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gdement

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Posts posted by gdement

  1. Posted · Edited by gdement

    The zapper reports back light/dark to the console every 1/30th of a second. This relatively slow rate means the zapper can be a dumb device and let console can deal with the timing issues itself. It also means you don't need a photoreceptor that's anywhere near as fast or sensitive.

    Interesting. So if it only reacts in 1/30 sec intervals, then I guess scan timing would be impossible on the zapper.

     

    I'd guess that most electron-beam based guns have additional circuitry to assist with the horizontal position/timing as well. If they were dumb devices you're looking at about 80000/s worth of light samples to transfer and process. (assuming 80 pixel wide resolution)

     

    Using the 7800 as an example (just because I'm more familiar with it), there's 80 6502 clock cycles in the visible range of each scanline. (going by the "7800 software guide" PDF)

     

    I got curious so I typed some untested, probably broken pseudocode for polling a light gun (see below). I don't actually know how the 7800 gun is programmed, I'm just guessing here.

    It looks like it could be sampled at least 5 times per scanline, or 6 if you don't mind them being unevenly spaced. The uneven spacing is consistent so the code can still resolve it accurately.

     

    Either way, 5-6 samples isn't very many. However, you could stagger the starting point on each scanline to get more useful resolution.

    That would give 80-96 horizontal positions checked within a vertical tolerance of 16 scanlines, or 40-48 per 8 scanlines, whatever. That might be reasonable, but I don't know if they really programmed anything that way.

     

    You might be right about the gun having assisting circuitry. I didn't think so, but the 6502 isn't as fast at this as I thought it would be. :)

     

     

    <Maria is disabled while scanning>
<set scanline counter to 0>

NextLine:
ldx #5      ;sample counter.  We can do up to 6 samples per scanline
<use scanline counter to calculate an appropriate stagger value for this line>
<use WSYNC to sync with start of scanline>
<use nop's or some other method to stagger the start of sampling>

ScanLoop:
lda   GUNSIGNAL           ;6  ;(RIOT access will slow it down by 50%) I'll imagine it returns 0/1 depending on result
beq   SAWLIGHT            ;2 (when not taken)
dex                       ;2
                         ;unroll the loop here to squeeze in 6 samples instead of 5
lda   GUNSIGNAL           ;6
beq   SAWLIGHT            ;2
dex                       ;2
bpl   ScanLoop            ;3 (taken until done with sampling)
                         ;23 cycles per 2 samples  (we have 80 available after WSYNC)

<increment scanline counter>
bne NextLine  (always taken)


SawLight:
<decode the counter and decide where we hit the screen, etc>
<X tells us which sample on the current scanline was a hit, and the scanline counter tells us what line>

     

    Unrolling the loop above does mean the samples aren't evenly spaced. To make them even, roll it back up and get 5 samples instead of 6.

  2. Posted · Edited by gdement

    Yeah, I've had trouble with mine also (NTSC). It works okay on a conventional CRT television, but I thought something was broken when I hooked it up to my TV tuner card in my PC. I could hardly see anything.

     

    The signal probably isn't quite "standard", and modern TVs/tuners might be more picky about it.

  3. Posted

    I see no reasone, especially a newer LCD with a 8 or even 4 MS refresh rate couldn't do it, as long as it's in sync with the system. But just playing the games, I can feel the lag on most TV's, so I don't know, a lot of modern consoles have lag built in to handle the problems.

    Every LCD has input lag (not the same as refresh rate), so it wouldn't work without reprogramming the game to be aware of that issue.

    At minimum, there's the lag of waiting for the entire frame to be transmitted to the screen before it can be displayed. This means at least the top portion of the screen will be almost 1 frame behind, even in the best possible case.

    In that best case, some NES games might be tolerant enough to work.

    Anyway, I've only heard of very few LCDs that might be this fast. Nearly all of them have more significant lag.

