Date   : Tue, 31 Jan 2017 13:18:39 +0000
From   : percy.p.person@... (Ed Spittles)
Subject: Pi-based second processor - fast, flexible, inexpensive

For the price of a Raspberry Pi and a level converter, you can now have a
second processor solution for your Beeb or Master. The setup can be small
enough to fit underneath the Beeb in the recess by the Tube connector, or
it can be fitted inside a Master. It can be powered directly over the Tube
connecter.

The project home page is
https://github.com/hoglet67/PiTubeDirect/wiki

The Pi can run as a 6502 model running at 3MHz or 274MHz equivalent, a Z80
at 60MHz, an 80286, a 6809, an ARM2 (at about 9MHz equivalent), a 32016, or
a gigahertz ARM7. You can choose which one it boots as, or switch using a
*FX command.

You can build your own level converter - only two chips needed - or use
John's Tube Silencer, or buy the Pi-specific one by Kjell. Overall, you
might pay
- ?4 for a Pi Zero, plus postage
- ?34 for a ready-assembled level converter and micro SD Card, inclusive of
postage.
(Many other combinations are possible - you might already have a Pi, or a
suitable SD Card. You might be happy to buy a kit and assemble your own
level converter.)

Note that the Pi Zero comes with a pin header which must be soldered on.
Other Pi models are ready to use, but are too large to fit under the Beeb.
(An IDE cable can be used to put the Pi next to the Beeb.)

Credit goes to Dave and to Dominic for making this project, and to many
others for assistance, feedback, and upstream open source projects.

The StarDot discussion thread is
http://www.stardot.org.uk/forums/viewtopic.php?f=3&t=11325

Kjell's level converter supply thread is
http://www.stardot.org.uk/forums/viewtopic.php?f=8&t=11761

John's Tube Silencer page is
http://www.zeridajh.org/hardware/tubesilencer/index.htm

(There is not presently a PDP-11 model...)