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Member Since 29 Sep 2005
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#3225429 What am I looking at? Unfamiliar 130XE mod...

Posted by Rybags on Sat Apr 25, 2015 10:06 AM

Actually, as we found out a year or so ago, many 400/800 machines used a simpler CPU board + the Sally 6502C as well.  Also all 5200 and 7800 machines.


So in fact the "original" 6502B would be by far the minority CPU in 8-bit Atari gear.  Raw numbers would probably look like:

6507 - probably over 35 million as also used in many peripherals as well as 2600.

6502B - probably under 1 million.

6502C "Sally" - probably over 7 million counting consoles.

#3224580 130XE 4 or 16 RAM chip version preferable?

Posted by Rybags on Thu Apr 23, 2015 8:48 PM

4 chip for sure.  Seems that failures of Ram are more common to the 1-bit types, C64 included there also.


Less points of failure.  And if it does go, a whole bunch less work to fix.


Also, the 4-bit 64k DRams were used a lot on PC video cards, so spares are easy to find.

#3223634 Project-M 2.0

Posted by Rybags on Wed Apr 22, 2015 5:50 AM

Same bandwidth though less CPU loss since the timer IRQs wouldn't be needed for mode change.

But doing higher resolution would mean the raycast phase would slow it down a whole lot more.


IMO the 256 colour mode looks way better.  More colour at the price of resolution usually does.

#3218445 Commodore Free issue 86 released!

Posted by Rybags on Tue Apr 14, 2015 4:30 AM

Just strip the rest of the crap from the URL... for some reason this version of the forum software easily corrupts links.

#3215147 Commodore 64 VS Atari ST

Posted by Rybags on Wed Apr 8, 2015 10:43 PM

Game library - sheer numbers, C64.  Maybe double or triple but for both machines into the thousands.  Quality, good and bad for both but the best graphically on ST easily eclipse the C64.


Affordability - not much difference.  Most STs have inbuilt floppy drive but the machine itself will be more than C64 by maybe half.  But you can spend more than the C64 price for a floppy drive for it.


Ease of use - for plain gaming it's not a lot different.  ST autoboots or point/click to load.  C64 usually a simple Load command.


Ease of programming - C64 Basic probably easiest of anything for both to learn/use but close to least capable.  ST has plenty of "serious" languages around.  OK, you can do C, Forth and the like on the C64 but such HLLs can be frustrating in that plenty of memory is used for not much return.


Obscurity - ST is somewhat forgotten in comparison.  From a collector's POV expecting some sort of rarity, don't hold your breath in either case, millions made of both and more than enough of both around to meet demand.

#3214565 Project Veronica

Posted by Rybags on Wed Apr 8, 2015 5:59 AM

It has the advantage of plug & play though, so is much more inviting to the average user.  No opening up the machine, no soldering, no having to use custom OSes.


Though that said, a faster main CPU has the advantage that some games can immediately benefit and some could do so with mimimal modification.

#3213867 Should Atari have attempted more updates of classic games on the Jaguar?

Posted by Rybags on Tue Apr 7, 2015 6:39 AM

No. No. No.


Recycling old titles just contributed to the downfall of Atari.  The pattern started with the 5200 and including Super Breakout when Colecovision had Donkey Kong which is essentially a 5 year newer game.

The rot continued with 7800.  Asteroids (PAL builtin) was ancient by the time 7800 finally made the mass market and even Pole Position II was showing it's age.


At least with the Lynx there did seem to be some new stuff.  Jaguar, although Tempest 2000 is highly praised, didn't seem to bring much new to the table.


Look at practically every other console of the 80s until end of the 90s, almost all had a killer app or bunch of titles that were fresh or not available on the competition.

#3213047 Mario Bros XE

Posted by Rybags on Sun Apr 5, 2015 10:19 PM

The Atarimax cart version probably won't do you any good either.  It's likely just the executable file which will want 128K Ram.

Problem is, Mario Bros XE is a 64K cart where the lower 8K bank switches and top 8K bank is fixed.  Atarimax carts only have the top bank which is switchable.

