Date   : Wed, 07 Aug 1996 11:12:47 +0100
From   : Ian Stephenson <ians@...>
Subject: Re: Introduction and 8bit newsgroup natter

>For example, I
>recently spent a while lurking in the comp.sys.cbm group
>where I
>heard about 3 Unix like operating systems and 1 Pre-emptive
>multitasking OS (yup, you read that right!)
>that are in development for the C64
Did it back in '88.

I used a sideways ram board which supported 8 banks as virtual memory for each  
process. The main ram held the main OS and workspace for IPC. On receiving a  
6522 interupt the OS would copy the stack, and selected zero page locations to  
elsewhere in main ram, and restore an old copy for the next process.

The main problem was with IO, as the real OS will re'enable interupts during  
operations so any real IO had to be done at the end of the time slice  
(shouldn't have been a problem, but I never quite got it right).

To be honest the main problem was that I was learning about operating systems  
- I'd read a book on Unix, and was figuring out how to build a multi-tasking  
OS. Hence there are a lot of mistakes, but a lot of good stuff too. Were I  
doing it again (or just developing ti further) ot could be a fully funcitonal  
environment.

A few years back I also started work on a CP/M/DOS like environment for the  
6502 co-processor. Basically I wanted to be able to run commands from disk,  
recursivly and have a real shell. As part of this I ported BCPL. As with the  
previous project it never quiet got all the problems ironed out.

You might also like to look at the Oric groups - they've done a lot of work on  
getting C working. Their work is based on a BBC port of lcc that I did.  
They've taken it a lot further than anyone was interested in on the BBC.

$an