Avoid Spikes

And so it begins...

2010-08-26T20:18:00.000-04:00

..the Great Garage Cleanout of 2010 that is.

Well, I have to make room, so the arcade games are starting to go. Gremlin "Comotion" and Midway "Extra Bases" were parted out today. The dead husks are sitting out at the curb as I type. I kept the PCB's and took some last photos which I'll add a little later.

These were both used to develop the MAME drivers. I created "blockade.c" based on Comotion and some schematics from Al Kossow. The Midway "Extra Bases" cocktail contained a Black and White monitor, which was interesting because the game at that time was in color in MAME. It turns out that the game had a dip switch, which could either drive a Black and White monitor directly with the Luminance output, or in another configuration, drive the color conversion board and play the game in color. This was sort of "unknown" or at least not well known at the time in the MAME circles.

Ironically, as I pulled the monitor out of the "Extra Bases", I noticed it had some burn-in from "Blockade", which is basically the same hardware as "Comotion". (Obviously not the original monitor)

These two games were bought from two different places, but being of similar vintage I guess I shouldn't be surprised.

Vintage Gaming Party @ Penguicon

2010-04-16T12:10:00.000-04:00

I am planning to have a hotel room party at Penguicon this year, bringing my old game consoles out of storage. (Actually two parties, one on Friday and one on Saturday, if all goes well.)

I started by testing out a Coleco "Telstar" Pong and the Atari 2600 yesterday. You can see my team of playtesters trying out some "big-screen" Pong action here:

Here is just a taste of the excitement in store... :) Next I'll be pulling out the Intellivision, Vectrex, and whatever else I can dig up. If anyone has some smallish TV's (preferable analog!) they want to loan for the weekend, I could probably use them.

Perhaps I'll throw in some Apple II games, or some other system emulators. Moria/Angband? Text Adventures? Trek? Am I crazy enough to bring in a full-sized arcade game? The possibilities are endless, but the hotel room is not, unfortunately. If only I had a TARDIS...

The Mathematics of Calendar Reform

2010-04-03T00:29:00.001-04:00

The Gregorian Calendar is inconsistent, and there is only so much we can do about it. The earth takes about 365.24 days to go around the sun. The number of days in the year are nicely controlled with leap years and leap seconds, to make this work out.

We have a tradition of the 7-day week. We have a tradition of months which are 28 or 30 or 31 days long. But worst of all, each year starts on a different day of the week, forcing us all to have new calendars each year.

So, can we do better? Sure we can. Let's look at the numbers:

First, every number can be expressed as a series of primes multiplied together, called a "prime factorization".

365 = 5*73

Yuck. Well, if we want 5 seasons of 73 days each, we are all set. I don't think so :)

364 = 2*2*7*13

This has potential. We could have 7 day weeks, 4 weeks in a month, and 13 months. Plus one day every year which is outside the "days of the week". A kind of yearly holiday for the 365th day. And on leap years, we need one more day like this. Then, every year would have the same pattern. Indeed, these kinds of 13-month systems have been proposed, and even used occasionally. The most recent version is probably this one:

http://en.wikipedia.org/wiki/International_Fixed_Calendar

I admit they are probably the most elegant, but I think the world will not readily switch to 13-month calendars.

So, we have two other choices. Give up months altogether, and go with 7*13 = 91 day quarters. This has also been proposed:

http://en.wikipedia.org/wiki/World_Season_Calendar

The other choice is to stick with three months in a quarter, with one month getting 31 days and the other 2 getting 30 days. I tend to think this is the most reasonable course of action. Here is a calendar system that works this way:

http://en.wikipedia.org/wiki/World_Calendar

Now, so others have proposed that, instead of having a day or two each year outside of the week, we should stick with 7-day weeks all year, but change the number of weeks per year to keep the calendar with the right "average days per year". These so-called "leap-week" calendars are interesting, but I think they would tend to drift a little too far from the astronomical events for my tastes. The first day of each season would drift around by a few days each year.

Anyways, for more info on this subject, look up "Calendar Reform"

Two good sources are wikipedia:
http://en.wikipedia.org/wiki/Calendar_reform
and this one:
http://personal.ecu.edu/mccartyr/calendar-reform.html

I'm in favor of The World Calendar, how about you?

