mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-10-10 08:23:49 +00:00
mode7: update writeup
This commit is contained in:
parent
9c9ab1c818
commit
669ae77959
Binary file not shown.
Before Width: | Height: | Size: 18 KiB After Width: | Height: | Size: 15 KiB |
@ -7,34 +7,37 @@
|
|||||||
\begin{document}
|
\begin{document}
|
||||||
|
|
||||||
\title{Making an 8k Low-resolution Graphics Demo for the Apple II}
|
\title{Making an 8k Low-resolution Graphics Demo for the Apple II}
|
||||||
\author{DEATER, AKA Vincent M. Weaver}
|
\author{by DEATER, AKA Vincent M. Weaver}
|
||||||
\date{}
|
\date{}
|
||||||
\maketitle
|
\maketitle
|
||||||
|
|
||||||
\section{Why would anyone do this?}
|
\section{Why would anyone do this?}
|
||||||
|
|
||||||
I was making an inside-joke filled game for my retro system of choice,
|
While making an inside-joke filled game for my retro system of choice,
|
||||||
the Apple II.
|
the Apple II, I needed to create a Final-Fantasy-esque
|
||||||
This involves a Final-Fantasy flying-over-the-planet scene, and while
|
flying-over-the-planet sequence.
|
||||||
I was originally going to fake this I found that it was just barely
|
I was originally going to fake this, but then I found that it was just barely
|
||||||
possible to achieve this in real time.
|
possible to achieve this in real time.
|
||||||
|
Once I got the code working I realized it would be great as part of a
|
||||||
Once I got it working I realized this would be great as part of a
|
|
||||||
graphics demo, so off on that tangent I went.
|
graphics demo, so off on that tangent I went.
|
||||||
This despite the fact that all I know about the demoscene I learned
|
This went well, despite the fact that all I know about the demoscene I learned
|
||||||
from a few viewings of the Future Crew Second Reality Demo plus some
|
from a few viewings of the Future Crew {\em Second Reality} demo mixed with
|
||||||
dimly remembered Commodore 64 and Amiga flamewars from a few decades ago.
|
dimly remembered Commodore 64 and Amiga flamewars.
|
||||||
|
|
||||||
|
% from a few decades ago.
|
||||||
% This started out as some SNES style mode7 pseudo-3d graphics code
|
% This started out as some SNES style mode7 pseudo-3d graphics code
|
||||||
% I came up with while working on my TF7 game. The graphics looked
|
% I came up with while working on my TF7 game. The graphics looked
|
||||||
% pretty cool, so I started developing a demo around it.
|
% pretty cool, so I started developing a demo around it.
|
||||||
|
|
||||||
To make thins even better, the code ended up being roughly around 8kB so a
|
%To make thins even better, the code ended up being roughly around 8kB so a
|
||||||
lot of time was wasted fitting it under that arbitrary size limitation.
|
%lot of time was wasted fitting it under that arbitrary size limitation.
|
||||||
|
|
||||||
So in the end this ends up being impressive mostly because so few people
|
While I hope you enjoy the description of the demo and the work that
|
||||||
have bothered to write demos for this particular platform.
|
went into it, I do suspect the whole enterprise is only of note
|
||||||
Though I must make a shout out to the FrenchTouch group whose Apple II
|
because so few people write demos for the Apple II platform.
|
||||||
|
%So in the end this ends up being impressive mostly because so few people
|
||||||
|
%have bothered to write demos for this particular platform.
|
||||||
|
I would like to make a shout out to the FrenchTouch group whose Apple II
|
||||||
demos put this one to shame.
|
demos put this one to shame.
|
||||||
|
|
||||||
% The codesize ended up being roughly around 8kB, so I thought I'd
|
% The codesize ended up being roughly around 8kB, so I thought I'd
|
||||||
@ -86,78 +89,91 @@ demos put this one to shame.
|
|||||||
|
|
||||||
\section{The Hardware}
|
\section{The Hardware}
|
||||||
|
|
||||||
The Apple II was introduced in 1977.
|
The Apple II was introduced in 1977.
|
||||||
This demo should run on an original system, though I do not
|
This demo should run on an original system, though I do not
|
||||||
have hardware that old to test on.
|
have hardware quite that old to test on.
|
||||||
Note this predates the Commodore 64 by five years.
|
I like to troll C64 fans by noting this predates the Commodore 64 by
|
||||||
|
five years.
|
||||||
|
|
||||||
{\bf CPU, RAM and Storage}
|
\vspace{1ex}
|
||||||
|
\noindent
|
||||||
|
{\bf CPU, RAM and Storage:}
|
||||||
|
|
||||||
The Apple II has a 6502 processor running at roughly 1.023MHz.
