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Date   : Sat, 02 Feb 2013 17:09:11 +0000
From   : jgh@... (J.G.Harston)
Subject: Commodore 64 BBC BASIC

Today's update:
    http://mdfs.net/BBCBasic/C64

Worked out how to switch the running Kernal so the full 64K RAM is 
paged in, and BASIC can live in high memory _on_top_of_ the Kernal. This 
was a bit fiddly.

Calls to the Kernal are easy enough, wrap them in (save ROM bank), 
(select Kernal ROM), call Kernal, (restore ROM bank) - just like calling 
code in a BBC sideways ROM. The fiddly bit was doing this on the 
interrupts as well, as the stack structure is different for an IRQ/BRK 
than it is for a JSR, so you can't just JSR to the default code, you 
need to construct the correct stack contents and then jump to it.

Now I've got this working, it's decided the memory layout I'm going to 
use, so I can now sit down and fill in the rest of the Kernal interface 
veneer.

-- 
J.G.Harston - jgh@...      - mdfs.net
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