|__________} Release value (3-bit), lower = fastest release
                 Disabled with 0x00


Dummy instruments are: 01 3C 00 00 02 000000 00 00 0F 00

See: Instrument definitions.txt


$08002000 subroutine:

::03004450:: (r0 parameter)
03004474: Pointer to ROM

::030055B0:: (r1 parameter)
030055C4:	Pointer to ROM

Instrument = 3004450ROM * 12 + 30055C4ROM

03004484 = Instrument type (byte0)
If instrument type == 80h:
	03004450 |= 80h
	03004490 = Pointer (word4)
If instrument type == 40h:
	03004450 |= 40h
	03004490 = Pointer0 (word4)
	03004494 = Pointer1 (word8)
If instrument <= 3Fh:
	03004450 &= 0Fh
	03004486 = PSG Hardware time length control (byte2)
With r1 = 03004484 & 07h
If r1 == 01h/02h:
	If Sweep control (byte3) hasn't 80h and has 70h:
		03004487 = Sweep control
	Else:
		03004487 = 08h (disable)
	03004488 = Duty cycle (word4) << 6
If r1 == 03h:
	With r0 = [Waveform data pointer (word04)]
	04000070 (SOUND3CNT_L) = 40h (Wave RAM Bank = 1)
	04000090 (WAVE_RAM) =  r0[0..10h]
	04000070 (SOUND3CNT_L) = 00h (1 Bank, RAM Bank = 0, Channel = off)
If r1 == 04h:
	03004488 = Noise period (word04) << 3
If r1 == 00h:
	03004488 = Sample data pointer (word04)
0300448C = ADSR (word08)
++03004474


$0800481C subroutine:  For instrument 80h

::03004180:: (r0 parameter)

r1 = Pointer + [[030041C4]+[03004181]]*12
r2 = [03004181]
r3 = [[030041C4]+[03004181]]*12
r4 = 0Ch
If 03004180 hasn't 70h:
	Pointer + 03004181*12
	030041B5 = byte01
	If byte03 == 0:
		03004186 = 40h
	Elseif byte03 >= 80h:
		03004186 = byte03 - 80h
Else:
	Pointer + [030041C4+03004181]*12