|
The Apple II has a 6502 processor running at roughly 1.023MHz.
|
||||||
|
Early models only shipped with 4k of RAM, but later 48k, 64k, and 128k
|
||||||
|
systems were common.
|
||||||
|
While the demo itself fits in 8k, it decompresses to a larger size and uses
|
||||||
|
a full 48k of RAM;
|
||||||
|
this would have been very expensive in 1977.
|
||||||
|
|
||||||
Early models only shipped with 4k of RAM, but later 48k, 64k, and 128k
|
Also in 1977 you would probably be loading this from cassette tape.
|
||||||
systems were common.
|
It would be another year before Woz's single-sided
|
||||||
The demo requires 48k; this would have been very expensive in 1977.
|
$5\frac{1}{4}$" Disk II came about (eventually offering 140k of
|
||||||
|
storage per side with the release of Apple DOS3.3 in 1980).
|
||||||
|
|
||||||
Also in 1977 you would probably be loading this from cassette tape, as
|
\vspace{1ex}
|
||||||
it would be another year before Woz's single-sided
|
\noindent
|
||||||
$5\frac{1}{4}$" Disk II came about (eventually offering 140k of
|
{\bf Sound:}
|
||||||
storage per side with the release of Apple DOS3.3 in 1980).
|
|
||||||
|
|
||||||
{\bf Sound}
|
The only sound available in a stock Apple II is a bit-banged speaker.
|
||||||
|
There was no timer interrupt; if you wanted music you had to cycle-count
|
||||||
|
via the CPU to get the waveforms you needed.
|
||||||
|
|
||||||
The only sound available is a bit-banged speaker.
|
The demo uses a Mockingboard soundcard which was introduced in 1981.
|
||||||
There was no timer interrupt,
|
This board contains dual AY-3-8910 sound generation chips connected via
|
||||||
if you wanted music you had to cycle-count via the CPU.
|
6522 I/O chips.
|
||||||
|
Each sound chip provides 3 channels of square waves as well as noise and
|
||||||
|
envelope effects.
|
||||||
|
|
||||||
This demo uses the Mockingboard soundcard which was introduced in
|
\vspace{1ex}
|
||||||
1981. This board is extremely simple, with dual AY-3-8910 sound
|
\noindent
|
||||||
chips controlled by 6522 I/O chips.
|
{\bf Graphics:}
|
||||||
Each chip provides 3 channels of square waves, with noise and
|
|
||||||
envelope effects available.
|
|
||||||
|
|
||||||
{\bf Graphics}
|
It is hard to imagine now, but the Apple II had nice graphics for its time.
|
||||||
|
Compared to later competitors, however, it had some limitations.
|
||||||
|
|
||||||
The Apple II had nice graphics for its time, with this time being
|
\begin{center}
|
||||||
around 1977. Otherwise it is quite limited.
|
\begin{tabular}{|c|c|}
|
||||||
|
\hline
|
||||||
|
Hardware Sprites & No \\
|
||||||
|
User-defined charset & No \\
|
||||||
|
Blanking interrupts & No \\
|
||||||
|
Palette selection & No \\
|
||||||
|
Linear framebuffer & No \\
|
||||||
|
Hardware scrolling & No \\
|
||||||
|
Hardware page flip & Yes \\
|
||||||
|
\hline
|
||||||
|
\end{tabular}
|
||||||
|
\end{center}
|
||||||
|
|
||||||
\begin{center}
|
The hi-res graphics mode was a complex mess of NTSC hacks by Woz.
|
||||||
\begin{tabular}{|c|c|}
|
You got approximately 280x192 resolution, with 6 colors available.
|
||||||
\hline
|
However the colors were from NTSC artifacts and there were limitations
|
||||||
Hardware Sprites & No \\
|
on which colors could be next to each other (in blocks of 3.5 pixels).
|
||||||
Linear framebuffer & No \\
|
There was plenty of fringing on edges, and colors changed depending on
|
||||||
User-defined charset & No \\
|
whether they were drawn at odd or even pixels.
|
||||||
Blanking interrupts & No \\
|
To add to the madness, the framebuffer is interleaved in a complex way,
|
||||||
Palette selection & No \\
|
and pixels are drawn least-significant-bit first (all of this to make
|
||||||
Hardware scrolling & No \\
|
DRAM refresh better and to shave a few 7400 series logic chips from the design).
|
||||||
Hardware page flip & Yes \\
|
You do get two pages of graphics, Page 1 is at
|
||||||
\hline
|
\$2000\footnote{On 6502 systems hexadecimal values are
|
||||||
\end{tabular}
|
indicated by the dollar sign}
|
||||||
\end{center}
|
and Page 2 at \$4000.
