numini

A small CPU and a computer built around it.

Overview

Currently, the planned hardware is based around an iCEBreaker and an Inkplate 6. The original Inkplate 6 case's top is used (since the Inkplate came glued to it), but the bottom is replaced by a 3D-printed custom case that leaves room for the remainder of the components and ports on the bottom. The Inkplate provides power via a lithium battery, and access to its display, its microSD card, and its Wi-Fi and Bluetooth connectivity. The iCEBreaker is connected to the Inkplate over UART. The iCEBreaker is augmented with a quad HyperRAM PMOD module, which it uses for main memory. A CH559 is used to provide support for USB keyboards. It connects to the iCEBreaker over UART, essentially acting as a PS/2 keyboard would. Finally, a variety of devices connect to the iCEBreaker over I²C, including several MCP23017

The different components are in the following subdirectories:

case/ contains the OpenSCAD code for the case design.
ch559/ contains the source code to the Forth implementation that runs on the CH559.
fpga/ contains the Bluespec code that runs on the iCEBreaker.
inkplate/ contains the code that runs on the Inkplate.
simhost/ contains Rust code that implements simulated peripherals for bluesim.

CH559 Code

The CH559 is a microcontroller based on an enhanced 8051. It has two USB ports that can operate in device or host mode, which we will use to access USB keyboards. Programming the board is somewhat annoying -- it has ICSP support, but entering the programming mode requires unplugging the board's power. To circumvent this, and for general ease of development, the software for the board will be written in a custom Forth. The Forth implementation itself is in the ch559/ directory. To reduce reliance on external tools, an assembly toolchain is implemented in Python, and the Forth is implemented in that.

Inkplate

The Inkplate 6 provides 800x600 pixels with 3 bits of greyscale color depth. It quotes a 1.26s update time; in order to update at faster than the refresh rate, we need to run the UART at 2MHz, which gives a 900ms access time to send the whole framebuffer, or 1.2s if we send 4 bits per pixel.