Blockbuster 'n4 - by Elcon Industries

2010-03-20T22:54:00.012-04:00

I'm going to be getting rid of some of my videogames. They take up too much space, and I'm never going to get around to repairing them all. This one is from a company called Elcon Industries, formerly of Royal Oak, MI. It is a discrete logic game (I assume), with 5 different games available. (The marquee actually says "Blockbuster +4", which makes more sense.)

I assume these are all variations on Pong/Breakout/etc. As you can see, it's not working properly, but it does run through the "attract mode" on power up.

I'm wondering if this is an original game, or a clone of an existing one?

You can see some graphics glitches, but it is kind of interesting. The Cosmic Attackers game I have from the same company had a Sega Space Attack PCB inside.

Here are some more stills:

You can see that it also has a few bulbs which light up some game description text, and there is also a single "seven-segment"-style display for good measure. I'm not sure what that is for.

I'd love to hear from you if you have any info on this game, or others like it, or info on Elcon Industries, or ideas on what to do next :)

I don't have the key to the back of the cab, and I haven't "broken into" the back to take a look at the circuit board yet. I think that might be the next step.

Math problem #1 - piecewise approximating functions

2010-02-06T22:13:00.006-05:00

I'm the kind of person that can get very interested in things that others might not notice. For me, his seems to occur from time to time with math problems. I'll be thinking about an engineering problem, and I will get caught up with some mathematical aspect of it. Usually, it's some problem which is easy to state but not obvious to solve. (Then again, I'm not a mathematician)

Over the years, I've gathered up a list of these problems. And now, I'd like to share some of them on this blog. I hope some of you, at least, will find them as interesting as I do.

---

Today's problem is fairly simple to state - and I thought about it for the first time many years ago. Suppose I have a continuous function y=f(x), defined on an interval from x0 to xn. I know _everything_ there is to know about the function. Now, for some reason, I need to approximate the function using a "piecewise-linear" function. This is just a set of straight lines connected together at "break" points. (You can also think of this as an approximation based on splines.)

For say, a fixed number of break points, what is the "best" way to approximate the function? (BTW - this is something that is practically done all the time, in embedded computer programs, using "table lookups" to approximate functions)

Some clues:

For a given set of breakpoints located at each x_i, you can start by picking the breakpoints at (x_i, f(x_i)). In other words, points on the curve f(x), and connecting the points with straight lines. However, you will quickly notice that the approximation is biased, based on the concavity of the curve.

A better way for a given set of points at x_i, is to solve the linear least-squares problem to find the optimal y values, which minimize the error between the approximate curve and the actual one.

But the key question seems to be - how do I locate my points in x? I see no easy way to do this, without non-linear iteration. It seems strange that it is trivial to locate the points in Y given X values, but hard to locate the X values. I can imagine some heuristic rules like "I should use more breakpoints where the function is 'curvier'". But it's not at all clear what this means :) Maybe I need to think about the meaning of "best" a bit more.

So, to summarize, we have a situation where we have a function which we know everything about, and a simple space of approximating functions, but we seem unable to match the two together, without resorting to nonlinear iteration.

If this one is too easy for you, feel free to handle extensions to this problem with higher order piecewise splines, and/or multidimensional functions. :) I can imagine practical applications for a good algorithm in this area.

Yikes - more than 2 years without blogging!

2008-08-14T15:26:00.003-04:00

Not the kind of anniversary I wanted to celebrate. Anyways, I'm in the middle of a move to a new house, and work is heating up. So, hopefully around October, things will settle down...and I will try to post something more regularly.

The Road to Reality

2006-05-08T09:48:00.000-04:00

I have been interesting in Physics as a hobby for a very long time. Back in the mid-90's, I was reading about Quantum Mechanics and Relativity on a fairly regular basis. I had to really dig to find books that were deeper than a purely "popular" treatment, but not so deep that an engineer could actually make sense of them. Some math, not all math.

Having been trained as an engineer is "almost enough" to handle "some" of the math, but I ended up with an awfully long road ahead. I eventually got a bit discouraged, but never quite gave up. (Emulation came along and I got a bit distracted for a number of years.)

In 2004 Roger Penrose wrote a giant book on Math and Physics, call "The Road to Reality: A Complete Guide to the Universe". It is a highly mathematical, modern treatment, but it builds on itself such that, theoretically, someone with some math background can actually understand it all. (At least, they'll be able to self-direct to other resources as needed.) There are 16 chapters of Math (the first 1/3 or so), followed by as many on Physics. For comparison, my formal math training ended at chapter 7. I now find myself in chapter 15, nearly finished with the math section. It is definitely not for everyone, but it's exactly what I needed.