|
||||||
|
Optionally 4 lines of text can be shown at the bottom of the
|
||||||
|
screen instead of graphics.
|
||||||
|
|
||||||
The hi-res graphics mode was a complex mess of NTSC hacks by Woz.
|
The lo-res mode is a bit easier to use.
|
||||||
You got 280x192 graphics, with 6 colors available. However the colors
|
It provides 40x48 blocks (40x40 if the four
|
||||||
were from NTSC artifacts and there were limitations on which colors
|
lines of text are displayed at the bottom).
|
||||||
could be next to each other (in blocks of 3.5 pixels) as well as
|
Fifteen colors are available (there are two greys which are indistinguishable).
|
||||||
fringing. Also the addresses were interleaved, so not a linear
|
Again the addresses are interleaved. Lo-res Page 1 is at \$400
|
||||||
framebuffer. Hi-res page0 is at
|
and Page 2 is at \$800.
|
||||||
\$2000\footnote{On 6502 systems hexadecimal values are
|
|
||||||
indicated by the dollar sign}
|
|
||||||
and page1 at \$4000.
|
|
||||||
Optionally 4 lines of text can be shown at the bottom of the
|
|
||||||
screen instead of graphics.
|
|
||||||
|
|
||||||
The lo-res mode is a bit easier to use. It is 40x48 blocks
|
Some amazing effects can be achieved by cycle counting, reading
|
||||||
(40x40 if 4 lines of text are displayed at the bottom).
|
the floating bus, and racing the beam while toggling graphics
|
||||||
15 colors are available, though there is fringing at the edges.
|
modes on the fly.
|
||||||
Again the addresses are interleaved. Lo-res page0 is at \$400
|
Unfortunately for you this demo does not do any of those things
|
||||||
and page1 is at \$800.
|
so you will not be reading about that today.
|
||||||
|
|
||||||
Some amazing effects can be achieved by cycle counting, reading
|
|
||||||
the floating bus, and racing the beam while toggling graphics
|
|
||||||
modes on the fly.
|
|
||||||
Unfortunately for you this demo does not do any of those things
|
|
||||||
so you will not be reading about that today.
|
|
||||||
|
|
||||||
%Later models added double low-res (80x48) and double hi-res (x y in
|
%Later models added double low-res (80x48) and double hi-res (x y in
|
||||||
%NTSC 15 color) but didn't appear until 198x, and only on later IIe, IIc
|
%NTSC 15 color) but didn't appear until 198x, and only on later IIe, IIc
|
||||||
@ -168,19 +184,20 @@ demos put this one to shame.
|
|||||||
%sadness of the users (Apple II forever).
|
%sadness of the users (Apple II forever).
|
||||||
|
|
||||||
|
|
||||||
\section{Setup Ramblings}
|
\section{Development Setup}
|
||||||
|
|
||||||
I do my development on Linux, using the nano text editor. I use the
|
I do all of my coding under Linux, using the nano text editor.
|
||||||
ca65 assembler from the cc65 project, which I find to be a reasonable
|
I use the ca65 assembler from the cc65 project, which I find to be a reasonable
|
||||||
tool although most ``real'' Apple II programmers look down on it for some
|
tool although many ``real'' Apple II programmers look down on it for some
|
||||||
reason.
|
reason.
|
||||||
|
I cross-compile the code, construct Apple DOS3.3 disk images using
|
||||||
|
custom tools I have written, and then do most testing in an emulator.
|
||||||
|
AppleWin (run under the wine emulator) is the easiest to use, but
|
||||||
|
MESS/MAME has cleaner sound.
|
||||||
|
|
||||||
I cross-compile on x86 Linux, construct Apple DOS33 disk images using
|
Once the code appears to work, I put it on a USB stick and transfer
|
||||||
some tools I've written, and then do most testing in an emulator.
|
to actual hardware using a CFFA3000 disk emulator installed in
|
||||||
(These days usually AppleWin under the wine emulator, or else MESS/MAME
|
the actual Apple II (an Apple IIe platinum edition).
|
||||||
which has cleaner sound output). Once things work then I'll stick things
|
|
||||||
on a USB stick and transfer to the CFFA3000 disk emulator installed in
|
|
||||||
the actual Apple II.
|
|
||||||
|
|
||||||
%\section{Related Work}
|
%\section{Related Work}
|
||||||
%
|
%
|
||||||
@ -197,137 +214,167 @@ the actual Apple II.
|
|||||||
|
|
||||||
\subsection{BOOTLOADER}
|
\subsection{BOOTLOADER}
|
||||||
|
|
||||||
An Applesoft BASIC "HELLO" program loads the binary.
