Mucom88/PC88 (OPNA)
------------
Main Header
-----------
1 byte  - unknown (always 00)
2 bytes - FM Instrument List Offset
2 bytes - SSG Instrument List Offset? [missing in Misty Blue and other early variants]
x bytes - Sequence Header

Note: Since the sequence header matches in all variants, its offset can easily detected by
      searching for "2F 00" (FM1 channel pointer). The sequence header begins 1 byte earlier.


FM Instrument List
------------------
1 byte  - Instrument Count
x bytes - FM Instrument Data (19h bytes per instrument)

FM Instrument Register List:
30 34 38 3C 40 ... 88 8C B0


Sequence Header
---------------
1 byte  - YM2612 Timer B setting (for Tempo)
4 bytes - FM 1 channel pointers
4 bytes - FM 2 channel pointers
4 bytes - FM 3 channel pointers
4 bytes - SSG 1 channel pointers
4 bytes - SSG 2 channel pointers
4 bytes - SSG 3 channel pointers
4 bytes - OPNA Rhythm channel pointers
4 bytes - FM 4 channel pointers
4 bytes - FM 5 channel pointers
4 bytes - FM 6 channel pointers
4 bytes - ADPCM channel pointers
2 bytes - EOF Pointer
-> 2Eh bytes


Channel Pointers
----------------
2 bytes - start pointer
2 bytes - loop pointer

All pointers are relative to the sequence header, i.e. file offset 0005h.


Commands
--------
00		Track End
01-7F on	Octave o, Note n, Length xx
80-EF		Delay (xx & 7F)

F0 ii		Set Instrument
F1 vv		Set Volume
F1 gg c1 c2 c3 c4 c5 c6
		[OPNA Rhythm] Set volume
			gg - global rhythm volume
			c1-c6 - volume of channel 1-6
F2 xx xx xx	Set Detune
F3 xx		xx = 00..03: early Note Stop (stop note xx ticks earlier)
		xx = 04+: Set Echo Volume
		[Rhythm] Set OPNA Rhythm Channel Mask
			Bit 0 (01): Bass Drum
			Bit 1 (02): Snare Drum
			Bit 2 (04): Top Cymbal
			Bit 3 (08): Hi-Hat
			Bit 4 (10): Tom
			Bit 5 (20): Rom Shot
F4 00 dd pp uutt ss	Set Modulation
		Delay = dd ticks
		Speed = pp
		Delta = ttuu
		Steps until Delta Inversion = ss
F4 01		Disable Modulation
F5 bbaa		Loop Start Marker (bbaa = pointer to Loop Count, relative to pointer)
		-> increases Loop Stack pointer
F6 xx tt bbaa	Loop Exit at xx, Loop tt times back to bbaa
		bbaa is relative to the offset of the pointer.
F7 xx
F8 xx
F9 pp		Set Pan (OPNA Stereo Bits)
		pp = 01 - right speaker (OPN setting 40)
		pp = 02 - left speaker (OPN setting 80)
		pp = 03 - both speakers (OPN setting C0)
FA rr dd	FM Register Write (to port of current channel, rr - register, dd - data)
FA 26 tt	set FM Timer B to tt (controls Tempo)
FA aa bb cc dd ee ff
		SSG Register Write?? (could also be envelope setup)
FB vv		Change Volume by vv
FC xx xx xx
FD		Hold Note
FE bbaa		Loop Exit (bbaa = pointer to Loop Exit Counter, relative to pointer)
		-> jump to Loop End when current loop counter == first counter
FF		Master Loop Marker??
FF bbaa		[this variant can also be seen, though rarely]
