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twh/f2

VBXE issue / Great American Cross-Country Road Race

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Hi everyone,

 

is anyone aware of an VBXE compatibility issue with the legendary "Great American Cross-Country Road Race" ?

I usually don't experience any issues with my setup (130XE with VBXE) but I can't get it to work on my hardware.

 

The games seems to start normal but after the introduction sequence with the credits, the screen turns into black and the game seem to crash.

 

I know that a very very small set of atari games have indeed VBXE issues (for instance Gyruss). I don't recall the technical reason for it, but would be interesting to know though.

 

greetings,

twh

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Having VBXE installed in 1200xl together with U1MB, I never had a problem with this particular game.

 

Re: Gyruss

I downloaded fixed version for VBXE from atarionline.pl

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Does it make it past the intro part where the car leaves a trail of smoke that fills the screen?

 

Having a quick look in a 130XE 128K config with VBXE also providing system Ram (which should equate to running R - Rambo Core).

There's no writes hitting VBXE registers around $D600-$D7FF from boot time until starting/playing a race.

 

One thing that might be an issue - at least 2 points during the intro (first just after tumbling Activision logo) the game writes zeros entirely from $D300-$D3FF.

There is a chance that possibly yours is causing the wrong Ram bank to appear @ $4000.

Strange thing though is that such a problem should also occur on the emulator.

 

If you can, try and set your system to run just the "A" Core - that will give you only a 128K base system without the Rambo emulation by VBXE.

The utliities disk should have what's needed, without need to flash another core you should have an A suffixed core present on the board.

Once done you can use it again to revert to the R core if you want.

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The game does a full reset of GTIA a couple of times during the startup sequence by clearing $D000-D0FF. Any writes to $D080-D0FF cause VBXE to reset. That shouldn't be a problem here since GTIA is being reset too, but I know of at least one game that breaks on VBXE because it has an accidental stray write to this range every frame.

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I considered that... but doesn't that write to GTIA only reset VBXE graphical functions and Ram banking being done by MEMAC ?

 

For PORTB banking there should be no effect. Though it'd be interesting to see how a patched game without the register resets goes.

Haven't tested on my 800XL, it's not set up at the moment.

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VBXE has a CFGDIS pin on the J1 connector.

If you set it to HI, all those games that write data to $DXXX will work.

However you need to restore it when you want to update the core of the VBXE (which does not happen so frequently).

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post-29824-0-13912500-1457864509_thumb.jpg

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Ok. My newborn son kept me busy the last weeks. So that I couldn't test on different core settings earlier.

But here are my findings for my particular setup : 130 XE PAL, VBXE2

 

Tested cores:

* FX 1.26 A

* FX 1.26 Rambo

* GTIA EMU 1.06 A

* GTIA EMU 1.06 Rambo

 

The XEX (cassette) version always works - It is missing the intro sequence. So I guess no gtia resets here.

 

The disk version:

* Never works on cores FX Rambo nor GTIA Emu Rambo

* Always works on FX and GTIA EMU without Rambo (Antic-only 130XE only)

 

I did several tests - it's reproducable on my setup.

Anyway, now I found a way to finally play this Activision classic again.

 

thanks for your support,

twh/f2

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