|
An Applesoft BASIC ``HELLO'' program loads the binary automatically at bootup.
|
||||||
This just makes things auto-boot at startup, this doesn't count
|
This does not count towards the executable size, as you could manually BRUN
|
||||||
towards the executable size, you could manually BRUN the 8k program
|
the 8k program if you wanted.
|
||||||
if you wanted.
|
|
||||||
|
|
||||||
The binary is loaded at \$2000 (hi-res page0) and BASIC kicks into
|
To make the loading time slightly more interesting the binary is loaded at
|
||||||
HIRES mode before loading so you can watch as the memory is loaded
|
address \$2000 (hi-res page1) and BASIC is nice enough to enable
|
||||||
from disk in a seemingly random pattern.
|
graphics mode first so you can watch the display get filled with the random
|
||||||
|
pattern of the compressed image.
|
||||||
|
This entirely fills the 8k of the display, or would
|
||||||
|
if we POKEd the right address to turn off
|
||||||
|
the 4 lines of text on the bottom of the screen.
|
||||||
|
|
||||||
Since this is an 8k demo, the entirety of the program is shown on
|
Upon loading, execution starts at address \$2000
|
||||||
the screen (or would be if we POKEd the right address to turn off
|
|
||||||
the 4 lines of text on the bottom of the screen).
|
|
||||||
|
|
||||||
Execution starts at address \$2000
|
|
||||||
|
|
||||||
\subsection{DECOMPRESSER}
|
\subsection{DECOMPRESSER}
|
||||||
|
|
||||||
|
\begin{figure}[tb]
|
||||||
|
\begin{center}
|
||||||
|
\includegraphics[width=2in]{figures/hidden_vmw.png}
|
||||||
|
\end{center}
|
||||||
|
\caption{VMW logo hidden in the executable data.\label{fig:vmw}}
|
||||||
|
\end{figure}
|
||||||
|
|
||||||
The binary is LZ4 encoded. The decompresser flips to HGR page 1 so
|
The binary is encoded with the LZ4 algorithm.
|
||||||
we can watch memory as the program is decompressed.
|
We flip to hi-res Page 2 and decompress there so the user continues to get
|
||||||
|
a show of random noise.
|
||||||
|
|
||||||
The LZ4 decompression code was written by qkumba (Peter Ferrie).
|
The 6502 size-optimized LZ4 decompression code was written by qkumba
|
||||||
http://pferrie.host22.com/misc/appleii.htm
|
(Peter Ferrie).
|
||||||
|
% http://pferrie.host22.com/misc/appleii.htm
|
||||||
|
The program and data decompress to around 22k starting at \$4000.
|
||||||
|
It over-writes parts of DOS3.3, but since we will not be using the disk
|
||||||
|
any more this is not an issue.
|
||||||
|
|
||||||
The actual program/data decompresses to around 22k starting at \$4000.
|
If you look carefully at the upper left corner of the screen during
|
||||||
It over-writes parts of DOS3.3, but since we won't be using the disk
|
decompress you will see my triangular logo, which is supposed to evoke
|
||||||
anymore this isn't an issue.
|
my VMW initials (see Figure~\ref{fig:vmw}).
|
||||||
|
To do this I had to put the proper bit pattern at the interleaved
|
||||||
|
addresses of \$4000, \$4400, \$4800, and \$4C00.
|
||||||
|
This turned out to be way more trouble than it was worth.
|
||||||
|
As an interesting note, the image data at \$4000 is executed as it maps
|
||||||
|
to (mostly) harmless code.
|
||||||
|
|
||||||
At the top left corner of the screen you'll see the VMW triangles logo
|
The demo was optimized to fit in 8k, and this is difficult when your program
|
||||||
as it decompresses. To do this I had to put the proper bit pattern
|
is compressed.
|
||||||
at \$4000, \$4400, \$4800, and \$4C00. I mean to have some words too
|
Removing instructions sometimes makes the binary {\em larger} as it no longer
|
||||||
but ran out of disk space. The bit pattern at \$4000 is executable
|
compresses as well.
|
||||||
and is run as code.
|
Long runs of values (such as 0 padding) are essentially free.
|
||||||
|
This mostly turned into an exercise of guess-and-check until everything fit.
|
||||||
Optimizing for code size inside of a compressed binary is a pain.
|
|
||||||
Removing instructions sometimes made the binary larger as it no longer
|
|
||||||
compressed as well. Long runs of values (such as 0 padding) are
|
|
||||||
essentially free. This was a difficult challenge.
|
|
||||||
|
|
||||||
\subsection{FADE EFFECT}
|
\subsection{FADE EFFECT}
|
||||||
|
|
||||||
The title screen fades in from black.
