Re: FinnOS Design Notes, was Re: FocusDrive and Interrupts

[David Schmenk <dschmenk@gmail.com>]

On Nov 3, 2:50 pm, dog_...@macgui.com (D Finnigan) wrote:
> D Finnigan wrote:
> > I'm going to write a blog entry tomorrow or the next day which will
> > incorporate my design notes and plans so far. I'll give a link to that
> when
> > it has been published.
>
> Design Notes of FinnOS:http://macgui.com/blogs/?e=358
>
> Hardware Documents for FinnOS:http://macgui.com/blogs/?e=359

You will definitely want Virtual ][ for development.  One thing to be
aware of is that IRQ's tend to confuse Virtual ][ when you bring up
the Inspector.  If an IRQ occurs while single stepping, you get stuck
in the interrupt handler code and it is hard to get back out.  This is
very frustrating when the interrupts are coming in at 60Hz.  Also, you
might want to look at your process priority scheme.  Usually, you will
only run the process of highest priority and round-robin those of
equal priority.  Most processes will do some sort of I/O and wait,
giving other, lower priority processes time to run.  If you start off
by using cooperative scheduling, you can get the system up and running
without adding the complexity of interrupts.  It will be much easier
to get working and debug (especially using Virtual ][), and you can
add pre-emptive scheduling in later without a great deal of effort
(although, believe me, interrupts and aux memory can drive you nuts).

Also, you should put a great deal of thought into the tools you want
to build the system with.  It doesn't have to be a technical decision,
either.  Sometimes part of the challenge is to use tools of the day
and develop directly on the Apple II.  However, modern tools can
vastly improve your productivity; if you don't have an excessive
amount of free time on your hands, that should be a consideration.
Don't under-estimate the complexity of your project, you may want to
"cheat" in some areas to give yourself a better chance for success.

Good luck, it sounds like a fun project.

Dave...