Finally, I have found that discussing the details of the book can help a lot with the understanding. I recently created a Yahoo Group called RTRFANS, for just this purpose. With this book, and with internet resources that weren't available in the mid-90's, I've now got a shot at understanding truly modern physics.

Some porting work

2006-05-08T09:35:00.000-04:00

I really need to post more often!

For a while now, I've been wanting to experiment with new methods of high-speed circuit simulation. The idea would be to prototype some discrete-audio stuff, possibly for MAME, using something like Python.

After looking into the requirements, I realized that I needed to handle polynomials with a single variable, and ratios of these polynomials. Also, I needed to be able to handle real or complex variables. I looked around on the web, and I found that SciPy is finally coming along nicely on Windows. However, I wasn't entirely happy with the root finder they use.

Along the way, I also found the ratfun package, which looked perfect, but was unsupported on Windows. I dug in and in a couple weekends, got it building under Windows. I think I'll be using it for the experiments, whenever I get back to it.

The Joy of LaTeX

2006-02-07T14:37:00.000-05:00

Ok, I'm a geek. Over the past 10 years or so, I've worked on a handful of math and engineering problems that I thought were interesting. Yes, most of them were "spare-time" activities, although a few were inspired by work stuff. I recently made a list of all of them, and I suddenly had the urge to publish them. Maybe some other people will find these things interesting as well.

At any rate, I wanted a way to publish them with all the math equations, as well as generate PDF's and HTML. I had heard about LaTeX for a long time, but now I had a fine excuse to give it a try.

I first tried the TeXLive distribution, but I never could get it to work on Windows. (Maybe this has been fixed since then) Then I tried MikTeX. It was a fairly straightforward installation. After working out a few examples, I was hooked. My first draft of a test article turned out pretty well:

http://www.avoidspikes.com/textest/gamma.html

I use pdflatex to generate pdfs and htlatex (part of tex4ht) to create html + pngs.

At any rate, it's nice to see that free software can be used to do professional typesetting. I'm planning to use this stuff to document my math problems, as well as some theory behind discrete sound filtering in MAME.

Actual MAME-related work!

2006-01-10T12:10:00.000-05:00

For those who haven't heard, the speech chip used in Berzerk has been reverse-engineered by "Lord Nightmare"! This is something I've been waiting for for about 7-8 years! I'm sure that the emulation will end up in MAME and PinMAME sooner or later.

Because of this, I spent some time over Christmas looking at the analog filters on the Berzerk speech board. (These are applied to the sound after it comes out of the chip.) I finished the analysis, and it should be pretty straightforward to add them into MAME after the chip emulation is done.

For what it's worth, I've been trying out Maxima with wxMaxima to do the symbolic math for circuit analysis. I know, I could have used SPICE or something - but doing the math from scratch makes it easier to understand what is going on.

After I worked out about half of the math for these filters by hand, I ended up with about 6 pages of algebra. At this point, I figured I should use this as an excuse for learning Maxima. Sure enough, I found an error on page 5. Darned minus signs! :)

The second half of the analysis took about 5 minutes, since the code from the first half was already done, and I could re-use it!

For those who care - the filter is a third-order lowpass - a first order lowpass, followed by a second order with a resonant peak around 2400 Hz.

Firefly and Serenity

2005-10-10T10:01:00.000-04:00

Well, I did it. I managed to watch all the Firefly episodes before checking out the movie, with two hours to spare :)

I've got to say, with every episode I watched, I enjoyed the series more. The writing and character development is really well done, and it's pretty darned funny to boot. I can't believe they canceled it just as it was taking off. It was kind of the opposite of what Star Trek and Star Wars have been of late. Less tech, and much more fun. And this is from a guy who has a penchant for hard science fiction.

At any rate, I also enjoyed the film. I went with three others who hadn't seen Firefly, and they seemed to like it as well. I think it's quite a tough job to introduce this world and so many characters to an audience who may never have seen the series. Still the movie seems to do all this and more, with entertainment value that is missing in many other sci-fi films of late.

However, I actually think this whole concept works better as a TV series, rather than a series of movies. So, now I join the ranks who are hoping someone will bring back the TV show in some incarnation.

