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Member Since 29 Sep 2005
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#3350469 What's the latest Atari related thing(s) you've bought on ebay?

Posted by Rybags on Wed Oct 21, 2015 10:42 PM

Only loosely Atari related and not eBay or even paid for.


A C64 slimline, 1541-II drive and power supplies for each.  Free, courteousy of my local dumpster.

There was a container of floppies (copies) as well but I left them.  Don't really trust media that old when I don't know it's history.


Tried them out yesterday, work just fine.  The disk drive has some cracked plastic in the vent slots.  The computer looks a bit sad and kb is badly discoloured.

#3349914 Coldstart without Power off and cartridge hardware mods

Posted by Rybags on Wed Oct 21, 2015 7:07 AM

The best method by far is a custom OS or device such as IDE +2 which allows coldstart by menu option.


The switch for cart sense is known as "Freezer" among others.  It's a good method though I think the best way there is to invert whatever signal is present so it works whether a cart is present or not.

#3349249 Star Raiders Source Code to be released?

Posted by Rybags on Tue Oct 20, 2015 10:41 AM

I reckon more stars = better.  More explosion particles = better.

Fairly sure there's already a hack out there that reduces particle count to make explostions less lag inducing.


I also reckon forget 8K Rom, 8K Ram.  16K Rom straight up means nice big lookup tables if needed, a couple of custom fonts, ability to add graphical detail e.g. internal details of our spacecraft.


Porting - I've also had that thought.  It would likely be very appreciated on the likes of C64 & Plus4 though it does sort of become a bit sacrilegious.

#3348792 Star Raiders Source Code to be released?

Posted by Rybags on Mon Oct 19, 2015 6:25 PM

The done thing in the early days was leave OS Ram well alone unless you're actually dealing with the component that uses it.

Also note it's entirely possible SR was in development before the OS was even finalised.


The funny thing is, running as a diag cart is more trouble than it's worth since you have to perform system initialization yourself.   The copy protection benefits are near non-existent, the insert/copy to Ram method works no matter what mode the cart runs in.


Later games (e.g Donkey Kong?) use the method of run via the cart Init vector and don't return.  This lets the OS do almost all system initialization but disallows any booting and gives the cartridge control before the screen device is opened.



Potential problems of moving indexed stuff to z-page:  if there's references which for whatever reason use a large offset which cause wraparound on page zero.  Otherwise there should be no problem.

I would suggest if moving stuff to z-page.  In initial testing, leave as absolute instructions.  Put a trap in Altirra which detects any memory access to $100-$17F.  If none occur then there should be no risk of address wraparound and the instructions can be changed to z-page.

#3348074 Star Raiders Source Code to be released?

Posted by Rybags on Mon Oct 19, 2015 12:03 AM

The forced absolute mode would be so that it doesn't inadvertantly wipe all of Page zero out.  Note that in zero-page indexed modes there's address wraparound.  By using absolute addressing it just means the first 100 or so bytes of the stack get wiped.

#3346743 Project NXTXE

Posted by Rybags on Sat Oct 17, 2015 4:20 AM

Sounds cool.


But I would suggest re video output.  RGB at 16 KHz isn't practical in the modern day, there's virtually nothing out there that works with it.  A little extra effort for Component video which has widespread support though that's dwindling now (in part due to DRM).  Or a bit more for HDMI.


Additionally I'd request - if fullscreen video is buffered then provide support for PAL blending on both system types.  Maybe even allow PAL operation mode with video buffered and displayed at 60 Hz.

#3346187 Anyone recognize this 800 switchable rom?

Posted by Rybags on Fri Oct 16, 2015 9:36 AM

In returning to the original question, my guess would be a switchable OS.

In that case no need really to pull anything apart, a dump could be made with a Basic program to disk.


As for the OSes my guess there would be stock Rev B and probably OmniMon + Newell Fast FP on the Eproms.

