SoCDP8      

This is an implementation of the 1968 DEC PDP-8/I on <br> a Xilinx Zynq, a FPGA controller with an ARM CPU.

Built on the PiDP-8/I Console by Oscar Vermeulen, <br> it acts as a replacement for the Raspberry Pi approach.

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Why a SoC?

Drawback of the Raspberry Pi + Linux + SIMH approach:

• Inaccurate Simulation : Doesn't allow for single stepping
• Long Boot Times : Linux takes a few seconds to boot and start SIMH
• Dangerous Shutdown : In the default Raspberry Pi setup, Linux needs a proper shutdown to avoid corrupting the file system

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The SoCDP8 implements the PDP-8/I in VHDL, targeting FPGAs.

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Design

The system is modeled exactly as described in the <br> Maintenance Manual and Engineering Drawings.

The manual is treated as the project specification, registers <br> and signals are named as described in the book and register <br> transfers are modeled as specified in the drawings.

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Peripherals

Peripherals are implemented on the ARM CPU on the SoC.

This makes device implementation such as the teletype fairly easy.

Code for peripherals can access the onboard <br> SD Card to retrieve tapes, disk images, ..

When connected to the Ethernet / WiFi, the system, including <br> its peripherals, can be controlled with a Web Browser.

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Project Goals

• Implementing the system as close as possible to the original specifications.

• Providing a simple replacement for the Raspberry Pi, <br> ideally the project runs on a SoC board that snaps into <br> the PiDP-8/I Console in the same way the Pi does.

• Have it be operable through a browser using <br> a web socket connection between a web server <br> on the ARM and the PDP-8 on the FPGA.

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Supported SoCs

The project currently only targets the Zynq board <br> and utilizes the Pynq-Z2 for development only.

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Tested Boards

| Board | | |:-----:|:-| | ZynqBerry | <br> Xilinx Zynq 7010 <br><br> - 130€ | Good Availability <br><br> - Raspberry Pi form factor <br><br> - No free GPIO pins <br><br> - Has the smallest Zynq <br><br> | | Pynq-Z2 | <br> Xilinx Zynq 7020 <br><br> 132€ | Good Availability <br><br> - Raspberry Pi Connectors <br><br> - Spare GPIO pins, such as a <br><br>  PMOD pin, useful for sensors<br> - Switches, buttons, LEDs <br><br> - Requires a ribbon cable to <br>  fit in the PiDP-8/I box <br><br> |

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Other Boards

| Board | | |:-----:|:-| | DE0-Nano-SoC | <br> Altera Cyclone V <br><br> - 125€ | International Shipping <br><br> - Incompatible 40 pin connector, <br><br>  requires adapter. <br><br> - Many free GPIO pins <br><br> - Switches, buttons, LEDs <br><br> |

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Project Status

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Functional

• Base System
• Timesharing
• Data Breaks
• Interrupts
• EAE
• I/O

These features pass the MAINDEC tests and <br> can be loaded using the RIM / BIN loaders. <br> <br>

Can Run

• Focal69
• TSS/8
• OS/8

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Peripherals

Implemented in software with only basic functionality.

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Deviations

To have the PiDP-8/I work with the Zynq boards, <br> unfortunately a little modification had to be made.

The 1KΩ resistors had to be replaced by 220Ω ones <br> to support the pullup resistance of the Zynq drivers.

Thankfully, 220Ω is compatible with the Raspberry Pi as well so these resistors also support the original system.

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