|
The title screen fades in from black.
|
||||||
|
|
||||||
This is a software hack, with a lookup table copying from an off-screen
|
This is a software hack as the Apple II does not have palette support.
|
||||||
buffer. The Apple II doesn't have any palette support.
|
The image is loaded to an off-screen buffer and a lookup table is used to
|
||||||
|
copy in the faded versions on the fly.
|
||||||
|
|
||||||
\subsection{TITLE SCREEN}
|
\subsection{TITLE SCREEN}
|
||||||
|
|
||||||
Once things are decompressed, we jump to \$4000. We switch to low-res
|
\begin{figure}[tb]
|
||||||
mode for the rest of the DEMO.
|
\begin{center}
|
||||||
|
\includegraphics[width=\columnwidth]{figures/mode7_demo_title.png}
|
||||||
|
\end{center}
|
||||||
|
\caption{The title screen.\label{fig:title}}
|
||||||
|
\end{figure}
|
||||||
|
|
||||||
A background image is loaded from disk. This is RLE encoded (probably
|
Once decompression is done, execution continues at address \$4000.
|
||||||
unnecessary when being further LZ4 encoded).
|
We switch to low-res mode for the rest of the demo.
|
||||||
|
|
||||||
Why not just load the program at \$400 and load the graphics image for
|
A title screen is loaded, as seen in Figure~\ref{fig:title}.
|
||||||
free? Well, remember the graphics are 40x48 (shared with the text).
|
The image is run-length encoded (RLE) which is
|
||||||
Really it's 40x24, with each text char mapping to 4-bits top/bottom
|
probably unnecessary when being further LZ4 encoded.
|
||||||
for color. Do the math, we have 1k reserved for this mode but 40x24
|
(The LZ4 compression was a late addition to this endeavor).
|
||||||
is only 960 bytes. It turns out there are "holes" in the address range
|
|
||||||
that aren't displayed, and various pieces of hardware use these holes
|
|
||||||
as scratchpad memory. So if you just blindly uncompress graphics data
|
|
||||||
there you can corrupt the scratchpad. So you have to be careful
|
|
||||||
when uncompressing to skip the holes.
|
|
||||||
|
|
||||||
The title screen has scrolling text at the bottom. This is nothing fancy,
|
Why not save some space and just load our demo at \$400 and negate the need
|
||||||
the text is in a buffer off screen and a 40x4 chunk of RAM is copied in
|
to copy the image in place?
|
||||||
every so many cycles.
|
Remember the graphics are 40x48 (shared with the text display region).
|
||||||
|
It might be easier to think of it as 40x24 characters, with the top / bottom
|
||||||
|
4-bits of each ASCII character being interpreted as colors for a half-height
|
||||||
|
block.
|
||||||
|
If you do the math you will find this takes 960 bytes of space, but the memory
|
||||||
|
map reserves 1k for this mode.
|
||||||
|
There are ``holes'' in the address range that are not displayed, and
|
||||||
|
various pieces of hardware can use these as scratchpad memory.
|
||||||
|
This means just overwriting the whole 1k with data might not work out well
|
||||||
|
unless you know what you are doing.
|
||||||
|
To this end the RLE decompression code skips the holes just to be safe.
|
||||||
|
|
||||||
You might notice that there is tearing/jitter in the scrolling, even
|
The title screen has scrolling text at the bottom.
|
||||||
though we are double-buffering the graphics. This is because there is
|
This is nothing fancy, the text is in a buffer off screen and a 40x4
|
||||||
not a reliable cross-platform way to get the VBLANK info (especially
|
chunk of RAM is copied in every so many cycles.
|
||||||
on older machines) so we are having some bad luck about when we flip
|
You might notice that there is tearing/jitter in the scrolling even
|
||||||
pages.
|
though we are double-buffering the graphics.
|
||||||
|
Sadly there is not a reliable cross-platform way to get the VBLANK info
|
||||||
|
on Apple II machines, especially the older models.
|
||||||
|
This is even more noticeable in the recorded video, as the capture card and
|
||||||
|
movie encoding conspire to make this look worse than things look in person.
|
||||||
|
|
||||||
\subsection{MOCKINGBOARD MUSIC}
|
\subsection{MOCKINGBOARD MUSIC}
|
||||||
|
|
||||||
I like chiptune music, especially that for AY-3-8910 based systems.
|
No demo is complete without some exciting background music.
|
||||||
Before obtaining a Mockingboard I built a Raspberry Pi chiptune player
|
I like chiptune music, especially the kind you can find that is made
|
||||||
that is essentially the same hardware.
|
for AY-3-8910 based systems.
