B-Em fault with Galaxy Raiders???

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Michael Brown
Posts: 1894
Joined: Sat Apr 03, 2010 12:54 pm
Location: Nottingham

B-Em fault with Galaxy Raiders???

Postby Michael Brown » Thu Feb 16, 2012 7:27 pm

Not sure if it is a fault but Galaxy Raiders by Visions hangs when loaded from the uef tape image on B-Em.
I may have mentioned this before in a different thread.

I have taken a look at my disk image from my Games Disk 8 which used elements from the uef tape image in the STH and this version works on BeebEm but not B-Em just like the tape image.

I find it very strange as B-Em is more close to a real beeb than BeebEm yet B-Em hangs the tape image. I have not had access to a real BBC to check if the tape image works fine or not, so therefore cannot tell if the problem is with the image or B-Em.

One thing I can now tell you is that I have got Galaxy Raiders to work on B-Em by altering the code at &1A30 (or &2A30 fro disk) which does a LDA #&80 to a LDA #&15.

I am not sure what basically a *FX 128,1 does but by changing it to *FX 15,1 the game now works fine and I have tested it this afternoon and have had no problems.

Therefore here is a special B-Em version of my Games Disk 8 with the change.

BBC Arcade Games Disc 008bem.zip
(133.42 KiB) Downloaded 108 times


I know a few people don't like the games being hacked, but this is currently the only way this game will work on the B-Em emulator.

If anyone can check the tape image on a real BBC and let me know then that would be great otherwise I wonder if Tom Walker has any ideas why B-Em does not like that code or maybe it is the BEQ routine after it.

regards,
Mick.

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MartinB
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Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity

Re: B-Em fault with Galaxy Raiders???

Postby MartinB » Thu Feb 16, 2012 8:51 pm

Works fine when loaded via UPCFS (~6s) :D

firthmj
Posts: 227
Joined: Tue May 26, 2009 8:37 am
Location: Ipswich, UK

Re: B-Em fault with Galaxy Raiders???

Postby firthmj » Thu Feb 16, 2012 8:57 pm

According to the BeebWiki, OSBYTE &80,1 should read the first A/D channel - the equivalent of ADVAL 1.

Presumably if you've changed A to &15, that's actually the equivalent of OSBYTE 21, not OSBYTE 15?

If so, you've basically changed it to a call to flush the serial input buffer

I guess a quick test would be to compare the ADVAL behaviour of B-Em, BeebEm and a real Beeb.

Regards

Michael
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Meeting 13th May 2017

SarahWalker
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Re: B-Em fault with Galaxy Raiders???

Postby SarahWalker » Thu Feb 16, 2012 9:01 pm

It's waiting for ADC channel 1 (joystick 1 X) low byte to go non-zero. No idea why. The existing emulation has the default midpoint being $8000 so this obviously doesn't happen.

Temporary solution - if you have a joystick plugged in, move it left-right a bit.

Michael Brown
Posts: 1894
Joined: Sat Apr 03, 2010 12:54 pm
Location: Nottingham

Re: B-Em fault with Galaxy Raiders???

Postby Michael Brown » Wed Mar 14, 2012 4:28 pm

It looks like this was the only game that did this. It does seem strange as to why it does this at the start.


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