#3346102 Star Raiders Source Code to be released?

Posted by Rybags on Fri Oct 16, 2015 7:20 AM

A quicker way might be to just throw the original Rom into IDA Pro.  Set the labels then edit in the comments from the scans.  Could speed it up by a huge amount.

#3341190 The new device - True Interlaced Mode Graphics - preorder.

Posted by Rybags on Sat Oct 10, 2015 2:44 AM

I wouldn't worry about it too much.

Many people specifically keep CRT TVs and monitors for the purpose of using with old computers.

It wouldn't surprise me if you did a survey that over 2/3rds still use a CRT with their Atari.

#3340978 The new device - True Interlaced Mode Graphics - preorder.

Posted by Rybags on Fri Oct 9, 2015 6:32 PM

PAL blending between 2 frames doesn't work, it's only good for adjacent scanlines on the one frame.


Doing stuff like colour switches between frames in my experience didn't gain anything over what it looks like in non-interlaced mode.

#3330269 Software sprites: too much complicated on Atari 8-bit

Posted by Rybags on Fri Sep 25, 2015 8:07 PM

Heaven posted a thread about Zone Ranger.  It uses a brute-force Ram based  method for rendering the softsprites.

Costs a fair bit of Ram but the return is you get almost the fastest rendering possible.


From memory there's a routine that covers every possible Y position with the load/store operations embedded.  Before calling, an RTS is inserted at the relevant point and the entry point is variable depending on Y start position.  Then once returned, restore the RTS to what was previously there.

#3328103 Modern Atari BASIC: Convert Brandy BASIC or Start from Square One?

Posted by Rybags on Wed Sep 23, 2015 7:20 AM

With no graphics or sound, it's sort of a case of why bother?

May as well just do a generic MS Basic implementation.

In fact, take away the graphics, sound and string handling and Atari Basic becomes barely any different anyway.


But on the other hand, even graphics and sound support to the level the OS provides would fall way short.  Plenty of games rely on custom DLists, custom character sets and PM Graphics.

#3322618 List of 8-bit computer hardware palettes

Posted by Rybags on Wed Sep 16, 2015 12:53 AM

Agreed on the bollocks idea.  A lot of these sorts of pages are what you could call "informal information" and don't really give true representations of machines capabilities or what a typical user could expect to achieve themselves.


9 colours without tricks is a furphy anyway, we can have 23 colours using mixing though with limitations on what they are and how often they can appear of course.


I'm fairly sure I published an APAC version here some time ago (like probably 2008 or earlier).  A TIP version would probably be worth a shot as would a PAL colour blended 16 colour version (4 colour one line, 4 luma next line).

Not to mention a Rastaconverter version, it might well look the best of the lot.

#3317073 Software sprites: too much complicated on Atari 8-bit

Posted by Rybags on Tue Sep 8, 2015 3:42 AM

It's not that much harder.  And I don't see the logic in using division instructions, they take lots of cycles.

On both 6502 and 68000 all that's needed is bitshifts, AND instructions and additions to calculate addresses and offset for the softsprites.


What 6502 is lacking is instructions to do multiple operations or to do post-incrementing.  But really, the principle of doing softsprites is virtually the same.  The main differences being that the memory layout for bitmap is linear on the A8 rather than interleaved bitplanes on ST, and that A8 also has character modes.

Softsprites are more complex to render in character mode but the restore process is much easier and faster.


There's various threads around, there are multiple levels of complexity of programming for softsprites with the criteria generally being how much memory do you want to spend and how much CPU do you want to save... the obvious tradeoff being that the more memory you devote the faster you can make the process.

#3314432 Altirra - Mono/stereo problem

Posted by Rybags on Fri Sep 4, 2015 7:11 AM

The only change I would propose - if a mode switch is done on an "active" machine, put the Pokey/s into an active rather than init state.  Changing modes midstream tends to be problematic as stereo detection is generally something that's only done once.