hpr-knowledge-base/hpr_transcripts/hpr1476.txt

Episode: 1476
Title: HPR1476: Sega Genesis Music Driver
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr1476/hpr1476.mp3
Transcribed: 2025-10-18 03:48:11

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A
Alright, that was a nice video.
Hello everybody, my name is Sikflup. Sikflup to this level that is, and you are listening
to Actra Public Radio. In this exciting edition of Actra Public Radio, we are going to be
talking about the Psychogenesis. Specifically, we're going to be interviewing Kibalus
about Kibalus 1 that is about his VGM driver. So what is a VGM driver you might be asking
about? Well, a bit of background is necessary. A bit of background about the Psychogenesis.
I was also known as the Mega Drive in European places. It was necessary. Well, the Psychogenesis
is a console that we all know and love. And inside of it, there's a bunch of chips. The
68,000 being the processor, the main processor in it. There's also another processor in it
called the Z80, and the Z80 has mapped onto its address space a FM chip, the YM2612, and
PSG, programmable sound generator, and those two sound chips generate music. And they have
the two sound chips kind of attached to the Z80 in some sense. And the 68K running. And
so the 68K can acquire the Z80 bus and have it mapped onto its address space in a little
peculiar area and upload a driver as it's known. To the Z80 memory, the Z80 memory primarily
being RAM and then reset the Z80. And so you can send the Z80 a program and have it run.
And that program typically runs sound, it's like a sound program. And so this is like a sound
driver. And so there's a particular sound encapsulation format called VGM. For video game music,
video game music being this, this, this file called a VGM file. And this is a driver for it
for the Sega Genesis. So let's get, let's get into the interview and hope you enjoy.
All right, everyone, we're here with Kibbles, and welcome.
Hello. How are you doing? Good, how are you doing?
That's not too bad. So rumor has a you wrote a pretty wicked VGM driver for the Sega Genesis.
How did you get into Sega Genesis programming? Well, I don't know. I just wanted to,
one of the consoles I had as a kid, I always thought it was pretty cool. And in fact,
I always wanted to do some, some kind of like retro kind of console development. And just like,
hey, I'll learn to program Sega Genesis. I think I wanted to do the Sega CD. I haven't quite got
there yet. But on the way, one of the, you know, one of the things I wanted to be able to do is
play music on it, so. Could you describe what VGM is for the audience?
Yes, it is a, well, it's the spec that describes chiptunes. There's a lot of different
there's a lot of different chips that can that that this works with. It's not just the
Sega Genesis. There's quite a number of different ones that it can use. And so that, you know,
that's pretty much it. That's up, you know, the instruments that define the songs, samples
in the songs. And then, you know, this is the notes on and off and changing the
decay rate of stuff. For adding, you know, special effect, like some echo or other effects to the
songs. I see. And, why VGM? Well, it looked, well, really, I, you know, I, I, I was starting
programming the just about a year and a half ago or so. And when I, I didn't really, you know,
no, I just knew that I, that I wanted to be able to do sound as well as graphics. I kind of
learned the basics of like the background sprites and that seems to be pretty well defined. But
how I would get sound and music into, into things wasn't clear to me. And especially things that
I could like make, not that I make very good stuff. But, and I use like a strictly like Linux
environment when I, when I, when I work. And so I stumbled, you know, across some like trackers.
And what, you know, one of them was like Deflamask and one of the outputs that has this, you know,
VGM format. And so that seemed well, that seems like, you know, the most convenient workflow I could
have would be to use, you know, to like Deflamask write songs, exported into VGM. And then if I had
a way I could load it in and play it, that'd be great. And then I saw that you wrote, you know,
you wrote that little VGM driver. I mean, it was, it was in SDCC. And it was really to the point,
and I was like, once I saw that, I got it. I was like, okay, that's actually not too hard. Except
I wanted it to be, you know, a little more just like, you know, like cover some of the edge cases.