|
||||||
|
I gained some expertise during the long wait for my Mockingboard to arrive
|
||||||
|
by building a Raspberry Pi chiptune player that is essentially the same
|
||||||
|
hardware.
|
||||||
|
|
||||||
Most of my sound infrastructure involves YM5 files, which are often used
|
The song being played is a stripped down and re-arranged version of
|
||||||
by ZX Spectrum and ATARI ST users. These are usually register dumps
|
``Electric Wave'' from CC'00 by EA (Ilya Abrosimov).
|
||||||
taken typically at 50Hz. So to play them back you just have to interrupt
|
|
||||||
50 times a second and write the registers.
|
|
||||||
|
|
||||||
To program the Mockingboard, each AY-3-8910 chip has 14 sound related
|
Most of my sound infrastructure involves YM5 files, a format commonly
|
||||||
registers that control the 3 channels. Each AY chip has a dedicated
|
used by ZX Spectrum and ATARI ST users.
|
||||||
VIA 6522 parallel I/O chip that handles the I/O.
|
These are essentially just AY-3-8910 register dumps taken at 50Hz.
|
||||||
|
To play these back just set up the sound card to interrupt 50 times a second
|
||||||
|
and then write out the 14 register values from that frame.
|
||||||
|
|
||||||
Doing this quickly enough is a challenge on the Apple II. For each
|
% To program the Mockingboard, each AY-3-8910 chip has 14 sound related
|
||||||
register you have to do a handshake, set the register \# and the value.
|
% registers that control the 3 channels. Each AY chip has a dedicated
|
||||||
This can take upwards of 40 1MHz cycles per register.
|
% VIA 6522 parallel I/O chip that handles the I/O.
|
||||||
|
|
||||||
For complex chiptune files (especially those written on an ST with much
|
Writing out the registers quickly enough is a challenge on the Apple II.
|
||||||
faster hardware) it's sometimes not possible to get exact playback
|
For each register you have to do a handshake then set both the register
|
||||||
due to the delay. Also one AY is on the left channel and one on the right
|
number and the value.
|
||||||
so you have to write both if you want sound from both speakers.
|
It is hard to do this in less than forty 1MHz cycles for each register.
|
||||||
|
With complex chiptune files (especially those written on an ST with much
|
||||||
|
faster hardware) it is sometimes not possible to get exact playback
|
||||||
|
due to the delay.
|
||||||
|
Further slowdown happens as you want to write both AY chips (the output
|
||||||
|
is stereo, with one AY on the left and one on the right).
|
||||||
|
|
||||||
I have a whole suite of code for manipulating YM sound data, in my
|
% I have a whole suite of code for manipulating YM sound data, in my
|
||||||
vmw-meter git repository.
|
% vmw-meter git repository.
|
||||||
|
|
||||||
The first step for getting this to work is detecting if a mockingboard is
|
Our code detects a Mockingboard at startup, we are lazy and only support
|
||||||
there. This can be in any slot 1-7 on the Apple II, though typically
|
finding the card in Slot 4 (which is a fairly typically location).
|
||||||
Slot 4 is standard (in this demo we only check slot 4).
|
% The first step for getting this to work is detecting if a Mockingboard is
|
||||||
|
%% there. This can be in any slot 1-7 on the Apple II, though typically
|
||||||
The board is initialized, and then one of the 6522 timers is set to
|
% Slot 4 is standard (in this demo we only check slot 4).
|
||||||
interrupt at 25Hz (it has to be an on-board timer as the default
|
The board is initialized, and then one of the 6522 timers is set to
|
||||||
Apple II has no timers).
|
interrupt at 25Hz.
|
||||||
|
% (it has to be an on-board timer as the default
|
||||||
Why 25Hz and not 50Hz? At 50Hz with 14 registers you use 700 bytes/s.
|
% Apple II has no timers).
|
||||||
So a 2 minute song would take 84k of RAM, much more than is available.
|
Why 25Hz and not 50Hz? At 50Hz with 14 registers you use 700 bytes/s.
|
||||||
|
So a 2 minute song would take 84k of RAM, much more than is available.
|
||||||
For this demo I run at 25Hz, and also pack the 14 registers of the data
|
To allow the song to fit in memory (without the fancy circular buffer
|
||||||
into 11 (there are various fields that are not packed well, we can
|
decompression utilized in my Chiptune Player Music Disk demo) we have
|
||||||
unpack at play time). Also I stripped out the envelope data as many
|
to reduce the size significantly.
|
||||||
songs do not use it (so this is a lossy compression method).
|
First we reduce the music to only need to be updated at 25Hz.
