Date   : Mon, 01 Aug 2011 18:44:34 +0200
From   : rick@... (Rick Murray)
Subject: Risc PC (Was 'Minitel in France')

On 25/07/2011 23:49, Tom Walker wrote:

> Doesn't Aemulor do actual emulation?

Yikes! Isn't it easier to run sanitised code natively and trap things 
known to be problematic? Surely a full emulation would be... tedious?


> Win16 stuff runs natively, just with lots of 32->16->32 bit thunking.

...isn't the 16 bit environment the one that uses memory models, as to 
the 32 bit flat addressing space? It might be more complicated than 
running native. Not to mention Win16 is co-operative while Win32 is 
pre-emptive.


> I've heard there are actual technical reasons this hasn't been done,
> mainly interoperability between the Win16 and Win32 sides.

http://sourceforge.net/projects/portableubuntu/

If they can do *that*, they ought to be able to cope with this...


> that or MS just keep having nightmares about how the Win16 VM
> worked in OS/2 (ie badly).

I remember those days, but then hardware was a lot less advanced.


> I'd be impressed if you could do this with hardware that hasn't
> been released yet.

I'm talking about testing on current hardware, rather than "only the 
author's own". We can't talk about future hardware, it is impossible to 
predict. We just have to rely on the manufacturer not to arbitrarily 
change things and break everything.


> Methinks you're getting a bit confused here :)  I'm referring to the
> StrongARM R15 reading PC+12 in some circumstances when older chips
> read PC+8.

That's not really a change is R15, it's a side effect of the larger 
pipeline.


> but the SA 26-bit change was more subtle and also caused quite a
> few slip-ups.

I think the ARM6-StrongARM dual mode caused a few subtle issues with the 
exceptions in a 32 bit realm on a predominately 26 bit OS...


>> Aren't the early Beagles OMAP chips with ARM9 cores?
> No, Cortex-A8. Different beast altogether (Pentium to the ARM9's
> 486).

Ah, it must be the early OMAPs that were ARM926-based. I remember 
thinking it was amusing/ironic that the original OMAPs didn't seem that 
different to the TMS320DM320 in my PVR (a type of DaVinci, no?).


>> I dimly recall one of my machines (A5000?) having a small patch to
>> block writes from user mode to page zero. I think it was a couple
>> of lines of BASIC...
> Ah, but how much software worked afterwards? ;)

Most. You shouldn't be screwing around with page zero!


> I believe he was referring to OS_Heap changes.

<gulp!>

I wonder what changed.


Of course, on the other hand, think of the RMA and its supposed ability 
to maintain a sliding heap instead of a module area full 'o holes. I 
wonder, if the RMA was rejigged to be a sliding-heap, how much stuff 
would break...


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...