While we're at it then... Ray asked for RT-11, since he felt that it was
smaller and simpler than most other operating systems available, and
also because he felt more comfortable with assembler than some other
language.
Both those points are missed with any Unix-like OS, even if the
intention is good.
I could just as well offer up RSX, since it actually comes with source
where the comments are still in place, and it's actually written in
assembler for the most part as well. However, it is a much more complex
system than RT-11, and in some ways probably more complex than Unix as
well. So I don't think it might be a good choice if you just want to
understand how an OS works.
In fact, I would probably suggest Ray start with just writing some code
to do some simple things without looking at existing code. The first
thing needed would be to just have something that can load programs from
a device, and run them. This will require some simple device driver,
some simple file system, and a simple command line interpreter. Then you
can go on an expand from there. You'll soon realize things you want to
abstract away, and deal with in a somewhat coherent way.
I wouldn't bother with interrupt system, MMU, or any more fancy stuff to
start with. A plain 64K PDP-11, with the program loader just located in
one end, and then go from there. Do system calls through TRAP, EMT or
some other instruction, and then have a vector installed. If the user
program overwrites that, tough luck.
Johnny
On 2016-10-23 02:45, Nelson H. F. Beebe wrote:
Ray Jewhurst <raywjewhu...@gmail.com> asks today for documented
operating system source code for the PDP-11. Besides the Lions' Unix
v6 code, there is also Doug Comer's Xinu project about which he wrote
several books. Current versions are targeted at x86 and ARM CPUs,
http://www.xinu.cs.purdue.edu/
but he still provides code for older systems (PDP-11, SPARC, VAX):
ftp://ftp.cs.purdue.edu/pub/comer/
There is more about him here, including links to his books Web site:
https://en.wikipedia.org/wiki/Douglas_Comer
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|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
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