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modplayer.doc
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1991-05-08
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****** Instructions for using "modplayer.a", the stand-alone playroutine
****** of MED V3.10/OctaMED V1.00
"modplayer" is a piece of code (about 3 - 5 KBytes, depending on your needs)
which is linked with your program and plays modules made with MED.
"modplayer" contains the following routines:
InitPlayer
RemPlayer
PlayModule
StopPlayer
SetTempo
(As you can see, some of the less important functions of V2.10 are removed.
they are still available on medplayer.library.)
The arguments are passed in registers, and return values are returned in d0.
And now the descriptions of each one:
--------------------------------------------------------------------------
InitPlayer -- initialize everything
Before you can call the other functions, you must call this function.
It allocates the audio channels, timer, serial port (if MIDI) etc...
ARGUMENTS: none
RETURNS: 0 if everything is ok, otherwise something failed.
If something failed, you can still call the other
routines - they just don't do anything.
--------------------------------------------------------------------------
RemPlayer -- return everything back
Call this when your program exits. It frees the audio channels etc. etc.
ARGUMENTS: none
RETURNS: nothing
--------------------------------------------------------------------------
PlayModule -- start playing a module
When you want to start playing call this.
ARGUMENTS: a0 = pointer to the module. Where to get that pointer?
Don't panic, it's explained later....
RETURNS: nothing
--------------------------------------------------------------------------
StopPlayer -- stop playing
ARGUMENTS: no arguments
RETURNS: nothing
--------------------------------------------------------------------------
SetTempo -- set the playback tempo
ARGUMENTS: d0 = new tempo (1 - 240)
RETURNS: nothing
--------------------------------------------------------------------------
"modplayer.a" is the source code of the music routine. It contains stuff
that may be unnecessary for your purposes, that just takes time and memory.
There are some "switches" at the beginning of the source, that allow you
to turn off features you don't need. They are:
MIDI If the song(s) use(s) only the Amiga audio channels, set
this to 0.
AUDDEV For some purposes, you may want to disable the code that
allocates the audio channels using "audio.device", e.g.
in a non-multitasking environment. Normally this should
be 1.
SYNTH If the song(s) doesn't use synth/hybrid sounds, then this
can be set to zero.
CHECK This does some checkings to ensure that several values are
correct (e.g. is the sample in memory, no Amiga effects on
MIDI-tracks etc..). If you know that the song is correct,
you can safely turn the checks off.
RELVOL If you don't need the "relative volume", this can be zero.
IFF53 If the song doesn't contain IFF 3- or 5-octave samples,
this can be zero.
Timing
======
If you need vertical blanking timing, you can set VBLANK to 1 and CIAB to 0.
In normal use this is not recommended (because of the 16 % difference in
playing speed with NTSC and PAL Amigas).
Assembling
==========
Now you must assemble this file. The "modplayer.a" is directly compatible
with A68k V2.61 (or later...) and HiSoft Devpac 2. Other assemblers may need
some small work to assemble it correctly. The A68k V2.61 is available e.g.
on Fred Fish disk 314.
The result is an object file. Link this file with your program (add the name
of the .o-file to the .lnk-file)
Now you have the player, but there's still something missing...guess??...
that's right: the music.
You have two ways to get the music:
1. Include the module in your final executable.
2. Save the module as a separate disk file and load it when needed
(this is probably the best way if you have more than one song).
First I cover the first method:
--------------------------------------------------------------------------
Including the module in your final executable:
There are two ways to do this:
1. Save the module as an object file which you can directly link with your
program.
2. In some assemblers it is possible to include binary files into the code.
There's a special source "easyplayer.a" for Devpac 2 (see below...)
Again I cover the first method first:
You must load MED and then load the song you want to include. Now select
"Save song". You should see the save format requester. There are two
gadgets which save object files: "Obj 1" and "Obj 2". Another problem,
which one to select??
Well, the reason why there are two gadgets is that Lattice's Blink 5.04,
which I use, handles the chip bits of the object files in a different way
to the description in AmigaDOS manual.
While the the "AmigaDOS-manual" way would be
000003EA 40001234,
hunk_data | hunk size
chip
Blink uses a format like this:
400003EA 00001234
| hunk_data hunk size
chip
The "Obj 1" gadget saves the file in Blink format, "Obj 2" saves it in
the "AmigaDOS manual-format".
I suggest that you first try "Obj 1". If you get an error message when
linking, then select "Obj 2".
Now you know how to save the object file. The object file has exactly
one symbol defined: the module (struct MMD0). The name of the symbol
depends on the file name (so you can have more than one song). If the
file name you entered was "song", the object file would be "song.o" and
the module would be defined as "_song" (in C just plain "song").
In C, you would define it this way:
extern struct MMD0 far song; /* remember to include "modplayer.h" */
and to start playing, you'd call (assuming you've already called InitPlayer):
PlayModule(&song);
With assembler, it would look like this:
xref _PlayModule
xref _song
....
lea _song,a0
jsr _PlayModule(pc)
Then the another way...
When you have included the module (not an object file!!) as a binary
module, it must be relocated before it can be used. The easiest way to
do this is to use _RelocModule, which is in "loadmod.a". After it's
relocated, send the pointer of the module to PlayModule (NOTE: Remember
to xdef the _RelocModule-function or strip the function from loadmod.a).
By the way, never relocate the same module twice. It is 100 % guaranteed
that it won't work then.
And the second method (loading modules from disk):
--------------------------------------------------------------------------
File "loadmod.a" contains three routines:
LoadModule
UnLoadModule
RelocModule (see above)
You need only the first two of them. RelocModule is used by LoadModule.
--------------------------------------------------------------------------
LoadModule -- load module from disk
Loads and relocates module.
ARGUMENTS: a0 = pointer to the file name
RETURNS: d0 = pointer to the module, if something failed: 0
--------------------------------------------------------------------------
UnLoadModule -- free the module from memory
Frees the module. Remember to StopPlayer() before you unload the module
that is currently playing. Also remember to free all modules you've loaded
before you exit the program.
ARGUMENTS: a0 = pointer to the module (may be 0)
RETURNS: nothing, nothing and nothing
--------------------------------------------------------------------------
Just call LoadModule to load the module and send the returned pointer to
PlayModule. Easy??
==========================================================================
REMEMBER: All functions expect the arguments in registers. This is
automatically (??) handled by you when you program in
assembler, but it is not automatically handled when you
program in C.
If you have Lattice/SAS C V5.xx, this is done automatically if you include
"modplayer.h" in all your code modules which call modplayer. If you
have a compiler which doesn't support argument passing in registers,
then you have to write the stub routines in assembler.
That was it. See also the small example sources.
==========================================================================
easyplayer.a -- easy-to-use player for demos etc.
This is a player designed for playing a single song. It works on Devpac 2
(not on A68k, because it doesn't have INCBIN-command). To use it, insert
it into your code (or assemble separately and link). The name of the module
must be written into the INCBIN-statement. At the beginning of the program,
call _startmusic, when you're ready to finish, call _endmusic. That's all.