Sequences, order lists, and a command that changes the instrument

The rung between M3 and M4, and the point of doing it before the format:
the engine learns the tracker's model with the tune still assembled in,
so M4 becomes serialising a thing that exists rather than designing a
thing that does not.

A voice no longer walks one long track. 0xFF now means THIS SEQUENCE
ended, and the voice takes the next address from an order list of its
own. That is where repetition comes from, and it costs no notation: the
bass plays the same sequence in the first bar and the last and it is
written once. Per voice rather than one shared table of four-column rows,
because a voice's order cursor is then a pointer it advances by itself -
the same LDD and STD move everything else here makes. Four columns is how
it reads, not how it is stored.

Sequences also carry COMMANDS, which take no tick: the reader acts and
reads the next event on the same boundary. One is defined, 0x80, which
plays the rest of that voice on another patch, and the other 125 values
are left alone. A patch change reshapes whatever is still ringing on the
voice and nothing can be done about that - a channel has one set of
parameters and a note in its release is using them - so it is a fact
about the hardware and the cure is a rest, which is the composer's.

The engine moved to Libraries/player.asm rather than being copied into
the test a second time, now that it is big enough to drift. Play supplies
the tune and the beat; the library supplies the scheduler, the patch
loader and a voice's state. Verified by rendering: bar for bar identical
across the move.

AND THE TEST FOUND A REAL FLAW IN THE FORMAT, which is the whole argument
for building the reader first. The order list ended with 0x0000, on the
reasoning that no sequence could live below the 0x3000 this program is
based at. True of a loaded program, false of a boot image whose data
starts at zero - so the first test written against it read its own first
sequence as the end of the list and played nothing at all. It is 0xFFFF
now, which mirrors the 0xFF ending a sequence and is impossible
everywhere: a sequence at 0xFF00 or above has fewer bytes left than it
needs. An address is a poor place to hide a flag unless the address is
impossible in every program, not just this one.

One order list in the test now really ends, because otherwise nothing
reached the terminator at all: every voice sat on a long rest and the
break went unnoticed. With it, breaking the test reads garbage past the
end and the counter sums two notes at 781 hertz.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Programs/CosmOS/README.md

@@ -720,7 +720,7 @@ from every assembly file in it. Several are old programs written for the bare ma
 | Life | Conway's Game of Life, which had to be taught to stop, since a program that never ends takes the shell with it. Polls the console between generations. |
 | Snake | A game. Draws a whole screen with cursor addressing and steers with single keys, asking the console once a frame and never waiting. |
 | Keys | The console interrupting rather than being asked. The only one that brings a vector of its own, which is what the version two format exists for. |
-| Play | Four voices on one clock, which is what music is and one channel cannot be. The timer keeps a tick and every voice keeps its own place in its own track and its own count of how much longer the note it is holding lasts, so the parts move at four different rates and share nothing but the beat. A track is pairs of bytes, what to play and how many ticks it lasts: 1 to 127 is a MIDI note, zero is a rest, and 255 ends it - MIDI stops at 127, so neither of those had to be invented. A note's duration is its whole life and the gate goes down when the count runs out, which means a gap between two notes is written as a rest rather than invented by the player out of some fraction it decided on. Each voice loads an instrument of its own before a note is played - an oboe for the melody, strings under it, a square wave for the bass and a kalimba for the arpeggio - out of the format SoundPatch writes, which the player reads as a count and that many parameter and value pairs and understands nothing else about. Four patches can be up at once because a patch belongs to its channel; Kalimba has an LFO switched off and the other three have one on, and under a device where the LFOs belonged to the whole machine the last patch loaded would have imposed its setting on every part. The tune is assembled in for now; reading one from a file is what makes it a player rather than a program with one song in it. It spends over ninety nine per cent of its time asleep, because a beat is something to be woken by rather than counted up to. |
+| Play | Four voices on one clock, which is what music is and one channel cannot be. The timer keeps a tick and every voice keeps its own place in its own track and its own count of how much longer the note it is holding lasts, so the parts move at four different rates and share nothing but the beat. A track is pairs of bytes, what to play and how many ticks it lasts: 1 to 127 is a MIDI note, zero is a rest, and 255 ends it - MIDI stops at 127, so neither of those had to be invented. A note's duration is its whole life and the gate goes down when the count runs out, which means a gap between two notes is written as a rest rather than invented by the player out of some fraction it decided on. Each voice loads an instrument of its own before a note is played - an oboe for the melody, strings under it, a square wave for the bass and a kalimba for the arpeggio - out of the format SoundPatch writes, which the player reads as a count and that many parameter and value pairs and understands nothing else about. Four patches can be up at once because a patch belongs to its channel; Kalimba has an LFO switched off and the other three have one on, and under a device where the LFOs belonged to the whole machine the last patch loaded would have imposed its setting on every part. A voice does not play one long track: it walks an ORDER LIST of its own, a table of sequence addresses, and takes the next one when a sequence runs out. That is where repetition comes from and it costs no notation - the bass plays the same sequence in the first bar and the last, written once. The four columns are how it reads and how a tracker would show it; per voice is how it is stored, because a voice's order cursor is then a pointer it advances by itself. A sequence can also carry commands, which take no time at all: 0x80 plays the rest of that voice on a different patch, which is how the melody's last bar becomes a swell rather than a reed. Nothing keeps the voices together except that their sequences add up to the same length, which is the first thing a compiler should check. The tune is assembled in for now; reading one from a file is what makes it a player rather than a program with one song in it, and the engine that plays it is Libraries/player.asm rather than this program. It spends over ninety nine per cent of its time asleep, because a beat is something to be woken by rather than counted up to. |
 | Say | Prints whatever it was told, which is the shortest thing that shows osArgument working. |
 | Reboot | Starts the machine again, in 45 bytes. Writes a port rather than asking the system, because a reset has to work when the system does not. |
 | Once | Asks the loader to start something else on the next start, and only that one, in 569 bytes. |