Date   : Sat, 20 Nov 2010 21:57:50 +0000 (GMT)
From   : kranser@... (Steve Fewell)
Subject: BBC file formats

--- On Fri, 19/11/10, Michael Firth <mfirth@...> wrote:
> What he said :-)
> 
> Plus, the reason it can be done is that games usually have
> a startup 
> screen in Mode 7, which only needs 1K of RAM
> (HIMEM=&7C00), but run the 
> actual game in one of the high graphics and colour modes
> (usually Mode 1 
> or Mode 2), which need 20K of RAM (HIMEM=&3000).
> 
> Thus, with DFS you load the game above PAGE while in Mode
> 7, then switch 
> to TAPE, move the code down, and then you can switch to the
> high memory 
> mode.

Thanks for the detail Michael.

The simple loop to move the code down in memory doesn't do any address translation
for JSR/JMP - so I presume that the code was developed to run at &E00 (using O%)?

So, this begs the question as to how the programmer(s) tested the work, seeing
that they would need DISC access and the code would need to run at &E00 and
use a high-memory requirement MODE. So any ideas on how they would test the
Machine Code program?
I guess they would run the source BASIC program to create the machine code
on disk and then transfer the disk to another machine to run the machine
code, and then transfer the disk back to update and save the source program!

Kranser.