Date   : Mon, 20 Mar 2006 20:11:08 +0000
From   : Tom Seddon <tom@...>
Subject: Re: Advanced BASIC pretending to be the MOS!

Steve Fewell wrote:
> When Advanced BASIC starts, if it cannot detect the
> Tube, instead of printing a helpful 'No Tube' error
> message and exiting to the MOS, it goes into an
> endless loop of:
> Print *
> Input line - OSWORD 0
> Send line to MOS - OSCLI
> <deal with Escape condition>
> Loop
> 
> It also sets up the BRK vector so that it is handled
> by Advanced BASIC ROM code - so the language never
> exists not even on an error condition.
> 
> So the User thinks they are in the MOS - but arent!
> Why does it pretend to be the MOS? Because it can? Or
> because a language ROM is never supposed to exit
> (unless another language is activated) even if an
> error occurs?

I guess you might want to run the system exclusively as a Tube system, 
and not have original BASIC installed. But OS 1.20 doesn't supply any 
way of operating the computer without a valid language ROM; this way, 
if there's some kind of problem, you can at least attempt to diagnose 
the problem.

--Tom