Mikmod for Dreamcast?

[Indiket]

Hi guys!

One good friend request me a re-port of a known good homebrew game (Super Methane Brothers). Maybe some folks remember it because it was ported by LTK a long time ago. Furthermore, I only found the binary release (and no source.... clearly a violation of the GPL licence!). Additionaly, that port lacks the sound, so I wanted to investigate the reason.

So, I managed to compile and run again the game (good!), but unfortunately, I have no music and sound. The game uses MikMod to reproduce the sounds (it loads from a RAW file, and outputs it). I looked at kos-ports, but mikmod is not ported.

I also tried with SDL_mixer 1.2.6 (it has a stripped version of Mikmod), but although it loads OK, there is no sound output. I think that part must be broken on DC.

So, does anybody got experience with that? Anyone has a working libmikmod library for Dreamcast? Or a functional SDL_mixer with mikmod? I read that BlackAura got a similar problem with a Jump 'n' Bump port, but I don't know how it ended... (was the port ended/published?)
viewtopic.php?f=34&t=32209&st=0&sk=t&sd=a

Thanks!

[Indiket]

After working with the port, I managed to obtain music and sound . I think the next code can be useful to anyone wanting to build Mikmod (it's a custom driver using the KOS Sound stream).

Code: Select all

/*	MikMod sound library
	(c) 1998, 1999, 2000 Miodrag Vallat and others - see file AUTHORS for
	complete list.

	This library is free software; you can redistribute it and/or modify
	it under the terms of the GNU Library General Public License as
	published by the Free Software Foundation; either version 2 of
	the License, or (at your option) any later version.
 
	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU Library General Public License for more details.
 
	You should have received a copy of the GNU Library General Public
	License along with this library; if not, write to the Free Software
	Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
	02111-1307, USA.
*/

/*==============================================================================

  $Id: drv_dc.c,v 1.3 2011/08/05 20:30:00 raph Exp $

  Driver that outputs a stream to the AICA SPU of a Dreamcast.

==============================================================================*/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "mikmod_internals.h"

#ifdef DRV_DC

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include <kos.h>
#include <dc/sound/stream.h>

/* Global variables */
static SBYTE sound_buffer[SND_STREAM_BUFFER_MAX]; //Limit by SPU of Dreamcast
static snd_stream_hnd_t shnd = -1;

static volatile int playing = 0;

static void DC_CommandLine(CHAR *cmdline)
{
}

//Always valid
static BOOL DC_IsThere(void)
{
	return 1;
}

//Stop SPU.
static void DC_PlayStop() {
	if (shnd!=-1) snd_stream_stop(shnd);
	playing = 0;
	VC_PlayStop();
}

//Init SPU.
static BOOL DC_PlayStart() {	
	snd_stream_start(shnd, md_mixfreq, 1);
	playing = 1;
	if(VC_PlayStart())
		return 1;
	return 0;
}

//Stop the buffer, and free resources.
static void DC_Exit() {
    if (shnd!=-1) snd_stream_stop(shnd);
	
    playing = 0;

    //Free the SPU stream.
    if (shnd!=-1) {
		snd_stream_destroy(shnd);
		shnd = -1;
    }
    snd_stream_shutdown();
    sq_clr( sound_buffer, 65536 );
	
    VC_Exit();
}

//Called by Mikmod, means that we should get data from the buffer.
static void DC_Update(void)
{
	snd_stream_poll(shnd); //Request more data using the DC callback
}

//Function called by the Dreamcast SPU (polling). 
//Retrieve the buffer information into "sound_buffer" variable.
void *sound_callback(snd_stream_hnd_t hnd, int len, int * actual)
{
   if (playing)
	{
		*actual = VC_WriteBytes(sound_buffer, len);
	}
	else
	{
		memset(sound_buffer,0,len);
		*actual = len;
	}
    
    return (uint16*)(sound_buffer);
}

static BOOL DC_Reset() {
	if (shnd!=-1) snd_stream_reinit(shnd,sound_callback);
	return 0;
}