     

    I think new games could be programmed with a calibration screen, which would measure the lag of your display and keep it in mind during gameplay. This would require the lag to be consistent, and it might not be with some displays. They'd also be forced to use the light/dark method obviously.

     

     

    The big N used the light/dark method to lower the cost of the gun.

    Is it really any different than other light guns? I thought the difference is just in the programming. I don't see why a NES game couldn't be programmed to use scanline timing. It apparently wasn't convenient though, probably due to the way that system handles it's graphics.

  5. Posted · Edited by gdement

    I think my most valuable games are actually computer games, not console:

     

    Ultima: The Second Trilogy - Limited release version with all cloth maps and a sticker on the box. I'm a bit confused about this one, because an article online says that this version was only available by preorder. I got this as a gift, and I could have sworn it was already on the shelf by then, I never had any impression my parents preordered it. Until recently I didn't know that most of these had paper maps. I'm glad I lucked out on that.

     

    Ultima: Martian Dreams - not as big a deal to me as the 2nd trilogy, but apparently this is somewhat rare. I couldn't find anyone selling it on ebay except 1 high-priced store listing, so maybe it's value compares with 2nd trilogy.

     

     

    My console games are mostly cheap. I don't know which of these would be highest:

    Michael Jackson's Moonwalker (CIB) - This went crazy a few months ago

    Phantasy Star (CIB)

    Pac Man Jr (7800 homebrew)

     

    It gets cheaper from there.

  6. Posted · Edited by gdement

    told me that Dacman was not my game and it took me weeks to understand what he did means by that because I certainly programmed that rom, but PacMan is not my game, it's someone else game. Same thing for Breakout and Bejeweled, and I wanted to be appreciate for something, showing what I'm capable to, and I did it... but it's all wrong apparently.

     

    I don't know the person you mentioned, but

     

    I think many non-programmers have a misunderstanding that stems from the word "port". Many seem to believe you can just plug in the ROM for arcade Pac-Man into some sort of "conversion" process, and get a Coleco/Atari/whatever ROM out the other end. They don't realize that the game has to be written from scratch, 100% your own code, and is thus just as difficult as any original game would be. Because it looks like an existing game, they think you copied something.

     

    Many people also don't appreciate the technical challenge involved with writing a computer program. There were several washouts in my earlier programming classes, and I'm pretty sure none of them realized what they were getting themselves into.

     

    Writing a complex program is something I'd compare to writing a novel. It's sort of like art for engineers.

  10. Posted

    I've seen Genesis with issues (like the color goes out) but mostly it's fixable problems. Genesis is one of the mostreliable systems from the late 80's out there.

    I would agree if you said early 90's. :)

     

    I don't have a big sample to draw from, so maybe it's just me.

    But I think the 1989 Genesis, though awesome, is crap for build quality. The ones from 1990 onward are good though, I've never known of those to have anything wrong with them.

    They went through lots of board revisions, and the early boards have lots of rework on them. Mine has had problems come and go ever since it was about 1 1/2 years old. All the hack-job rework on the board tells me it must have had design problems. At first I thought mine was just an unlucky unit that had to be modified to pass QC, but then I saw photos online of that same rework on other people's boards, so it was apparently "standard" for the early revisions.

     

    I bought it in mid-1990, and it was already having problems by early 92, so I didn't think much of it quality-wise - my NES was more reliable if you can believe that. A friend bought one a couple months after me, his was always perfect and given the timing I suspect it had a later/better board. Mine was already bought awfully late to turn out to have 89 dates in it.

     

    Most recently I fixed a video problem, but it's having a recurrence of controller glitches (which first happened in 1992) and apparent Z80 instability. I may have narrowed down the problem though so I'm hopeful.

     

    I recognize that maybe I'm the only one to have problems with it, but all the board rework tells me there were genuine issues with the early Genesis.

