Re: A89: Keyboard buffer

To: <assembly-89@lists.ticalc.org>
Subject: Re: A89: Keyboard buffer
From: "Scott Noveck" <noveck@pluto.njcc.com>
Date: Thu, 30 Sep 1999 16:25:52 -0400
Cc: <pizzaofhut@geocities.com>
Reply-To: assembly-89@lists.ticalc.org


>Hello everyone. I'm new to 68k programming, and was wondering if any of
>you could tell me where to find information specific on developing for
>the 89. BTW, I'm currently starting work on Metroid 89, and I need to
>know where the keyboard buffer on the 89 is and what the bra instruction
>does. Thanx.

I highly recommend against starting on anything even remotely close to
Metroid unless you have a good bit of assembly programming experience and
have worked with the 68k before -- it's how we all start, but those programs
are never finished.  I recommend something more tile-based to start with, as
side scrollers get very tricky and have to be well optimized.

The information you need on the keyboard buffer is included with the doors
zip (at least the developer version) in either ports.txt or one of the other
text files.

bra is the rough equivalent of GOTO in high-level languages.  While most
programmers hate GOTO - usually a poor command that can be used better with
a loop or large IF statement - it's necessary in ASM.  bsr is roughly like
GOSUB in BASIC (kind of like calling a user-written function in C), and lets
you return back to the command that called it.  bra is a permanent jump that
cannot be returned from.  the other bXX commands are a mixture of IF/GOTOs,
which only jump on certain conditions.  dbXX is similar but automatically
decriments the register and is very useful in loops.

    -Scott