Date   : Fri, 12 Aug 1994 09:16:02 +0100
From   : jfid@... (James Fidell)
Subject: Re: i see basic! :-)

Stephen Quan wrote:

> I am now ready to start implement the rest of the BBC, but don't
> know where to start.  Any pointers?  My first question is what does
> the real OSWRCH and OSRDCH do?  I suspect that I can let the real
> OSWRCH loose only when I have implemented some of the 6845, but
> without disassembling I am clueless on how OSRDCH might work.
> Does it just go into some kind of wait loop waiting for a keyboard
> interrupt???

Once BASIC is running and ready to go, I think it calls the OS to
read a line of text (using OSWORD ?).  This eventually ends up in a loop
waiting for something to be put in the keyboard buffer, I think.

The keyboard buffer is filled independently of this process by responses
to a keyboard interrupt.

> Another question.  The Advance User Guide gives a decent memory
> usage for the first couple of pages (my 1 page = 256 bytes).  Things
> such as the joystick, the system clock and so on.  When I get around
> to emulating those should I directly update these bytes or does some
> other ROM do that?  The 6522 perhaps?

Once you're hardware emulation is OK, you should not need to worry about
any of this -- it will all get done by the OS.

James.

-- 
 "Yield to temptation --             |
  it may not pass your way again"    |     jfid@...        
                                     |
        - Lazarus Long               |              James Fidell