And, you know, be able to load songs wherever I want. And so I just kind of basically took that core
that you wrote and just expanded by it. And what is SDCC for everyone? Small device decompiler.
And it hits, you know, cool little compiler for little chips like the Z80 and various other
8-bit chips and others. Yeah, it's a quite nice little compiler. I really like it personally.
And I never really used it till I saw those examples. And it just, you know, it seemed like they would,
you know, be perfect thing for that. And it looks like, you know, since then, you know, learned about
like the optimization, you can do with the compiler, like the people optimizations where I can tell
the compiler, hey, don't do this. Do what I tell you for this particular, you know,
way that you're creating this assembly.
I think that there's still a lot to be done, you know, with it. Because, I mean,
there's, you know, there's K, what you can do with the Z80, especially with C and something
like sound playback. It's almost at the point now where I want to just rewrite the whole thing
and straight assembly. And I've actually taken, like, large chunks of what's there. And there's
a lot of inline assembly right now. And it's kind of ugly.
Yeah, I looked at the code. It's, um, it's kind of hard to follow.
Yeah. And, you know, it started that, you know, I, it was, you know, the earlier versions of
drum was entirely just in C where we're a little easier to follow and they're just kind of filled
in all the different cases and did some initialization to figure out where and memory it was and
to do bank switching and all that. And it comes to a point where I was having, I would, I would
time out everything, you know, but how the C would be compiled in the assembly of waste a lot of
cycles. And it's really not a lot to waste. There's the, the chips not clocked very fast. And we
want to do as much kind of, especially with PC and playback. And that's the whole, that's, that's
the real track. It's built into the PC and playback. Um, and to hopefully do as much as you can.
I, I've currently limited to like eight kilohertz and just one sample playing at the time. And I
want to see that I think it's possible to increase that at least to have, you know, a couple samples
playing at once or sound effect and a sample. Really probably more could be done with some new ideas
that add some complexity to the whole process. And I don't, you know, I haven't, this is, you know,
probably the first Z80 assembly I've ever done. So I'm just kind of digging into it and learning.
What is, uh, what is the hardest thing in development?
Well, for one is there's so many files out there in VGMs, different permutations of, of ways
that this is represented. It's kind of come up with files that I can play and to cover the edge cases
so that there's not some song that doesn't play or that is hack the speed that it should be or
the sound effect that has, you know, weird noises finding and identifying that is, it's been tricky.
I have, you know, you know, kind of a number of them that tend to run through that to cover some
of these cases because the VGM format has been around for a while. It's changed several times and
you know, some people will incorporate a, you know, really old VGM file and they want to play it
on the driver. So I'd like it to work or they'll have a brand new one for that's, that's usually
the latest stack and, you know, like that's work too. And just making all those different versions
kind of play would be, you know, that's, that's been, uh, that's been tricky.
What is your, let me set up, look like.
Um, I, I'm running a, um, Ubuntu, um, 1204. Um, on, on my laptop and it is a, it's a Nasis Zen book
um, that I, that I use for, for most of my, most of my development. And yes, what do I do? I'm
still in 1204. Well, because I have everything very nicely running in, in 1204 right now and I have
some other special things and, and things I've done to Unity to like turn off, um, the touchpad
gestures because they drive me crazy. And, you know, mention that upgrade but it's, it's been
a pretty stable, uh, platform for me. That's my main development. Um, I use them, uh, for my,
for my editor and a screen, you know, I guess you could call that it's, you know, with my ID.
Um, so I usually have like, uh, you know, terminal open and I'll have screen running and I'll have,
you know, them session with, you know, code in it. Um, I'll have some other screens up and with, um,
either, you know, use like XXD and, and look at like the data and the VGM files and then I'll have
at least screen over, I can do builds and that's, that's pretty much how I work.
I couldn't help but notice that, um, um, I could be getting the acronym wrong here because I,
oh, I'd look at the acronym and I always forget, um, but I couldn't help but notice that the VGM
driver is in SGDK. I'm wondering how, did you approach, um, is it staff who maintains SGDK?