More non-emulation news :)

2005-10-03T12:31:00.000-04:00

I have still been up to my neck in "real work". I hope it will slowdown in the next month or so. When I do get a few minutes - I am trying to read, and maybe catch up on TV a little.

I'm carving out enough time to finish Neal Stephenson's "Baroque Cycle." I find these books to be amazing. Exciting, intellectually challenging, but very rewarding. I feel like I've actually visited the late 17th and early 18th century. And Neal's themes about science, technology, commerce, etc. are quite intriguing.

As I side note, I TiVo'd the whole "Firefly" series, which I'd like to watch before I go see "Serenity". I haven't heard anything but good things about the movie.

I'm still here...!

2005-08-11T12:31:00.000-04:00

Ok, I haven't done much on MAME at all, except that I bought a Zero Hour board on eBay. Hopefully I can improve the driver when I finally get time to work on MAME again, now that I'm intimately familiar with the starfield generator circuit. :)

I've been extremely busy with work and home life. One weekend, I built a giant play system for my kids. A lot of work, but it turned out pretty nice!

Finally, for those who visit my horribly outdated web pages at dsplib.com, - I'm giving up the domain. You can still reach those pages here, until I move them again. Pay no attention to the inactive blog pages there :)

MAME Quickies

2005-06-15T10:02:00.000-04:00

I've submitted 2 updates to MAME in the last 3 days. The first is the much improved Space Raider. The second one hooked up the starfield generator code to Zero Hour and Red Clash. I'm still planning to write up something bigger on this - describing how it all works - but I've been too busy this week.

Space Raider Stars - done

2005-06-12T02:08:00.000-04:00

Just a quick note to say that I've got the graphics on Space Raider 100% correct, including the starfield behavior. I've still got a couple things to look at, but my plan is to submit a driver update tommorrow. I'll try to add some screenshots a that time as well.

Speed Coin

2005-05-25T11:53:00.001-04:00

I've had almost no time to finish Space Raider lately, so I thought I'd talk about the history of a game I own - Speed Coin.

As far as I know, I'm the only one with a Speed Coin cabinet. It's definitely a prototype, as the cabinet is made of nice plywood and not particle board. Also, the marquee and control panel are made of colored paper, colored electrical tape, and a blown-up xerox copy of a coin face. My understanding is that it came from Stern when it shut down.

The boardset is a Scramble, with hand-labelled ROM chips inside. Also, the wiring harness is different, since it only requires a 2-way joystick.

When I went to plug this into the Scramble driver in MAME (back in 1999!), I was stymied by the fact that the background was blue in MAME, but black on the "real thing". I traced through the PCB only to find that the monitor was adjusted with the blue gun turned off! When I adjusted it, it matched MAME exactly.

In case you are wondering about the sound, the music sounds kind of muted and noisy on the real thing, just like in MAME.

Last year, I was stunned to play Speed Coin in an arcade in Nashville, Tennessee. It turns out the Ultracade guys added that game to their Multigame system, under "Arcade Classics"?!. I'm sure they used the ROM images I dumped in my basement, and here it was on a machine in another city. Pretty strange feeling.

I really don't think it's a classic. More like "Arcade Relics". :)

Oh well, I'll get back to Space Raider this weekend, hopefully. I have a newly-found JAMMA harness and a brand new RGB-to-TV adapter which should make things easier. With that, I'll be able to take screenshots from actual boards, and compare them with MAME.

Space Raider Stars

2005-05-03T12:33:00.000-04:00

Well, I found time to make a few more discoveries. The Space Raider boardset is 3 PCB's. Two of them are full size and obviously two halves of the same design. Then, there is a little PCB grafted on top, connected via a 24-pin dip connector, with wires going to the other two boards.

I suspected that this board was the starfield generator. Sure enough, if you unplug it and run the board, the stars disappear. Cool - less work for me.

Then, I noticed something else. Two chips were missing from the board, and it was labeled with the number 8011, unlike the other boards. Maybe this board is from another game? Searching through the MAME code, there is a comment that Universal game #8011 is Zero Hour.

Luckily, a manual and schematics are available for Zero Hour. The starfield board is the same! In Zero Hour, this board provides both color generation and stars. The missing chips in Space Raider disable the color generation part, since that's already on the main board.

Anyways, I added preliminary support for the scrolling stars to MAME, and it looks right. I need to measure a few more things to get the timing exact. When I'm done with Space Raider, I'd like to add the stars to the Zero Hour / Red Clash driver, since it's missing there as well.