|
||||||
|
We reduce the register data from 14 bytes to 11 bytes by stripping off
|
||||||
Also, we keep track of the last values written last frame and only
|
the envelope effects and packing together some of the fields that have
|
||||||
write out to the board if things change, which helps with the latency
|
unused bits.
|
||||||
a bit.
|
To help with latency on playback we keep track of the last frame written
|
||||||
|
and only write to the registers that have changed.
|
||||||
The sound quality suffered a bit, but it's hard to fit a catchy chiptune
|
|
||||||
file in 8K.
|
|
||||||
|
|
||||||
The song being played is a stripped down and re-arranged version of
|
|
||||||
"Electric Wave" from CC'00 by EA (Ilya Abrosimov).
|
|
||||||
|
|
||||||
|
In the end the sound quality suffered a bit, but we were able to fit an
|
||||||
|
acceptably catchy chiptune inside of our 8k payload.
|
||||||
|
|
||||||
\subsection{MODE7 BACKGROUND}
|
\subsection{MODE7 BACKGROUND}
|
||||||
|
|
||||||
"MODE7" was a Super Nintendo (SNES) graphics mode that took a tiled
|
``MODE7'' is a Super Nintendo (SNES) graphics mode that took a tiled
|
||||||
background and transformed it to look as if it was squashed out to
|
background and transformed it to look as if it was squashed out to
|
||||||
the horizon, giving a 3d look. The SNES did this in hardware, but
|
the horizon, giving a 3d look. The SNES did this in hardware, but
|
||||||
in this demo we do this in software.
|
in this demo we do this in software.
|
||||||
@ -371,6 +418,14 @@ the actual Apple II.
|
|||||||
|
|
||||||
\subsection{BOUNCING BALL ON CHECKERBOARD}
|
\subsection{BOUNCING BALL ON CHECKERBOARD}
|
||||||
|
|
||||||
|
\begin{figure}
|
||||||
|
\begin{center}
|
||||||
|
\includegraphics[width=\columnwidth]{figures/m7_screen1.jpg}
|
||||||
|
\caption{Bouncing ball on infinite checkerboard.\label{fig:ball}}
|
||||||
|
\end{center}
|
||||||
|
\end{figure}
|
||||||
|
|
||||||
|
|
||||||
What would a demo be without some sort of bouncing geometric shape.
|
What would a demo be without some sort of bouncing geometric shape.
|
||||||
|
|
||||||
This is just done with 16 sprites. The sphere was modeled in OpenGL
|
This is just done with 16 sprites. The sphere was modeled in OpenGL
|
||||||
@ -381,10 +436,17 @@ the actual Apple II.
|
|||||||
|
|
||||||
The clicking noise on bounce is just touching the speaker at \$C030.
|
The clicking noise on bounce is just touching the speaker at \$C030.
|
||||||
It's mostly there to give some sound effects for those playing the demo
|
It's mostly there to give some sound effects for those playing the demo
|
||||||
without a mockingboard.
|
without a Mockingboard.
|
||||||
|
|
||||||
\subsection{TFV SPACESHIP FLYING}
|
\subsection{TFV SPACESHIP FLYING}
|
||||||
|
|
||||||
|
\begin{figure}[tb]
|
||||||
|
\begin{center}
|
||||||
|
\includegraphics[width=\columnwidth]{figures/m7_screen4.jpg}
|
||||||
|
\end{center}
|
||||||
|
\caption{Spaceship flying over an island.\label{fig:tb1}}
|
||||||
|
\end{figure}
|
||||||
|
|
||||||
The spaceship, water splash, and shadows are all sprites. This is all
|
The spaceship, water splash, and shadows are all sprites. This is all
|
||||||
done in software, the Apple II has no sprite hardware.
|
done in software, the Apple II has no sprite hardware.
|
||||||
|
|
||||||
@ -394,6 +456,14 @@ the actual Apple II.
|
|||||||
|
|
||||||
\subsection{STARFIELD}
|
\subsection{STARFIELD}
|
||||||
|
|
||||||
|
\begin{figure}[tb]
|
||||||
|
\begin{center}
|
||||||
|
\includegraphics[width=\columnwidth]{figures/m7_screen3.jpg}
|
||||||
|
\end{center}
|
||||||
|
\caption{Spaceship with starfield.\label{fig:stars}}
|
||||||
|
\end{figure}
|
||||||
|
|
||||||
|
|
||||||
The starfield is your typical starfield code. Only 16 stars are modeled.
|
The starfield is your typical starfield code. Only 16 stars are modeled.
|
||||||
It re-uses the fast-multiply code from the mode7 graphics.
|
It re-uses the fast-multiply code from the mode7 graphics.
|
||||||
|
|
||||||
@ -413,6 +483,14 @@ the actual Apple II.