  11. Posted · Edited by gdement

    Horizontal can be either 160 or 320. Both modes are possible. Also, the resolution can change mid-screen. Many games have 320 resolution in a status bar area (for text), then drop to 160 resolution for the gameplay area (160 mode is faster and more colorful). I imagine emulator screenshots would all be rendered as 320 pixels though.

    Actually, since the 7800 pixels aren't square, the emulators might upscale them to look correct on a computer monitor, so getting 1:1 pixel screenshots might be a problem.

     

    The vertical resolution is technically 243 lines (from the "7800 Software Guide").

    According to something I found in some code, I think the PAL output is 293 lines.

     

    This exceeds what will actually fit on a CRT television, so only part of it is normally used. Exactly how many lines get used would be up to the programming. That's why vertical might be different with almost every game.

     

    Unused scanlines would be blank, I don't know if the emulators actually detect this and crop them out of the image, but maybe so.

     

    So basically, the theoretical resolution is 320x243 NTSC, 320x293 PAL.

     

    In practice, most scanlines in most games will be rendered with double-wide pixels, and only about 192-200 or so (NTSC) scanlines are reliably visible on all televisions.

     

     

    [edit: added PAL info]

  12. Posted

    Sounds like with the way you had it hooked up, the VCR is what was tuning into the RF signal and providing the audio output to the speakers. Since it was better when you tried using the TV's tuner, the VCR might be the culprit. If you happen to have any other VCRs handy I'd try a different one.

    There could also just be a volume setting on the VCR that was set too low, but I don't think I've seen a volume control on a VCR before.

  13. Posted · Edited by gdement

    You may have already checked this, but make sure the cable you're using is actually good. I found a big difference between cables with my 7800. I'd also try a different TV if possible.

    My 7800 apparently has pretty bad output. I had a horrible time getting a decent signal to my computer's TV card, then when I hooked up to a regular TV it was much better. So the quality of the tuner in different TVs might also make a difference.

     

    Is the background noise consistent with graphics appearing on the screen, or is it just constant? If it seems affected by the screen image then it's probably interference between the video and audio signals, possibly originating in the console itself or it could be the TV's fault.

     

     

    By the way this sound is coming from a separate pair of speakers, not the television itself.

    How are you getting the signal to the external speakers? Is the TV outputting line level output - or is it outputting according to the volume setting? If the volume on the TV is too low, and then you're amplifying it at the speaker, that might cause hissing.

     

    Do you get good audio from the TV speakers? If so, then that narrows it down to a problem between there and the external speakers.

  14. Posted

    I really liked Paper Mario, it's much more fun than I expected.

    Exploration is good, with lots of important secret items to find. But I especially like the battle system. It's more interesting than most turn based RPGs.

    It was fun to take risks in that game because how well you play the battles makes a big difference to the outcome. If you play them well enough, and plan your moves carefully, then you can beat much stronger enemies than you otherwise would. Finding and setting up badges also makes a big difference.

    Although on the surface it just looks like a kid's RPG, it has a lot more complexity than I expected and is actually more rewarding and interesting than the average Final Fantasy game.

  15. Posted

    They need to have better handling of subcategories. Many of them should be treated more as filtering attributes rather than separate categories.

    For example, if you're looking in the NES "games" category, it should also include all the subcategories like "new in box" etc. It seems to force you to look in each subcategory explicitly in order to see them.

    Same would apply to the C64 - they could list those games in a "computer games" category but have a subcategory for C64. If they did it this way people could browse as general or specific a category as they want.

  16. Posted

    I bought a "Sega Arcade Power Stick" on ebay, which arrived here yesterday. This is the 3-button Genesis joystick that everybody raves about, and I wanted to try it out.

     

    The one I bought was advertised as "mint condition", but "as-is, no returns" from a seller with 4.9 stars in every category and 100% fb.

    This shows how useless and inflated the feedback system is.

     

    The only thing "mint" is the cosmetic appearance. It's clean.

