Comment by digitalsushi
Comment by digitalsushi 2 days ago
Spock levels of fascinating from me. I want to learn how to compile a pdp11 emulator on my mac.
Comment by digitalsushi 2 days ago
Spock levels of fascinating from me. I want to learn how to compile a pdp11 emulator on my mac.
> After that, I've had great fun playing with RT-11 [...]
If you want to play around with RT-11 again, I made a small PDP-11/03 emulator + VT240 terminal emulator running in the browser. It's still incomplete, but you can play around with it here: https://lsi-11.unknown-tech.eu/ (source code: https://github.com/unknown-technologies/weblsi-11)
The PDP-11/03 emulator itself is good enough that it can run the RT-11 installer to create the disk image you see in the browser version. The VT240 emulator is good enough that the standalone Linux version can be used as terminal emulator for daily work. Once I have time, I plan to make a proper blog post describing how it all works / what the challenges were and post it as Show HN eventually.
The daves garage youtube has an episode where he documents the pitfalls of compiling 2bsd for a PDP-11/83. https://www.youtube.com/watch?v=IBFeM-sa2YY basically it is an art on a memory constrained system.
What I found entertaining was when he was explaining how to compile the kernel, I went Oh! that's where openbsd gets it from. it is still a very similar process.
On openbsd it's
cd /sys/arch/$(machine)/conf
cp GENERIC CUSTOM
vi CUSTOM # make your changes
config CUSTOM
cd ../compile/CUSTOM
make
I have never done it for 2bsd but according to http://www.vaxman.de/publications/bsd211_inst.pdf
cd /usr/src/sys/conf
cp GENERIC CUSTOM
vi CUSTOM
./config CUSTOM
cd /sys/CUSTOM
makeFrom the link:
> It's somewhat picky about the environment. So far, aap's PDP-11/20 emulator (https://github.com/aap/pdp11) is the only one capable of booting the kernel. SIMH and Ersatz-11 both hang before reaching the login prompt. This makes installation from the s1/s2 tapes difficult, as aap's emulator does not support the TC11. The intended installation process involves booting from s1 and restoring files from s2.
Apparently Yufeng got SIMH to run it: https://www.tuhs.org/pipermail/tuhs/2025-February/031427.htm...
So what mechanism do you have set up to reply 4 minutes after being mentioned? :)
What’s the difference between an emulator and a simulator in this context?
There is LOADS of gray area, overlap, and room for one's own philosophical interpretation... But typically simulators attempt to reproduce the details of how a particular machine worked for academic or engineering purposes, while emulators are concerned mainly with only getting the desired output. (Everything else being an implementation detail.)
E.g. since the MAME project considers itself living documentation of arcade hardware, it would be more properly classified as a simulator. While the goal of most other video game emulators is just to play the games.
I don't want to offend you , but this has made me even wonder more what the difference is.
It just feels that one is emulator if its philosophy is "it just works" and simulator if "well sit down kids I am going to give you proper documentation and how it was built back in my days"
but I wonder what that means for programs themselves...
I wonder if simulator==emulator is more truer than what javascript true conditions allow.
In theory, an emulator is oriented around producing a result (this may mean making acceptable compromises), whereas a simulator is oriented around inspection of state (this usually means being exact).
In practice the terms are often conflated.
The difference is about as crystal clear as compiler/interpreter.
Adding some anecdata, I feel like emulator is mainly used in the context of gaming, in which case they actually care a great deal about accurate reproduction (see: assembly bugs in N64 emulators that had to be reproduced in order to build TAS). I haven't seen it used much for old architectures; instead I'd call those virtual machines.
definitely agree on simulator though!
I think it is more about design, emulation mimics what something does. A simulator replicates what something does.
It is a tiny distinction, but generally I'd say that a simulator tries to accurately replicate what happens on an electrical level as good one can do.
While an emulator just does things as a black box ... input produces the expected output using whatever.
You could compare it to that an accurate simulator of a 74181 tries to do it by using AND/OR/NOT/... logic, but an emulator does it using "normal code".
In HDL you have a similar situation between structural, behavioral design ... structural is generally based on much more lower level logic (eg., AND/NOR/.. gates ...), and behavioral on higher logic (addition, subtraction ...).
"100%" accuracy can be achieved with both methods.
Yep, this is a metal-detectorists finding religious relic moment.
Have fun with that
https://hackaday.com/2017/01/03/make-logic-gates-out-of-almo...
Or you could go the way of this quite impressive project: http://fpgaretrocomputing.org/
Compiling an emulator is quite easy: have a look at simh. It's very portable and should just work out of the box.
Once you've got that working, try installing a 2.11BSD distribution. It's well-documented and came after a lot of the churn in early Unix. After that, I've had great fun playing with RT-11, to the point that I've actually written some small apps on it.