|
|||||||
|
|
||||||
\subsection{RASTERBARS/CREDITS}
|
\subsection{RASTERBARS/CREDITS}
|
||||||
|
|
||||||
|
\begin{figure}[tb]
|
||||||
|
\begin{center}
|
||||||
|
\includegraphics[width=\columnwidth]{figures/m7_screen2.jpg}
|
||||||
|
\end{center}
|
||||||
|
\caption{Rasterbars, stars, and credits.\label{fig:credits}}
|
||||||
|
\end{figure}
|
||||||
|
|
||||||
|
|
||||||
The credits happen with the starfield continuing to run.
|
The credits happen with the starfield continuing to run.
|
||||||
|
|
||||||
The text is written in the bottom 4 lines of the screen. Some inverse-mode
|
The text is written in the bottom 4 lines of the screen. Some inverse-mode
|
||||||
@ -443,63 +521,44 @@ More details, disk image, and full source can be found at the website:
|
|||||||
\url{http://www.deater.net/weave/vmwprod/mode7_demo/}
|
\url{http://www.deater.net/weave/vmwprod/mode7_demo/}
|
||||||
|
|
||||||
\begin{table}
|
\begin{table}
|
||||||
|
\begin{center}
|
||||||
\begin{verbatim}
|
\begin{verbatim}
|
||||||
|
|
||||||
-------- $ffff
|
------------- $ffff
|
||||||
| ROM/IO |
|
| ROM/IO |
|
||||||
-------- $c000
|
------------- $c000
|
||||||
| | 32k decompress
|
| |
|
||||||
-------- $4000
|
| Uncompressed|
|
||||||
| load | 8k
|
| Code/Data |
|
||||||
-------- $2000
|
| |
|
||||||
|
------------- $4000
|
||||||
|
| Compressed |
|
||||||
|
| Code |
|
||||||
|
------------- $2000
|
||||||
| free |
|
| free |
|
||||||
-------- $1c00
|
------------- $1c00
|
||||||
| Scroll |
|
| Scroll |
|
||||||
| Data |
|
| Data |
|
||||||
-------- $1800
|
------------- $1800
|
||||||
|Multiply|
|
| Multiply |
|
||||||
| Tables |
|
| Tables |
|
||||||
-------- $1000
|
------------- $1000
|
||||||
|GR pg 2 | 1k
|
| LORES pg 3 |
|
||||||
|-------- $0c00
|
------------- $0c00
|
||||||
|GR pg 1 | 1k
|
| LORES pg 2 |
|
||||||
|-------- $0800
|
------------- $0800
|
||||||
|GR pg 0 | 1k
|
| LORES pg 1 |
|
||||||
-------- $0400
|
------------- $0400
|
||||||
| | 0.5
|
|free/vectors |
|
||||||
-------- $0200
|
------------- $0200
|
||||||
| stack | 0.25
|
| stack |
|
||||||
-------- $0100
|
------------- $0100
|
||||||
|zero pg | 0.25
|
| zero pg |
|
||||||
------- $0000
|
------------- $0000
|
||||||
|
|
||||||
\end{verbatim}
|
\end{verbatim}
|
||||||
|
\end{center}
|
||||||
\caption{Memory Map (not to scale)}
|
\caption{Memory Map (not to scale)}
|
||||||
\end{table}
|
\end{table}
|
||||||
|
|
||||||
\begin{figure}
|
|
||||||
\includegraphics[width=\columnwidth]{figures/hidden_vmw.png}
|
|
||||||
\caption{Blah}
|
|
||||||
\end{figure}
|
|
||||||
|
|
||||||
\begin{figure}
|
|
||||||
\includegraphics[width=\columnwidth]{figures/m7_screen2.jpg}
|
|
||||||
\end{figure}
|
|
||||||
|
|
||||||
\begin{figure}
|
|
||||||
\includegraphics[width=\columnwidth]{figures/m7_screen4.jpg}
|
|
||||||
\end{figure}
|
|
||||||
|
|
||||||
\begin{figure}
|
|
||||||
\includegraphics[width=\columnwidth]{figures/m7_screen1.jpg}
|
|
||||||
\end{figure}
|
|
||||||
|
|
||||||
\begin{figure}
|
|
||||||
\includegraphics[width=\columnwidth]{figures/m7_screen3.jpg}
|
|
||||||
\end{figure}
|
|
||||||
|
|
||||||
\begin{figure}
|
|
||||||
\includegraphics[width=\columnwidth]{figures/mode7_demo_title.png}
|
|
||||||
\end{figure}
|
|
||||||
|
|
||||||
\end{document}
|
\end{document}
|
||||||
|
Loading…
Reference in New Issue
Block a user