AltPi-11

AltPi-11 is an alternate software implementation for the PiDP-11, an emulated PDP-11/70 running on the Raspberry Pi with a replica of the PDP-11/70 front panel, created by Oscar Vermeulen. The emulation is done by SimH, a suite that provides emulations for many historic computers, including the PDP-11 series. The PiDP-11 includes a software package that contains installation and start scripts, and a patched version of SimH that includes a "real console" device. That device uses Jörg Hoppe's Blinkenbone, a protocol used to connect real and virtual console devices to emulated computers.

Goals

The overall goal of this project is to make a lighter integration between the PiDP-11 and SimH. Point-by-point:

• Run with unmodified releases of SimH, without requiring patches or custom devices.
• Remove dependency on Blinkenbone, and specifically its dependency on SunRPC.
• Provide an architecture that will provide a path to support additional SBCs beyond the Raspberry Pi 3 and 4.

Status

• With used with Raspberry Pi 3, memory can be deposited and examined using the PiDP-11 panel. Programs entered using PiDP-11 switches run.
• SimH process is spawned, and some of the PiDP-11 lamps are illuminated based on the simulator state.
• Raspberry Pi 4: Not tested, but the driver for the Broadcom BCM2711 SoC is included.
• Raspberry Pi 5: Skeleton for the driver for the RP1 in place.

TODO

• Finish the console implementation as described in Section 3 of the KB-11C Processor Manual (PDP-11/70) (EK-KB11C-TM-001).
• Verify functionality on Raspberry Pi 4.
• Complete RP1 GPIO implementation for Raspberry Pi 5.
• Connect to console port and redirect to tty. ** This is how the SimH front panel support works; possibly provide upstream patch to change how this works.
• Parse ini file to find go and boot directives, and use the SimH front panel API to start execution.

Building

1. A few source files from SimH are required. Download a source release or use a local source control workspace with the SimH source.
2. Set the SIMH_SRC environment variable to the root of the SimH source tree. The default value is ../simh.
3. Run the build.sh script

Running

AltPi-11 requires the pdp11 binary from a SimH release. The pidp11 executable takes two arguments: the first is the path to the pdp11 binary from SimH. The second is the path to a SimH initialization file. Note, that file must not include "go" or "boot" directives, and it must include the configuration to move the console to telnet. For example

set cpu 11/70 4M
set console telnet=1030
set console telnet=unbuffered

Run:

pidp11 /path/to/pdp11 /path/to/ini

SimH will wait until a connection to the console has been made. Use the nc command to make that connection:

nc localhost 1030

The pidp11-off program can be used to turn off the lamps on the PiDP-11, if any are left on.

Acknowledgements

• Oscar Vermeulen: Creator of the PiDP-11 and other high-quality console replicas.
• Jörg Hoppe: Creator of Blinkenbone and the original software to connect the PiDP-11 to SimH.
• Bob Supnik: Creator of SimH.
• SimH Maintainers