PiTubeDirect allows a Raspberry Pi to interface to the Tube interface on a BBC Model B, Master, or Electron, and emulate a range of architectures as a Tube-attached second processor.
The host computer is able to select different emulations by writing to specific
locations across the Tube. This can be done with *FX commands (e.g. *FX 151,230,12 to emulate an ARM2), but since it is a bit hard to remember a bunch
of numeric arguments and what all of them do, I wrote a *PiTube command to
provide an easier-to-remember way to control PiTubeDirect.
*PiTube always runs on the IO processor, so it can be used with Second
Processor emulations of any instruction set, not just the 6502.
*PiTube
Shows an overview of valid commands.
*PiTube <processor> [option] [option]...
Selects a Second Processor with a given set of options.
Processor names and options are case-insensitive.
Processor selection will only take effect after resetting the system with
Control-BREAK. Note that this selection will not persist after the power has
been turned off - on initial boot, PiTubeDirect will always start with the
configuration defined on its SD card in cmdline.txt.
| Processor | Aliases | Options | Comments |
|---|---|---|---|
| 65C02 | 6502 | FAST, L6502 |
Standard 6502 Second Processor |
| 65C102 | 65102 | FAST |
Master Turbo Second Processor |
| Z80 | |||
| 80286 | 286 | Master 512 Second Processor | |
| 6809 | |||
| PDP11 | |||
| ARM2 | ARM | Acorn ARM Evaluation System | |
| 32016 | |||
| NATIVE | PI | Native Raspberry PI ARM6 or ARM7 | |
| OFF | Disable PiTubeDirect |
See the PiTubeDirect project page for further documentation about these processors.
NOTE: After selecting *PiTube OFF (or the equivalent *FX 151,230,16),
PiTubeDirect stops listening to the Tube, and another Second Processor cannot be
selected until the system has been power-cycled.
An less drastic alternative is available on BBC Master series machines:
*CONFIGURE NoTube (followed by Control-BREAK) disables the Tube interface in
software. The Tube interface can be re-enabled without power cycling with
*CONFIGURE Tube.
By default, the 65C02 and 65C102 processor emulations are calibrated to run at
approximately the same speed as the original hardware. The FAST option allows
the emulation to free-run at the highest possible speed, increasing performance
at the cost of potential compatibility issues.
The 65C02 processor emulation can use either the default 65Tube implementation,
or the lib6502 emulator core. Supply the L6502 option to select the lib6502
core.
*PiTube is written in BeebASM assembler; the distribution disc image can be
built with beebasm -i pitube.6502 -do PiTube.ssd.
The source is designed to be easy to add new processor types and options to, without having to modify the core logic. Adding a new processor should just be a matter of adding a table entry for it (and any desired aliases), and adding a function to parse and act upon any options that it may require.
- PiTubeDirect on GitHub: https://github.com/hoglet67/PiTubeDirect
- Similar tool, but menu-based: https://stardot.org.uk/forums/viewtopic.php?f=2&t=19647