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Under the microscope: Aemulor
By Thom Holwerda, submitted by markee174 on 2018-05-13 15:37:43

After the release of the Iyonix PC in 2002, RISC OS started moving from 26-bit architecture towards 32-bit. Nowadays all modern RISC OS machines are 32-bit, but an awful lot of older applications are still not compatible with modern 32-bit RISC OS.

Aemulor, originally a commercial application but now free to download, is a software emulator that allows RISC OS applications which were written for a 26-bit ARM systems to be used on more recent CPUs that provide only 32-bit addressing modes. RISC OS itself is unaware that there is anything unusual about the 26-bit applications that are running under Aemulor, to RISC OS they appear as normal applications - they appear on the icon bar and can communicate fully with other 26 or 32-bit applications.

I've bought a Raspberry Pi 3 Model B+ just for RISC OS, so hopefully, I can start posting more about this old but venerable operating system in the future. Any tips or interesting things for me to investigate are welcome.

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Smp
By judgen on 2018-05-13 20:33:19
RISCOS can do smp now http://www.riscository.com/tag/s... all software needs a recompile though to be smp compatible on your pi. Hope you try it out.
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Nostalgia
By flypig on 2018-05-14 09:12:11
Aemular is an amazing piece of engineering, and I remember Adrian Lees, its author, running around one of the Acorn shows having got it working on the A9Home just hours after the release of the new machine.
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RiscLua
By GavinWraith on 2018-05-14 12:00:24
Good to see RISC OS mentioned in OS News. I have two
Raspberry Pi on my desk, a 3B running RISC OS (5.24)
and a 3B+ running Raspbian Stretch. When upgrades to
the Raspberry Pi appear, I use them with Raspbian first because, alas, RISC OS does not yet have the software to exploit the new features (multi-core, WiFi, Gigabit Ethernet, etc); then I upgrade the RISC OS machine with what the Raspbian one had previously - a sort of double-barrel pump action. I use Raspbian for browsing (with Chrome) but I prefer RISC OS for email (RComp's Messenger Pro and NetFetch) and for programming (RiscLua).

I have been banging on since 2002 about how well Lua's philosophy of minimalism is well suited for use under RISC OS, particularly as a modern replacement for BASIC. But I am afraid I have been a voice in the wilderness; nostalgia for BASIC is too strong and there are few people left in the
RISC OS community who are interested in, or perhaps even know of, the advantages of more modern programming languages. Until 2015 there was no way to use dynamic linking in RISC OS, so, upto that time, RiscLua had to be statically linked.
I took the opportunity to throw into the RiscLua pie
Roberto Ierusalimschy's amazing lpeg library (Lua Parser Expression Grammar). Now, with GCC 4.7.4, the standard Lua distribution can be compiled pretty much out of the box, and the Riscy part of RiscLua is provided as a shared object library. This gives access to RISC OS SWIs (software-interrupts), much as BASIC does, and I was careful to provide a syntax as close to BASIC's as possible, so as not to frighten the horses. So 'dim' and 'sys' in RiscLua play the role of 'DIM' and 'SYS' in BASIC; RiscLua provides notations ![x], ?[x] and $[x] which in BASIC would be !(x), ?(x) and $(x). But simple-minded transcriptions from BASIC to RiscLua are almost certainly mistaken because the two languages adopt fundamentally different strategies of interpretation.

Along with so many other users of RISC OS, I am getting a bit too old. I am hoping that younger, more energetic, people may develop things like RiscLua further, because there are all kinds
of interesting challenges: a really easy library for GUI programming, for a start. Lua's possibilities for high-level abstraction cry out to be exercised here. Because Lua is often used in bare-metal projects, it would be good to see it incorporated at a much lower level, with RISC OS built on top
of it, using its memory-management facilities. Then there is Lua-JIT, of course, ... .
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RISCOS has a closed source problem
By smoerk on 2018-05-15 17:14:28
at some point all the old guys will stop developing their closed source software and nobody will be interested to resurrect this stuff.

it will work another decade,…
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Will it work? :P
By zima on 2018-05-18 01:09:05
So Thom, will it work this time / with this RPi, did you already check it? :P (if not, I might be laughing even more from an emulated RISC OS machine ;) )

And to make this post more useful: some time ago I stumbled on a book Practical Raspberry Pi with some decent introductory RISC OS info: https://books.google.pl/books?id=... (I hope this links to page 208...)

BTW, I just love how in RISC OS the cursor shows if "wait for 2nd click" is still active when double-clicking. :)
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Why 26-bit?
By zima on 2018-05-18 21:50:01
PS. I always wondered / could anyone chim in, why older RISC OS machines used such "odd" bitness, 26? (or perhaps it's not odd at all, with 16 and 32 steps beeing just as arbitrary?)
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