demo loads perfect on atari 800XL #1, but fails on #2

[Marius]

Hi,

 

This is the Issue:

 

Atari 800XL - stock 64KB - 1050

Demo: Overmind Disk Side A

 

It runs perfect from start to the 'turn disk' part.

 

 

Atari 800XL - Ultimate 1MB (set to Default XL/XE 64K settings, everything else is off) - same 1050 and same Floppy

Demo: Overmind Disk Side A

 

It runs perfect, till the red 'flames' (almost at the end of the floppy) and then it does not continue (So the flames keep burning).

 

 

Tried it several times... keeps failing, always on the same moment in the demo.

 

And now it comes.

When I boot the 100% same disk as ATR it runs on both Atari's completely error free.

 

 

I'm puzzled. Who has a clue?

[Marius]

Oh and base memory on both Atari 800XL computers is 100% error free. So no bad ram.

[Rybags]

Just tried in emulation - it looks like it uses it's own SIO routines, won't boot with SIO patch.

 

Possibly it's hitting the PIA at some wrong address or in a way that upsets U1Meg. U1Meg has registers in the $D3xx area.

 

Actually, that's something I should have tried, I'll see if it hits anything "wrong" in that area and post back.

[Rybags]

Nope - doesn't seem to have any writes to $D380-$D3FF once it gets started.

 

I'm not sure what key/buttons are used to skip throughout, but it seems to check the SHIFT key at the disk flip prompt.

 

Maybe try it again then try various key/joystick button combos.

[Marius]

But that does not explain why the demo runs perfect from Sio2SD (ATR) and not from 1050, which is the same data (I created the floppy from that ATR).

And the floppy is ok, since it works perfect on another Atari.

 

The only thing I can think of is that there is some kind of difference in 'impedance' between the 1050 and the Sio2SD interface, and that the failing atari has a slight defect.

It's a part in the demo where is sound and data I/O together. Probably heavy for pokey. Perhaps the Sio2SD is not as heavy as the 1050?

[Rybags]

Unknown - I've got all that hardware but none is setup at the moment so I can't check for myself.

 

Does seem weird though. Is the 1050 the only device on the SIO chain when you run from that?

[Marius]

I have on this chain:

 

Atari 1050 - Atari 850 - Sio2SD

 

But I also tested it now with only the 1050 and still same issue.

 

It is very weird, since this demo is so far the only one with issues. I have been using the atari with U1MB for weeks without a single issue. But I 'have to' know why it doesn't work. Although the floppy works on another atari, I guess I try to write another floppy disk of the working atr. Perhaps that one will work (or not).

[Rybags]

Did you try other OS versions within the U1Meg? That's another thing I'd not considered greatly.

 

Usual 800XL OS is the one that halts if you swap out a cart, another common XL OS does immediate coldstart although it's more often seen in 600XL.

[Marius]

Well now it works. I recopied the disk, and now I see that my non-working disk has indeed not all the sectors copied!!! (It is a Medium dens. disk, and the target was only copied as Single Dens.). I think that when I tested this floppy on the other atari 800xl, that without me noticing the Sio2SD has booted in stead of the floppy (I completed the first side of the demo completely on the other atari 800xl).

 

So this mystery is solved. The disk is now playing, and I already am watching the backside, so my atari is not defect nor is my 1050 or floppy.

 

Thanks again rybags!