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#3212987 Creating a custom rom

Posted by Rybags on Sun Apr 5, 2015 8:16 PM

There's no guarantee on stuff like that.


Custom FP - the entry points are all the same so you can mix and match there.  Though there is one version that uses extra Rom space around $CB00 (?) so you need that space free of anything else to be able to use it.


Things like margin, getting rid of attract mode.  The sequence of instructions should be the same regardless of OS version so you could probably just search the entire Rom for the sequence and replace with what you want.


Then once all done, calculate and store the checksums and you should be good to go.  Test on emulator before flashing or burning to Eprom.

#3212501 A8 Elite (Acornsoft):The UK Press Claims-What is the real story here?.

Posted by Rybags on Sun Apr 5, 2015 2:42 AM

Entirely possible a quick/dirty hack could have been done.  The BBC bitmap mode uses the same cell based arrangement as C64 so a working port from source might have been possible in a matter of hours.

Of course probably missing sound and plenty of other stuff that'd take a lot longer to do.

#3212426 Where is the end of memory used by BASIC?

Posted by Rybags on Sat Apr 4, 2015 8:17 PM

APPMHI is supposed to be maintained by the main running application.  The OS uses it to determine if a screen Open operation is permissable.

So, normal mode of operation is that an application like Basic would dynamically update it to reflect it's top of memory.


MEMTOP ($90) is maintained by Basic and copied to APPMHI either periodically or every time MEMTOP is updated.  Probably the latter as the user can upset things by pressing Reset.


The 400/800 OS has a bug where if you set APPMHI higher than the normal Gr. 0 DList starts, then press Reset, the machine gets stuck in an unrecoverable situation.

The XL OS fixed it by use of a flag - if the initial screen open failed, next time you pressed Reset APPMHI would be reinitialized to a value that allowed the screen to open.


Which one to reference?  I'd use MEMTOP.

#3210215 Purpose of memo pad?

Posted by Rybags on Wed Apr 1, 2015 6:34 AM

I'll pay that.


You should add though that a save feature was possible if you connected the optional VCR.

Reloading requires the optional VCR and second TV.

#3207579 RAM not erased after coldstart? (Emulator)

Posted by Rybags on Sat Mar 28, 2015 3:52 AM

The OS only clears what Ram it finds, that can vary depending if a cartridge is inserted or if Basic is enabled or not.  And can vary again if it's a switchable or bankable cartridge if the system restarts but not as result as powering off.
In "proper" emulation the Ram should assume a random pattern or pattern resembling what the real thing does but many emulators just zero everything.
I think Altirra now tries to do what happens on real hardware, would need to do some digging to work that out.
Passing information across a coldstart - on a 64K system it's easy enough since there's 16K of Ram under the OS that goes undisturbed.
On a 48K system - I don't think it can be reliably done.
You can force a disk reboot without doing a coldstart/Ram clear - use a CASINI routine that gets called on warmstart.  In that routine, clear the BOOT flag (9) and WARMST flag (8 ).  When you return, the OS will attempt to boot from disk (so long as a cartridge that disallows disk boot isn't inserted). Call the warmstart vector when you require the boot - JMP $E474.

#3206870 Purpose of memo pad?

Posted by Rybags on Fri Mar 27, 2015 12:33 AM

The extra overhead in Rom is even smaller than I'd thought.  A little over 30 bytes.

The subroutine to print a line of text to E: is needed anyway for Boot Error.  The reading of text is JSR to a routine which calls the E: get character vector by pushing the address to the stack and doing RTS.

#3206380 Purpose of memo pad?

Posted by Rybags on Thu Mar 26, 2015 10:28 AM

The problem there is you end up with a (probably harder to use) Kim-1 successor.


Maybe the best compromise would have been colourful Atari logo with 4 line text window.  And give it a couple of commands that actually do something like boot disk, boot tape.

Then again, if the Rom space was available my vote would have been MLM or a partially resident Dos.