As a side note - I hope these posts are interesting to someone. I think it's kinda cool to document the little things that it takes to get a MAME driver right.

Space Raider - update

2005-04-20T12:19:00.000-04:00

Last night I got a bit further. I fixed up the cocktail mode, and decoded all the dip switches except one. I also found and decoded the bits which control the scroll speed and direction of the starfield. Finally, I found a "hidden" test mode while disassembling some of the code. (Hold down the fire button while resetting the game.) The todo list is getting shorter...!

Space Raider graphics fixes

2005-04-17T22:36:00.000-04:00

I got my JAMMA cabinet running again, built the Space Raider-to-JAMMA adapter, and got the board up and running over the weekend. This allowed me to fix most of the graphics problems with the driver! (Most notably, the grid is animating properly now, and it's the right color.)

The only thing that's noticable now is the lack of a background starfield. Without schematics, this will probably take a long time to get right.

Atom syndication and blogger formatting

2005-04-10T16:45:00.000-04:00

I'm not sure why my paragraph breaks are only showing up "sometimes" in the atom syndication of this blog. If someone has a clue, I'd love to hear it. I think it might have to do with whether I'm editing in HTML mode or not. Oh well, what do I expect for free... :)

The Car of the Future

2005-04-10T16:09:00.000-04:00

This weekend, I had the pleasure of test-driving a 2005 Toyota Prius.

For those who don't know, this is a hybrid vehicle built from the ground up by Toyota. The engineering that has gone into this car is amazing. It has an internal combustion engine, and 2 electric motor/generators. They are connected to the wheels by an innovative planetary gear arrangement, which is basically simpler than an automatic transmission, yet has all the benefits of a continuously-variable transmission. There are other hybrid vehicles available, but as far as I know this system is the only one that's not really an "electrically-augmented internal combustion vehicle", with the exception of the Honda Insight which is a 2-seater. Toyota will be putting it into their Highlander SUV this summer.

For many more details and pictures, I recommend the web site of a Prius owner.

The strangest thing about this car is getting going. Insert your key fob into a slot on the dash, hold down the brake, and push the power button on the dash. The shift-by-wire control is built into the dash as well, so you simply temporarily move the knob to D for drive, and away you go. After that, everything is surprisingly normal - except it's almost silent until the engine turns on. The gasoline engine turns on and off as engine load or electrical loads demand. The window sticker says 60mpg city and 51mpg highway, and even though you'll probably never see those numbers in real life - I think you'll get 40-50 mpg in city driving no matter what. Oh yes, and emissions are reduced by 90% over a conventional vehicle.

It seems to have plenty of power. Although it's not meant as a performance vehicle, you have no trouble whatsoever merging into freeway traffic, for example. It's also got plenty of room - bigger than a compact car.

Right now as they ramp up production - they can't make enough of these cars. I just happened to get to my dealer when one showed up, and there were people in line behind me to buy it. Even at sticker price from $22K to $26.6K, these are very reasonable cars and look pretty distinctive as well.

I ended up buying a Corolla instead, but not because of any shortcomings of the Prius. It was a choice between the high-end Prius which had a bunch of gadgets I don't need, and a $17K car which would do exactly what I needed. Still, I can't help but believe that my next car will be a hybrid.

Space Raider

2005-04-07T11:46:00.000-04:00

I first worked on this driver last year, after Pierpaolo started it. (It's currently playable, but there are plenty of graphics glitches.) Unfortunately, I was unable to make any further progress without access to the physical hardware.

So, now I have the Space Raider board on my workbench, and I'm slowly making progress. It's amazing what one person can do with a multimeter, some databooks, and time. :)

Right now I'm concentrating on the I/O section for the sound cpu. In case anyone's interested, this is how I'm proceeding. First, I found the 5 sound chips and backtraced them to the address decoder for all the IO ports. Now I'm going through ports 0x28-0x2f, 0x30, and 0x38 and figuring out which bits are being used and for what purpose. Ports 0x30 and 0x38 go to a bank of 8 4051 analog mux IC's. They each have graduated resistor ladders connected to them. Maybe they are a fancy volume control or an analog filter. I should be able to get that figured out soon.

Additionally, I'm making up a harness to use to power up the board. I discovered jammaboards.com, and they had everything I needed for <$15. I'm hopeful that I can get a lot more information by actually playing the game! :) It will be very nice to get the grid behavior correct.