    But the controller is obviously worn out. First my minor complaint - the C button binds when pushing it at an angle, which is clearly a result of wear since the other buttons aren't doing that.

    But the big problem is that the joystick is broken. Specifically, it doesn't have any autocentering from the right side. If I push it to the right, it will just lay there without recentering itself. If I push left and release it, it will sometimes throw itself all the way to the right.

     

    I haven't tried opening it yet, and I probably will soon, but is this something simple to fix? Or should I just toss it? I'm hoping it's just a broken spring, but of course I have no idea where I'd find another the correct size, except by salvaging another joystick which would be pointless.

     

    I tried playing Castlevania Bloodlines with it (great game I also bought recently) but it's no fun with 5200 style controls.

  17. Posted

    I made another try last night, but had a terrible game. This is the Castlevania I remember.

    I died *twice* on the 2nd level. One was a classic medusa-head-knocks-me-into-pit maneuver. Oh how I used to lose my temper at that exact spot...

    Then I died 2 or 3 more times on the 3rd level, ending my game.

     

    I don't remember why, but I got to the mummies with 1 hp left and no way to hit them from above. So I died.

    Starting a new guy at the end of level 3 sucks. It's very hard to deal with the fireball statue things without a long whip. I got back to the boss another time but didn't have enough health or weapon to win.

  18. Posted

    It still would have been better if Sega had found a way to power up those things without the need of additional AC adapters. Admittedly, the Adam's way of powering up the thing through its printer was stupid, but I think consolidating the powering of so many adapters hooked up to the main system was a better idea than what was handed to the Sega CD and 32X.

    They should have designed the expansion port to carry power from the CD to the base console.

  20. Posted

    post-5182-12560223462_thumb.jpg

    89,200

     

     

    I had a clean run going, then I hit stage 4. I lost most of my lives at the beginning of that stage.

    Still, I had the holy water as I got to frankenstein, which is the only way I can beat him. But I messed up and the monkey dude got loose before I hit them. After losing the holy water I had no chance with my last life. Those snake things before the boss sure give out a lot of points though.

     

    It's funny how hard stages 2 and 3 used to be when I was younger. I used to lose my temper on stage 3 especially.

    They're so much easier now it doesn't seem like the same game I remember, but I'm using a real cart so I guess it is. :)

    Now it's 4 that starts killing me. I guess I'm getting better, maybe I'll beat this game before I die.

  23. Posted · Edited by gdement

    The only game on the list that I've played for very long is Wizardry proving grounds. Knight of Diamonds is pretty much the same though (I didn't vote).

     

    I like Wizardry, but it's a niche. There's not really any story, so you might not like it for that.

    The most notable thing about it is that character death actually matters, you don't get cheap and 100% successful resurrections. So far I've had a few deaths which I resurrected (at great cost), and 1 which permanently killed my lead fighter. That didn't upset me, since I knew that's part of the game's challenge. You don't automatically win just by playing, you have to manage your characters and expeditions carefully.

     

    The death thing will either be cool to you, or you'll hate it. I like it - it gives a sense of real danger while playing the game. When you see 1 of your characters in trouble during a fight, you will be scared, not bored.

    I keep a roster of bench players and mix up the party assignments, so I don't have all my eggs in one basket. Even if I lost a full party of 6 characters, I wouldn't be starting over. I have others that aren't far behind in development and they could recover the bodies before long.

     

     

     

    [for better graphics/sound/etc, there's also Wizardry 5 on the SNES, which is still the same style of game]

  24. Posted

    I'm now completely convinced that the 100uF 10v Chhsi caps in these early Genesis boards, are crap. If you have those on your board, be suspicious of them.

     

    I say this because I replaced some more caps in this Genesis, this time caps that aren't under the heatsink and don't have the heat to blame. I found that once again, all the 100uF 10v Chhsi that I pulled were way out of spec, but the other brand (Elecon) were generally okay. I've not yet found a single Chhsi that's good.

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