Staff who maintains that and, um, actually, it was just, it was just pulled in so, um,
staff just pulled it in originally. Uh, and I, I, I think I just posted on one of the forums like,
hey, this is what I am and, uh, you know, and before I knew it was like it was actually in there and
I thought that was pretty cool. Um, you know, just another thing about the open source projects,
these, you know, little little things are added to, and they become a part of bigger projects,
which I think is pretty neat. Um, and then I've, you know, message staff and gotten some
amino advice of what we could do to improve it. And I've added some more, more recently I've added,
um, the sound effects for, uh, to, to the VGM format and sped up, sped it up, um, significantly,
and that's why there's so much inline assembly and also made a, you know, better support older
versions of the SPAC. And that's more recently often been pulled into the SGDK toolkit.
So, um, SGDK is the Psychogenesis Development Kit. This is, uh, maintained by our friend staff.
And this is a development kit for the Psychogenesis, as the name would, um, state. Um,
I haven't really used it too much. Um, I know you're not the expert on it, but, um, the last time I
checked it was for DOS, um, is it, um, a Linux binary or is it a Linux library that you can compile?
Um, or how do you incorporate it in your development? That's a good question. Um, so, you know,
uh, one of the first things I did was try to set up a Linux environment. Now, there's a user,
um, uh, there's someone on the, on the forums, um, Chili Willie, um, who had, you know, a bunch of
steps. These are what you do to set up SGDK or, or really just to set up a Linux, um, development
environment. And you could also include SGDK because you can absolutely set up the Linux,
nevermind, or a genesis development, um, environmental Linux without SGDK and lots of people do.
Um, but you have to be able to do, you know, you have to have the, uh, you have to have, um,
GCC with, you know, build a, um, Motorola, um, 6800, um, you know, the right
assembler, it seemed to, you know, and a bunch of other tools, um, and ready to go.
Um, so I kind of like the idea of having also like a toolkit on top of that, so I don't have to
like write everything from scratch. I did a little bit of just kind of understanding how some of
those stuff works and straight assembly, but I'd, you know, might as well build upon the things
that other people have written when I can. And if I'm really interested, I'll dive into that
particular aspect. And so there's a, um, I took those, those, those steps and those scripts from
Chile, Willie, and I put it together into, you know, another little, just, I, it's like I'm
Google code, um, project and that compiled it for you. So really all you have to do is download,
or you just have to, um, you know, check out the, they're, they're the repo and type,
make to build the initial development environment and then you go into the SGDK sub directory and
every type of make SGDK and you have a fully functional Linux, um, Genesis development with SGDK
ready to go and imported it to freeBSD as well. So it should work there too.
That's, uh, that's right. Cool. Everyone, for everyone that, that's in the show notes and, um,
I'm probably going to close the interview here. Um, do you have anything else that you want to add?
Well, um, you know, a lot, all everything I've done here, um, it's, it's in, you know, it's in large
part and thanks to, um, all the people on, on the, on the sprite line forum, you know, without, without
all that information, I don't think I would have figured half of the stuff out or it would have
taken me a very long time. Oh yeah, yeah. The people on the forums are great.
Sometimes I feel embarrassed to ask questions, uh, but I try and get past that and ask them anyway.
And I think they're all pretty, you know, pretty accepting. I think, you know, there's only been a
few times when anyone's, even been, I like slightly rude to anyone, it's usually when it's cold
or, you know, they're, they're actually, they don't, they're very new, friendly, obviously, they,
they, they answered a lot of my questions and, and I'm, and I definitely was a new, um,
yes, it's, it's been very helpful. Okay, and that form link is in the show notes, everyone.
If you want to learn about Psychogenesis Development, that's the place to go and talk to everyone
in the community who is doing it. And, uh, thank you. And we will talk to you later.
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