Pirates

2005-04-06T12:45:00.000-04:00

I've had some strange thoughts lately about pirates. It came to a head while watching the "Pirate Party" on board the Disney cruise line.

First of all, I am a fan of Neal Stephenson and am currently reading "Quicksilver". Among many other things, there are pirates in there, as it takes place during the late 17th and early 18th centuries.

These were really bad guys. They were sort of like terrorists are today. It took the resources of whole countries to finally get rid of them.

Strangely, children dress up as pirates today. On the cruise, there was a pirate party with pirate costumes and dancing. And this was right in Blackbeard's old neighborhood, as I understand it.

I can't imagine my great-grandchildren dressing up as terrorists for Halloween. It would be nice to think that the problem will be so obsolete by then that it could be possible.

Ok, that's wierd you say. But it doesn't end there.

The Pirate party is clearly inspired by the "Pirates of the Caribbean" movie and ride, an important part of Disney's intellectual property.

But wait - the term piracy now refers to people who steal intellectual property! This is actually something companies like Disney are deathly afraid of today.

So, let me get this straight - the original pirates who murdered, raped, etc. are trivialized/stylized by children and everyone else. Meanwhile, the word pirate refers to people who copy DVD's, and now it's their turn to be stopped by governments and multinational corporations.

So maybe I've got it wrong. Maybe my great grand-kids will dress up as I.P. pirates. That would be much cooler than terrorists. :)

Cruise Review

2005-04-06T12:26:00.000-04:00

Well, I went on the Disney Cruise over this past weekend - so I thought I'd post a short review.

First of all, I want to say that I'm not a big fan of the Disney corporation. I abslolutely hate what they've done to U.S. copyright law. Still, this was probably my only chance to go on a cruise with my family, so I have to deal with the guilt now. Maybe a big fat donation to the EFF will make me feel better.

I gotta say, Disney knows how to put on a cruise. They had everything an adult would want, but also everything kids like. For example, they've got adults-only bars, an adults-only pool, and gourmet food - along with tons of kids activities, foods, pools, etc.

The staff members must be trained to try to help when they hear a kid crying. They were very attentive and entertaining.

The shows were more oriented towards kids, so I didn't get a lot out of them. I believe I described one of them as a "nice review of the intellectual property portfolio" and got a funny look from my wife.

There were stops in Nassua in the Bahamas and Disney's private island "Castaway Cay". They were both nice and much warmer than Michigan :)

The only drawback I ran into was that my son is a little young (3) to enjoy everything they have. For example, they have a play/activities area which you can leave your child in, and they will page you when he/she wants to leave. My son was a bit too shy to be comfortable there without me - but my 7 year old niece never wanted to leave. When my son turns 5 or so, it would be perfect trip.

Demons and Dragons - Part 3

2005-03-19T23:32:00.000-05:00

Well, it's playable now. It's got robotron-style movement, with seperate controls for moving and firing. Moving actually uses an analog joystick, which can allow speed control, but I haven't actually hooked that up yet.

The only thing that's really missing is sound. It writes sample numbers to a port, so there must have been an additional audio board. Hopefully we can dig up more info on this, if the board and/or ROM images still exist anymore.

Demons and Dragons - part 2

2005-03-18T23:45:00.001-05:00

Well, as it turns out - the one piece of Professor Pacman hardware that I didn't emulate is used by D&D. The good news is - I got it working tonight! Now profpac passes all self-tests, and demndrgn runs into the game portion. I need to map the controllers and dips now, since I can't control the player yet.

Right now there is no sound, but it sure seems like it was supposed to have speech! There is a part where a wizards head fills the screen, and his lips move. I wonder what's up with that?

Anyways - pretty neat stuff

Update: in-game screenshots...

Demons and Dragons

2005-03-17T22:22:00.001-05:00

This is a prototype game that is supposed to run on Professor Pacman hardware, or something very similar. I got it run a little bit...but it's not playable yet.

Xen

2005-03-12T08:59:00.000-05:00

I've been watching the Xen project for a while, and I think it's probably time I tried it. I like to play around with experimental OS's like Plan9 from time to time. I'm also hoping to build some custom Linux kernels for a work project.

Xen is Open Source software that allow you to run multiple OS's concurrently, with little loss of performance. It achieves this by actually requiring the OS to be slightly modified to work with Xen. As a benefit, any OS can take advantage of Linux device drivers, as well. As a side effect, it means no repartitioning is necessary to try a Xen-compliant OS.

