Reverse Tube - an amusing idea

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crj
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Reverse Tube - an amusing idea

Post by crj » Sat Apr 07, 2018 3:28 pm

A random idea that occurred to me...

Tube ULA: 8 bytes of memory-mapped I/O
Tube space in SHEILA on the Beeb: 32 bytes

The logic required to connect a Tube ULA's host side to one Beeb normally, and the parasite side to &FEF0-7 on a second Beeb would be small and simple. (For added style, you'd include a follow-on port so the parasite Beeb could in turn have a second processor.)

Then take the Tube Operating System and adapt it into a sideways ROM for the parasite. Result: one Beeb able to use any and all of the peripherals of another, without any hardware or software modification to the latter.

Nowadays, I fear spare Tube ULAs may be a bit thin on the ground, but I'm quite surprised nobody did this back in the day. (Or, if they did, that I never heard of it.)

Admittedly, the kind of person who wanted to be able to run their video games from disc keeping PAGE at &E00 in 1983 probably wasn't the kind of person who could afford an entire second BBC Micro, but still. (-8

Coeus
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Re: Reverse Tube - an amusing idea

Post by Coeus » Sat Apr 07, 2018 6:38 pm

Were tube ULAs available as separate parts back in the day? They were fitted to the second processors, not the BBCs.

These days a BBC B may be cheaper than a second processor 6502 but was that the case back in the day? I would have hoped not.

Then there's the fact that a limit amount of parallel processing was only part of the reason to have a 2nd processor. Having an address space that can be completely devoted to RAM with a much higher proportion of it available for user programs/data was also important. You could get close to that these days if you fitted one of Chris Morley's OS RAM modules. That would enable the tube code for a parasite to run high in RAM where it would usually be, sideways RAM could host the language ROM copied across and you'd be free to use the screenb memory as you don't care what's on the video output you're not using.

It's a novel idea but PiTubeDirect would be cheaper.

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ask_nz
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Re: Reverse Tube - an amusing idea

Post by ask_nz » Sat Apr 07, 2018 10:12 pm

Ha ha - this is really amusing because I was having the same thought last week - ie. reversing the architecture and treating the co-processor as a true sub-processor. Worth a thought but I suspect the OS would have to be re-written to some extent.
Ade

crj
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Re: Reverse Tube - an amusing idea

Post by crj » Sun Apr 08, 2018 1:43 am

Coeus wrote:Then there's the fact that a limit amount of parallel processing was only part of the reason to have a 2nd processor. ...
This idea isn't a way to get the normal benefits of a second processor. People who want that can indeed use a normal second processor or, nowadays, PiTubeDirect.

What I'm thinking is that if you have two Beeb's wired up Tube-to-Tube then you can take a mix and match approach to which resources you use from each. The motivating example was to do most stuff on machine A, but have it use the filing systems from machine B so it can keep PAGE at &E00. (Since Machine A is still driving its own video, it can run all the software that chokes if asked to run in a normal second processor.) Or you could use both the 5.25" drives on one machine and the 3.5" ones on the other.

Sillier uses include getting stereo six-channel music, doubling up on serial and user ports, etc.

As I say, it's not really something useful enough that people would have easily justified the expense, I'm just amused that it looks like it would actually have been feasible!

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myelin
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Re: Reverse Tube - an amusing idea

Post by myelin » Sun Apr 08, 2018 1:57 am

crj wrote:The motivating example was to do most stuff on machine A, but have it use the filing systems from machine B so it can keep PAGE at &E00.
Ah, I see -- basically HostFS, except using the actual Tube protocol! (HostFS uses a modified version of the protocol so it can run over a serial port.)
SW/EE from New Zealand, now in Mountain View, CA, making BBC/Electron hardware projects for fun.
Most popular: fast serial port, FX2+PiTubeDirect Tube/Cartridge adapter, USB cart interface.

SteveBagley
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Re: Reverse Tube - an amusing idea

Post by SteveBagley » Sun Apr 08, 2018 7:55 am

myelin wrote:
crj wrote:The motivating example was to do most stuff on machine A, but have it use the filing systems from machine B so it can keep PAGE at &E00.
Ah, I see -- basically HostFS, except using the actual Tube protocol! (HostFS uses a modified version of the protocol so it can run over a serial port.)
Acorn had a HostFS podule that contained a ULA during development of the Arc to allow use of the BBC's drives — there’s a schematic and dump of the ROMs on here somewhere.

Here we go… http://www.stardot.org.uk/forums/viewto ... f=3&t=4472

Steve

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tricky
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Re: Reverse Tube - an amusing idea

Post by tricky » Sun Apr 08, 2018 9:05 am

crj wrote:...Sillier uses include getting stereo six-channel music, doubling up on serial and user ports, etc...
And stereoscopic 3D graphics although you might need some sort of sideways periscope for one eye if you are using two CIBs :lol:

crj
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Re: Reverse Tube - an amusing idea

Post by crj » Sun Apr 08, 2018 10:34 pm

...

!

Oculus Rift attached to two Beebs. Make one of them a Master; run a mashup of the Tube and Master versions of Elite, so it renders stereoscopically across both machines. If it worked, that would be easily the most awesomely preposterous abuse of retrocomputing I've ever encountered.

crj
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Re: Reverse Tube - an amusing idea

Post by crj » Sun Apr 08, 2018 10:38 pm

SteveBagley wrote:Acorn had a HostFS podule that contained a ULA during development of the Arc to allow use of the BBC's drives — there’s a schematic and dump of the ROMs on here somewhere.
Mmm. And between the Springboard and the Archimedes with the Tube Podule, there was the "A500 Second Processor".

I donated an A500 Second Processor (alas, missing its ceramic IOC, as I recall) to the National Museum of Computing in Bletchley Park. My memory is hazy, but I think a Tube Podule was in there somewhere, too.

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