Found this of retro geek interest,

The Tube being not YouTube or a canned human transport system, but the
second processor connector, where then the Pi can pretend to be a 6502
SP, native ARM, or a 80286, and others ...

  Acorn BBC Master Raspberry Pi Co pro demo
  https://www.youtube.com/watch?v=mP7fiaync5E

http://www.sundby.com/index.php/pitubedirect-manual/

0 for the 65tube based 65C02 Co Processor @274MHz
1 for the 65tube based 6502 Co Processor @3MHz
2 for the lib6502 based 65C02 Co Processor @19.8MHz
4 for the Z80 Co Processor w CP/M bootstrap
8 for the 80286 Co Processor
9  for Acorn 6809 Co Processor
12 for the Acorn ARM2 Co Processor (Acorn)
13 for the Pandora 32000 Co Processor
14 To disable the Co Processor
15 for the native ARM1176 1GHz processor

--
Adrian C

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