Unfortunately, MS won't let the Xen-ified WindowsXP be distributed, but other OS's are coming around. The Linux 2.6 kernel is already ported, and some distros are starting to bundle Xen in now.

It will be interesting to see if this is a fad or the way of the future.

Midway Tornado Baseball

2005-03-12T08:55:00.000-05:00

I got one of these PCB's yesterday. The ROMs look intact, so hopefully this will help with the "No good dump known". The auction claimed that it didn't work when powered up, but I'm betting that's mostly due to the missing CPU chip. :)

I'm 37....I'm not old!

2005-02-18T18:03:00.000-05:00

Happy Birthday to me! I've been waiting for about 6 months to use that line (from "Monty Python and the Holy Grail" , a fine flick if you like that sort of thing)

I haven't switched to a new blog yet, since I've been sidetracked by the idea of using some kind of wiki/blog combination. The blog will remain here until I make up my mind.

Square-wave aliasing

2005-02-15T13:06:00.000-05:00

So, I spent a bit of time addressing this problem.

Thank for the comments! First, I did notice that certain frequencies are more problematic than others. Higher frequencies tend to have stronger harmonics which fold over. However, if you have a tone that divides evenly into (sampling_rate/2), the folded harmonics land on top of the non-folded ones, so it sounds ok. Still, it's not right, but it sounds ok. I also know that I could process things at a higher sampling rate internally, and post filter it.

What was bothering me was this - in the "synthesis" problem, I know _everything_ about the waveform I'm trying to generate. So, it seems that using that information from N previous samples, I should be able to come up with a "optimal" solution in some sense.

As it turns out, one approach is to apply a window filter to the previous bit or bits, before generating the samples. The simplest thing is to use a one-bit-long rectangular filter. This is easy - and definitely sounds better than doing nothing. But it doesn't do a very good job as a low pass filter. For one thing, the cutoff frequency is fs, not fs/2 - but it does roll off well before that. Some of the other modules in the discrete sound system do this already as well.

Finally, I experimented a bit using a low-pass filter based on a Kaiser window. This gives great results, but you really need to use at least a few more of the previous sample bits to get decent results. 10 or so is darned near perfect.

Anyways, I'll probably look at some other approaches, including optimal low-pass filter designs, but in the end I'm not sure it's worth doing much more than a rectangular window.

A fine excuse to learn more signal processing, anyways!

Blockade.c sound again

2005-02-15T12:59:00.000-05:00

MAME 0.92 has my simple code for doing the square wave sound. I was hoping to do some sampling of the noise-generator circuit this weekend. However, I made a stupid mistake and ended up messing up my Comotion and Minesweeper boards. :( Nothing serious, but I need to order some parts to get that part of the circuit working again.

You can hear the aliasing distortion that I was talking about in Minesweeper, since it generates high-pitched tones. I'm still working on that, since it's turned into a fun math exercise..worthy of a seperate post...

Blockade.c sound, new blog in the works

2005-02-06T21:50:00.000-05:00

Well, I've got partial sound working in blockade.c. Definitely better than silence!

I'm trying to come up with some simple way to deal with the aliasing distortion you get from generating high-frequency square waves the "simple way". This is really apparent in Minesweeper.

For the mathematically inclined, the problem is described and completely solved by the approach in this paper:

http://ccrma-www.stanford.edu/~stilti/papers/blit.pdf

However, it's a pretty heavy-duty approach - probably too unwieldy for MAME.

I'm also getting ready to move to a blog based on Movable Type. I really want "categories", so that I can blog about anything and not alienate the people only interested in MAME. :) I grabbed avoidspikes.com and I hope to set up shop there within a week or so. I'm going to move my dsplib.com content there as well.

Amutech Minesweeper Cocktail/Standaround

2005-02-01T11:17:00.000-05:00

Well, I got a PCB from eBay. As suspected, it is an exact clone of the Gremlin blockade hardware, except for the connectors. The program roms are the same as our existing set, but the graphics are slightly different. (The scores can be displayed in four different directions).

So, it turns out that fixing the port settings in drivers/blockade.c enables 4 player mode. I did this, along with some general cleanup. I'll submit the updated driver soon, but I'd like to try and add some sound first.

Now if only a 4-player blasto would show up...

2005-02-01T01:42:00.000-05:00

I'm on the blog bus now too. Hi Tim!