mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-12-30 22:32:48 +00:00
103 lines
3.8 KiB
Plaintext
103 lines
3.8 KiB
Plaintext
The PT3_player Library version 0.2
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
by Vince "Deater" Weaver <vince@deater.net>
|
|
http://www.deater.net/weave/vmwprod/pt3_lib/
|
|
|
|
Last Update: 28 December 2019
|
|
|
|
Plays Vortex Tracker II .pt3 files on the Apple II
|
|
|
|
Background:
|
|
~~~~~~~~~~~
|
|
|
|
This code is meant as a relatively simple, reasonably optimized version
|
|
of the PT3 Vortex-Tracker player for use in other programs.
|
|
|
|
For some more background on this you can watch the talk I gave
|
|
at Demosplash 2019 on this topic.
|
|
|
|
|
|
What is a PT3 file?
|
|
~~~~~~~~~~~~~~~~~~~
|
|
|
|
A PT3 file is a tracker format with a compact file size used on systems
|
|
with AY-3-8910 based audio. This is most commonly the ZX-spectrum
|
|
and Atari ST machines.
|
|
|
|
Originally most PT3 players were in z80 assembly language for use on Z80
|
|
based machines. I have written code that will play the files on modern
|
|
systems (using C) and also the included code designed for the 6502-based
|
|
Apple II machines with Mockingboard sound cards installed.
|
|
|
|
You can find many pt3 files on the internet, or you can use the
|
|
VortexTracker tracker to write your own.
|
|
|
|
|
|
Using the Code (irq driven):
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
See the "pt3_test.s" example.
|
|
|
|
The code is in cc65 6502 assembly language but should be relatively
|
|
easy to port to other assemblers.
|
|
|
|
To get a pt3 file playing:
|
|
+ Optionally include "pt3_lib_mockingboard_detect.s" and
|
|
call "mockingboard_detect" and "mockingboard_patch" if
|
|
you want to auto-detect which slot the mockingboard is in.
|
|
Otherwise it will default to Slot#4
|
|
The patch code does a vaguely unsafe find/replace of $C4
|
|
live patch of the slot values, if you want a safer (but much
|
|
larger) version you can go into the file and ifdef out
|
|
the right code.
|
|
+ Be sure to either include the pt3 file as a binary, or load
|
|
it from disk to a buffer pointed to by PT3_LOC.
|
|
Not the beginning of the song needs to be aligned on
|
|
a page boundary (this makes the decode code a bit
|
|
more simple)
|
|
+ If you want to make the code more compact but use a lot of
|
|
the zero page, you can set PT3_USE_ZERO_PAGE in
|
|
"pt3_lib_core.s" This will use zp $80-$FF
|
|
but make the pt3 code a bit faster/smaller
|
|
+ You can set the interrupt speed in pt3_lib_mockingboard_setup.s
|
|
Generally files you find online are 50Hz.
|
|
For less overhead you can set something like 25Hz but
|
|
in that case you'll want to adjust the speed in the
|
|
tracker otherwise the songs will play at the wrong speed.
|
|
+ Vortex tracker by default assumes a system with a 1.77MHz
|
|
clock and sets frequencies accordingly. The Mockingboard
|
|
runs at 1MHz, so the pt3_lib converts on the fly.
|
|
For less overhead you can have the tracker generate
|
|
1MHz music and strip out the 1.77MHz conversion code.
|
|
+ If you want the music to Loop then set the LOOP value to 1.
|
|
|
|
|
|
Using the Code (cycle-counted):
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
I started work on a cycle-counted (deterministic cycle count) pt3
|
|
decoder, but it turned out to be large and complex enough to not be
|
|
worth the trouble.
|
|
|
|
You can still use pt3 files in cycle-counted demos. See the
|
|
../demosplash2019/ directory for an example. What this code does
|
|
is decode the pt3 files to memory during non-cycle-counted times,
|
|
and then use a deterministic playback function to play back this music.
|
|
Each frame of music decodes to 11bytes of register info, which means
|
|
at 60Hz you can get roughly 4s of music per 3kB of RAM.
|
|
|
|
|
|
Overhead:
|
|
~~~~~~~~~
|
|
|
|
It depends exactly on what features you use, but in general it will use
|
|
around 3KB of RAM plus the size of the PT3 file (which is often a few K).
|
|
Playback overhead depends on the complexity of the sound file but is typically
|
|
in the 10% to 15% range when playing back at 50Hz.
|
|
|
|
The player also uses 26 zero-page locations. More compact/faster code
|
|
can be generated if you're willing to sacrifice 128+ zero page locations.
|
|
|
|
|