mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-12-30 22:32:48 +00:00
0a84e76e4e
The ZX Spectrum (default for pt3 files) runs the AY-3-8910 at 1.77MHz. We do this by multiplying by 9/16 (which is a pain, but could be worse)
121 lines
3.7 KiB
Plaintext
121 lines
3.7 KiB
Plaintext
The PT3_player
|
|
~~~~~~~~~~~~~~
|
|
|
|
by Vince "Deater" Weaver
|
|
15 May 2019
|
|
http://www.deater.net/weave/vmwprod/pt3_player/
|
|
|
|
Plays Vortex Tracker II .pt3 files on the Apple II
|
|
|
|
|
|
Background
|
|
~~~~~~~~~~
|
|
Vortex Tracker is commonly used to create AY-3-8910 music for the
|
|
ZX Spectrum and Atari ST systems. A large number of great pt3 files
|
|
can be found on the internet.
|
|
|
|
There are many benefits to using .pt3 format, but until now there
|
|
was no player available for Apple II/6502. (Though some people
|
|
had been playing the files using a z80-card in their system).
|
|
Part of the challenge was the documentation for the format was
|
|
in Russian, and the only source-code available for .pt3
|
|
players were in uncommented z80 assembly or else Russian-commented
|
|
Pascal.
|
|
|
|
Why .pt3? Why not play YM5 files?
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
There are already many projects (including one of my own) for
|
|
playing the .YM file format, which is much simpler. It is just a
|
|
series of AY-3-8910 raw-register dumps which can quickly be sent
|
|
to the Mockingboard.
|
|
|
|
The issue is uncompressed YM5 files are really huge. So you have to
|
|
do some sort of decompression on the fly, and even then you are looking
|
|
at 32k+ or more of RAM. This might be fine on an Apple IIe with
|
|
128k of RAM, but I am targetting a II+ where I don't have that much
|
|
available.
|
|
|
|
A PT3 file is a tracker format, meaning a list of notes, patterns, and
|
|
ornaments and can be played in place. Once you load the music file and
|
|
the player, no additional RAM is needed at all. It does take more CPU
|
|
than playing a YM5 file.
|
|
|
|
|
|
Using the PT3_PLAYER
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The pt3_player.dsk should boot automatically.
|
|
|
|
Controls:
|
|
Right/Left arrow Switch songs
|
|
Spacebar Pause playback.
|
|
M Switch from 1MHz to 1.77MHz mode
|
|
|
|
FUTURE FEATURES:
|
|
Key to disable visualization
|
|
Key to skip ahead/back in pattern list
|
|
L to enable looping in the song
|
|
|
|
ZX Compatability:
|
|
~~~~~~~~~~~~~~~~~
|
|
|
|
ZX Spectrum songs expect a 1.77MHz AY-3-8910, but the Apple II
|
|
is 1MHz so by default songs would sound lower
|
|
pitched. By default now we multiply by 9/16 to scale
|
|
things properly, but that does eat up extra CPU cycles.
|
|
You can toggle this on/off by pressing "M" when playing.
|
|
|
|
In theory we can create songs that expect 1MHz, but the pt3 format
|
|
has no way of indicating this.
|
|
|
|
Adding other files
|
|
~~~~~~~~~~~~~~~~~~
|
|
|
|
Unlike YM5 players which require complicated preparation of files
|
|
(with often complex, or hard-to find tools) the PT3_PLAYER can in
|
|
theory play plain .pt3 files.
|
|
|
|
To get the player to play them, just rename them to fit the naming
|
|
scheme (I think it will just be 00.PT3, 01.PT3, 02.PT3) and replace
|
|
the existing files on the disk image with your favorite Apple II
|
|
disk tool.
|
|
|
|
|
|
Code Optimization
|
|
~~~~~~~~~~~~~~~~~
|
|
|
|
The original working code is about 4k (not counting the pt3 file)
|
|
and has an overhead of roughly 20% when playing a song interrupt-driven
|
|
at 50Hz.
|
|
|
|
I'm keeping some stats here as I try to optimize the size and speed.
|
|
|
|
Song: "Summer of Rain"
|
|
~~~~~~~~~~~~~~~~~~~~~~
|
|
lz4 compressed
|
|
pt3 size: raw size: ym5 size: pt3.lz4:
|
|
3871 137015 7637 1793
|
|
|
|
Decoder Type size ZP use decode total CPU overhead
|
|
-------------------------------------------------------------
|
|
Original 4k(?) 22B 28.16s 171s 16%
|
|
|
|
|
|
Random Programming Reminders
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
ASR = CMP #$80 / ROR
|
|
|
|
signed 8-bit comparison
|
|
see http://6502.org/tutorials/compare_beyond.html#2.2
|
|
|
|
SEC ; prepare carry for SBC
|
|
SBC NUM ; A-NUM
|
|
BVC LABEL ; if V is 0, N eor V = N, otherwise N eor V = N eor 1
|
|
EOR #$80 ; A = A eor $80, and N = N eor 1
|
|
LABEL
|
|
|
|
If the N flag is 1, then A (signed) < NUM (signed) and BMI will branch
|
|
If the N flag is 0, then A (signed) >= NUM (signed) and BPL will branch
|