Re: [stella] F4/F6/F8 Bankswitching

Subject: Re: [stella] F4/F6/F8 Bankswitching
From: Thomas Jentzsch <tjentzsch@xxxxxx>
Date: Sun, 15 Jun 2003 18:49:14 +0200
Aaron Bergstrom wrote:
> But I'm not clear on how the ASM file is to be structured so that each
> bank has an address of $1000 to $1FF3.

That's no problem, because due to addressing space limitations of the
6507, e.g. $1000 = $3000 = $5000...

You must logical ORG your banks at an odd 4K segment (else you might
access the TIA, RAM etc.)

E.g. ORG $1000 for the first bank and $3000 for the second bank works
good. But some standard is to use the last possible addresses, so you
should use $d000 and $f000 for 8K games.

Now it get's a bit more complicated:
The examples about would create 12K instead of 8K files, because you
skip the $2000 or $e000 bank and the assembler will fill that with $FF.

But there is RORG. This one is getting important for bankswitched games,
because it's only a logical origin and not a also physical one.

So your banks could start e.g. like this:
  ORG $1000
  RORG $d000
  ORG $2000
  RORG $f000

Note that you *always* must use ORG and RORG then.

Now all you code is assembled for the logical origin, but stored at the
physical one and you get a 8K file.

Have fun!
Thomas Jentzsch         | *** Every bit is sacred ! ***
tjentzsch at web dot de |

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