RISC OS IA-32!

It is known that x86 instructions are microcoded. It is also known that the microcode is interpreted by a fast RISC processor. What is not generally known is that the RISC core is actually a variant ARM processor. Following Intel’s development work for the XScale processor, it was realised that the ARM core was substantially suitable for running at high speeds to work as the back end of x86 architecture CISC processing units.
The first Intel x86 processor to incorporate the ARM core is the 7th generation Pentium 4 “Prescott”, which was a major reworking of the Pentium 3 “Heseltine” that was never commercialised due to continuing problems with the floating point unit. All of the straight 32 bit processors since then incorporate an ARM core.

Now, thanks to the Chinese company “Bèndàn Èzuòjù Group” (a company that essentially specialises in chip-stripping and cloning), they have uncovered a way to switch out of x86 mode and in to ARM mode.

A specially constructed data table needs to be created, and ES:EDI set to point to it.
Instruction 0Fh 07h is then executed. This instruction loads the entire processor state from the data table provided (taking 51 cycles), and as a side effect, will have switched the processor to ARM mode by disengaging the x86 translator.
And with that, it is possible to run RISC OS.

There are several caveats – all interrupts (software or hardware, and vectors (abort, etc)) will automatically switch the processor back to x86 mode. Only one core can be used at a time – the x86 translator works for all cores however the state of the processor (ARM or x86) is only available to the core that is set to handle the interrupt/vector. The other cores will change state as the translator is re-enabled for all cores with no notification. This eccentricity of design precludes the ability to use multiple cores in ARM mode. The handlers for the interrupt and vector conditions will then need to deal with the issue (as an x86) and then switch back to ARM mode. It is not currently believed to be possible to create a reentrant handler that switches to ARM mode immediately, as the x86 does not appear to switch to x86 mode while it believes it is in the handler. The necessity to switch back and forth does cause a lag, but on a 2.6GHz processor, the speed is judged to be “acceptable” (about as fast as a RaspberryPi), however the actual speed depends upon the number of interrupts – USB transfers (especially USB networking) really hammers it. Expect networking in this manner to be slow. There may also be issues with missing or repeated keypresses, though these are expected to be ironed out in time due to further developments of the x86 handlers.

For those with a suitable x86 32 system (sorry, the specifics of the IA64 core are not currently known), a bootable CD image of RISC OS 5.19 may be downloaded from http://www.riscos-ia32.cn/ and I expect the (somewhat old) version of RISC OS to be updated in the following weeks.

You lot are no fun!
This sounds really exciting, I look for an update this time next year!
And thanks for “finding” this gem.

All of the straight 32 bit processors since then incorporate an ARM core.

ah youth.

The tradition is for pre-12 noon shipment of such missives otherwise they are returned to sender. I suppose it is pre-noon in Hawaii.

The tradition is that you land your “Peche” before Noon!

The company also trades under the following name on alibaba IIRC:

Now, thanks to the Chinese company “Bèndàn Èzuòjù Group” (a company that essentially specialises in chip-stripping and cloning), they have uncovered a way to switch out of x86 mode and in to ARM mode.

Rick – the poisson d’avril finishes at midday! Fish pie for you tonight!

As a non-morning person (and having gone to work this morning anyway) I tend to ignore the noon rule¹. :-)

¹ Which I feel was instigated by a British² person with no sense of humour so they could get back to their scheduled boredom.

² The noon rule is of British origin. [source]

A bit late in the day but one of the best I’ve seen today:-)

As a non-morning person

Just like Des Cartes, who did not like to rise before 3 o’clock in the afternoon. I suppose you have all seen Riscository’s ( http://www.riscository.com/ ) Breaking news?

I suppose you have all seen Riscository’s Breaking news?

Yeah, well, you’re laughing now.

We were all laughing, once. Spooks were like Mulder, right? Then this bloke called Snowden came along…
We aren’t laughing any more.

The noon rule is of British origin. [source]

There has to be rules.
Of course in France the done thing is to agree the rules and do something different :)