RiscPC Second CPU slot ARM possible?

Arc/RPCs, peripherals, RISCOS operating system & ARM kit eg GP2x, BeagleBoard
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sbadger
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RiscPC Second CPU slot ARM possible?

Post by sbadger » Wed Apr 18, 2018 1:04 pm

Hi there,

I've recently I've finally managed to update my 610 for a 710, just to give a bit more, (StrongARM out of budget and OS ROM version out of reach at the moment.!).
I've got a 486 in the second slot at the moment, but is it possible to put my 610 in the second slot? If it's even possible is there any software?

stew
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RobC
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Re: RiscPC Second CPU slot ARM possible?

Post by RobC » Wed Apr 18, 2018 2:10 pm

I think I read somewhere that the two processor slots are electrically identical so one of the CPU cards needs arbitration logic to allow more than one to run side-by-side. The x86 cards have this logic but the ARM ones don't :(

Somewhere, I have an "ARM Switcher" which allowed two ARM cards to be plugged into the same slot. As the name implies, it was designed to allow you to mechanically switch between the StrongARM and ARM710/610 when StrongARM software compatibility was an issue. I didn't use it much as it seemed unreliable and the software I was using soon gained compatibility.

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Re: RiscPC Second CPU slot ARM possible?

Post by sbadger » Sun Apr 22, 2018 6:22 pm

thanks Rob.
Personally I feel this is probably another trick missed by Acorn, though do understand it was all a bit before the true multi-threaded era.
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Re: RiscPC Second CPU slot ARM possible?

Post by flibble » Sun Apr 22, 2018 10:27 pm

The 'first ever' risc pc second processor was an ARM. Used internally inside Acorn to test the bus mastering, one of them is now at the CCH in Cambridge, via the Chris's Acorns collection.

http://chrisacorns.computinghistory.org ... dProc.html

This of course was not a general purpose board for accelerating regular risc os, just testing parts of the system before bolting an x86 on.

Edit: I should also add that you cannot put a regular risc pc arm processor in the second slot and have it work, it's missing some of the circuitry needed.

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Re: RiscPC Second CPU slot ARM possible?

Post by atcurtis » Fri May 04, 2018 11:33 am

flibble wrote:The 'first ever' risc pc second processor was an ARM. Used internally inside Acorn to test the bus mastering, one of them is now at the CCH in Cambridge, via the Chris's Acorns collection.

http://chrisacorns.computinghistory.org ... dProc.html

This of course was not a general purpose board for accelerating regular risc os, just testing parts of the system before bolting an x86 on.

Edit: I should also add that you cannot put a regular risc pc arm processor in the second slot and have it work, it's missing some of the circuitry needed.
Seems like with the included VHDL in the datasheet, someone may be able to craft an adaptor board which could turn a processor board into a co-processor board...

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Re: RiscPC Second CPU slot ARM possible?

Post by geraldholdsworth » Fri May 04, 2018 12:18 pm

I find it odd that Acorn never designed it so you could add a second ARM processor in that slot in the first place. After all, you could get a co-pro for the BBC, so why not the RiscPC?
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Re: RiscPC Second CPU slot ARM possible?

Post by BigEd » Fri May 04, 2018 12:37 pm

I suppose the cooperation which the x86 copro performs must be well-enough understood these days, so any copro which played by the same rules would be able to share memory and screen with the host OS?

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Re: RiscPC Second CPU slot ARM possible?

Post by davidb » Fri May 04, 2018 12:40 pm

Maybe the primary motivation was compatibility with other CPU architectures, so having a second ARM wasn't a design goal?

Let's imagine what might have happened if ARM second processors were available with the current design. From a product support perspective it would have been confusing for users to have two different kinds of CPU card. It makes me wonder whether it would have been possible to have a design that allowed primary CPU cards to be plugged into the second slot using an adaptor.

Now that clever people on here have mastered making second processors for the Beeb's Tube interface, maybe they can have a go at making second CPU cards for the RiscPC. ;)

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Re: RiscPC Second CPU slot ARM possible?

Post by RobC » Fri May 04, 2018 2:11 pm

geraldholdsworth wrote:I find it odd that Acorn never designed it so you could add a second ARM processor in that slot in the first place. After all, you could get a co-pro for the BBC, so why not the RiscPC?
The StrongARM effectively killed off the Hydra multi-processor board so maybe it also killed any notions Acorn had around dual-ARM machines?

When I bought my first RiscPC in 1996, it had 9MB of memory and an ARM710 running at 40MHz. A year later, I upgraded it to a 200MHz StrongARM and 66MB which made it much more powerful than I'd ever expected it to be when I bought it. This was a bigger jump in relative performance than adding a 6502 co-pro to a Master 128 in the late eighties.

I don't know whether there would be much benefit in running two StrongARMs given that the memory bus was only really designed with the ARM610, ARM710 and possibly the ARM8 in mind and it's often cited as a bottleneck when using one StrongARM.

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