Jump to content

Rybags's Photo


Member Since 29 Sep 2005
OFFLINE Last Active Yesterday, 11:10 PM

#2986637 Emulation in YouTube Videos. Yea or Nay?

Posted by Rybags on Fri May 9, 2014 5:51 AM

Doesn't matter.  You use the best you have available.


Not everyone has a capture card or dongle handy.


I'd prefer a colour-errored emulator capture complete with it's filled graphics rather than CRT scanline artifacts to a hamfisted camera job (usually complete with irrelevant background noise and barely audible sound from the actual device being recorded).

#2985885 Any 2600 titles from back in the day still impressive?

Posted by Rybags on Thu May 8, 2014 2:42 AM

Space Invaders still stands up - except for those missing columns of invaders it does everything you'd expect in a home port.

Other complaint being that on the easiest level you can prettywell go forever, and the 4-digit scoring becomes another sore point.


Chopper Command also still looks impressive - in fact a lot of the Activision games could be passable Flash or mobile-based games today.

#2983691 7800 hardware facts

Posted by Rybags on Sun May 4, 2014 5:30 PM

Doesn't Maria use the /HALT always when doing DMA?  There is no requirement there to wait for the CPU to finish an instruction.  It's only when using /RDY that there's the possibility of 3 successive writes by the CPU before it actually stops.


Possibly the varying startup time could be due to the fact the CPU might be executing a long cycle?  And DMA difference for RAM vs ROM?

Long shot - maybe a long cycle has to be followed by a short cycle?  Maria decides not to halt until it can be sure an RMW instruction involving TIA or RIOT has finished?

#2982465 7800 hardware facts

Posted by Rybags on Fri May 2, 2014 11:26 PM

Weird... maybe run the code from RAM, but I don't see why the result would be any different.

#2981873 7800 hardware facts

Posted by Rybags on Fri May 2, 2014 10:02 AM

A "long cycle" automatically inserted at some point might make sense in that cycle alignment vs beam position would be consistent among scanlines (assuming none generated by TIA/RIOT accesses) although cycle-exact timing is much less important to programs than on the computer line.


7800 uses the exact same master clock as the XE computers.

Computer has 262 lines * 114 cycles = 29868 per frame

7800 with 263 lines * 113.5 cycles = 29850.5 per frame - 18.5 cycles less, which in fact might be "convenient" given the computer's framerate is in fact slower than analog broadcast standard.


7800 with 263 lines * 114 cycles = 29982 cycles per frame - which would be slower again than broadcast.


Wouldn't an easy way to test such theories be to just do a program that does a background colour change halfway through a scanline, then does a software wait equal to the exact number of cycles in a frame?

#2980486 Has anyone seen "Once Upon Atari"?

Posted by Rybags on Wed Apr 30, 2014 11:10 AM

Got it here somewhere... from memory something like 4 episodes about 1/2 hour each.

#2980371 Microsoft Basic II as an EXE, does it exist?

Posted by Rybags on Wed Apr 30, 2014 6:18 AM

String array would probably need to be like A$[2]


But really you can do without it.  Doing conversion of existing MS type Basic programs is the main problem.  If starting a fresh program then you can adjust your technique and do a sort of emulation.

#2978975 Atari's Landfill Adventures, I now have the proof it's true.

Posted by Rybags on Sun Apr 27, 2014 11:22 PM

It'll be up as a torrent probably 15 minutes after airing.

#2978307 BASIC Ten-Liners - Contest 2014

Posted by Rybags on Sun Apr 27, 2014 7:07 AM

4. Escape 10


Thanks for the votes.  TBXL version a last-minute thing - actually I think only 1 or 2 statements differ.

I'll have to get started earlier for next year's one, although I had this one practically done a month ago but left it to the last day to add the chset and put the final polish on.


#2978231 Fast Trigonometric Functions?

Posted by Rybags on Sun Apr 27, 2014 1:20 AM

Various things can be done/used.


Lookup tables.  Algorithms for fast (but not real accurate) square-root.


For setting an object trajectory to move towards another, the Bresenham algorithm (used for line draw) could be employed.



In the line-draw, either X or Y is always inc/decremented by 1 each iteration, the other axis is fractional, and the movement decision is made by a simple add or subtract then compare operation.


As an alternative, you could use the delta component from initial line-draw calculation as a table lookup value, have a table with 4, 8, 16, <whatever> sets of H/V velocity values per quadrant.  It wouldn't be an exact path but close.  On-the-fly updates would increase accuracy, plus once two objects are fairly close, the accuracy becomes much less important.

#2977085 Re-using the first bit in color related variables?

Posted by Rybags on Fri Apr 25, 2014 7:26 AM

The lsb is ignored/unused in the hardware registers, so with a RAM shadow you could use the bit for other purposes.


Not as handy as the msb of course since 6502 can easily test it with a single instruction, plus the N flag usually reflects it's state after many operations.


If you wanted to use the msb in assembly, easy enough, you could just adjust your colour value stores, then when copying to the hardware registers, e.g.





#2976925 Why did the Atari 2600 console design change so much

Posted by Rybags on Thu Apr 24, 2014 10:24 PM

The original design is complex and probably cost 3 times or more that of the jr to produce the shell.

Even the 2 moved switches early on would have saved a few bucks.


Also throw in the fact that the original case is over twice as volumous as it needed to be with deletion of inbuilt speakers.


Visual appeal lost out in the end.  The design alone makes the early models collectable and displayable, the jr just looks like any other piece of cheap electronic junk.

#2975720 BASIC Ten-Liners - Contest 2014

Posted by Rybags on Wed Apr 23, 2014 8:52 AM

Here's mine - "Escape 10".


It's a mini, downfeatured version of my Moon Shuttle game - guide your ship through the growing asteroid field and through the gap in the force-field on the right (only to have to repeat it until end of game).


Bonus pickups - (L) for extra life

(I) gives temporary invincibility - grab this then just run over rocks and don't worry about the force-field for the remainder of the level.


Game uses some custom characters, so there's a bit of a delay each time it starts.


Attached File  Esc10.zip   1.95KB   40 downloads


ESC10.TBA - TurboBasic Version

ESC10.BAS - version that runs on normal Atari Basic.

#2973124 Last Ninja on C= Plus4

Posted by Rybags on Sat Apr 19, 2014 8:37 PM


All the graphics are multicolour, ie 160x200 effective resolution including the ninja.

Just one enemy appears, graphics are the same as the ninja for him.

I would think they're using multicolour bitmap mode, this allows 2 fixed colours and 2 colours controlled by cell attributes.

#2972521 Is anyone else interested in a better Donkey Kong Jr.?

Posted by Rybags on Sat Apr 19, 2014 12:01 AM

The music + effects from the computer version are pretty good, why not just borrow those?