//Init the SPU and the buffers.
//MikMod variables: _mm_errno, md_mode
static BOOL DC_Init(void) {
		
	if (VC_Init()) {
		return 1;
	}
		
	//spu_wave_stream: beginning
	if (snd_stream_init() < 0){
		_mm_errno=MMERR_OPENING_AUDIO;
		return 1;
	}
	
	//Prepare buffer with a callback
	shnd = snd_stream_alloc(sound_callback, SND_STREAM_BUFFER_MAX);
	if (shnd == SND_STREAM_INVALID){
		_mm_errno=MMERR_OPENING_AUDIO;
		return 1;
	}

	//Mikmod mode
	//md_mixfreq by default is 44100 (depends of app).
	md_mode |= DMODE_STEREO;

	return 0;
}

MIKMODAPI MDRIVER drv_dc={
	NULL,
	"DC",
	"Dreamcast AICA SPU driver v1.0",
	0,255,
	"dc",
	NULL,
	DC_CommandLine,
	DC_IsThere,
	VC_SampleLoad,
	VC_SampleUnload,
	VC_SampleSpace,
	VC_SampleLength,
	DC_Init,
	DC_Exit,
	DC_Reset,
	VC_SetNumVoices,
	DC_PlayStart,
	DC_PlayStop,
	DC_Update,
	NULL,
	VC_VoiceSetVolume,
	VC_VoiceGetVolume,
	VC_VoiceSetFrequency,
	VC_VoiceGetFrequency,
	VC_VoiceSetPanning,
	VC_VoiceGetPanning,
	VC_VoicePlay,
	VC_VoiceStop,
	VC_VoiceStopped,
	VC_VoiceGetPosition,
	VC_VoiceRealVolume
};

#else

MISSING(drv_dc);

#endif

/* ex:set ts=4: */

I did some test on real Dreamcast, and results were quite OK (although not perfect). I still don't know why, but there is some delay when playing the sounds (maybe half a second). Is that normal?

As you see, there are two different callbacks: one is the Mikmod callback (gets the buffer data), and "sound_callback" is the SPU callback that is feeding with the buffer data. The Mikmod callback is called by the application (every cycle), and the other one is called when I poll with "snd_stream_poll".

I think that there can be a kind of delay between the two callbacks... Ideas to solve delay are welcome
Oh, and also comments / opinions / suggestions / improvements

Thanks to PH3NOM for giving me the preliminar idea!

[Chilly Willy]

I did some test on real Dreamcast, and results were quite OK (although not perfect). I still don't know why, but there is some delay when playing the sounds (maybe half a second). Is that normal?

What size are your buffers? Don't forget about latency - streaming is usually about filling large buffers well ahead of time to avoid noise in the audio from other tasks interfering with audio processing, but that means that sound/music will not be played without a pretty severe latency.

[Indiket]

Buffer size is SND_STREAM_BUFFER_MAX capacity (65536 bytes), but according to the callback, the buffer is feeding with 'len' bytes (what is needing by the SPU). When I call snd_stream_start, KOS internally calls a prefill function to start storing data.

[Chilly Willy]

Sounds like KOS lets most of that buffer fill before it starts playing. Good for a music player, not so good for games. That's partly why I did my own double-buffer routine for Doom. I set my buffers to 1024 samples so the latency is only about 23 ms. That works fine with MIDI playing while also mixing up to 16 sounds, so you might consider something similar with mikmod.

[PH3NOM]

Buffer size is SND_STREAM_BUFFER_MAX capacity (65536 bytes), but according to the callback, the buffer is feeding with 'len' bytes (what is needing by the SPU). When I call snd_stream_start, KOS internally calls a prefill function to start storing data.

Correct. And realistically, pre-filling 65536 bytes introduces a significant latency.

Code: Select all

   //Prepare buffer with a callback
   shnd = snd_stream_alloc(sound_callback, SND_STREAM_BUFFER_MAX);

Change it to

Code: Select all

   //Prepare buffer with a callback
   shnd = snd_stream_alloc(sound_callback, SND_STREAM_BUFFER_MAX/4);

And the latency will be 1/4 of current implementation