Hydra-16

Hydra 16

A multitasking 65C02 computer and its operating system, HydraOS.

The Hydra-16's hardware gives each of 16 tasks its own 32K of RAM, zero page and stack included, with its own RAM and ROM bank selections, so a task switch is one register write. HydraOS runs on it, Plan 9's way:

• One kernel in the BIOS ROM: a preemptive scheduler, one interrupt path, notes, memory and banks, and a jump table made from a specification. Everything else is a module of the paged ROM, run in place in a task of its own.
• A base to build on: the kernel, a serial console driver, the kernel's devices and Woz's monitor are the base (base/), which HydraOS is built on and which boots on its own: write an OS of your own on it.
• Everything a file: devices are file servers (the console's windows, the disks and HydraFS, sound, GPIO and I2C, the clock, the Vera X, and /pc, a folder on the PC over the serial line), and each task has a namespace of its own, built by binds and mounts.
• Shells and languages: rc, Plan 9's shell, and the core tools; HyForth (Forth 2012), the login shell; hylang (danlang, a lisp); HyBASIC (QuickBASIC's kind, every number exact); SDKs for C (cc65) and assembly, and as, an assembler on the Hydra itself.
• Tools: a screen editor (edit), a debugger (db), a song player that plays ZSM songs and compiles scores as it plays.

The code is built with cc65 (https://cc65.github.io/), and the board is designed in KiCad 9 (https://www.kicad.org).

Quick start

cd base
node build.js                      the base alone: the kernel, ser, kdev, the monitor (bin/bios_*.bin, bin/prom0.bin)
node sim/run.js -i                 its monitor in your terminal (Ctrl-A x quits)

cd ../reborn
node build.js                      build HydraOS (needs Node.js and cc65): bin/bios_*.bin, bin/prom0.bin ...
node sim/run.js -i                 use the Hydra in your terminal, in the emulator (Ctrl-A x quits)
node sim/web.js                    the emulator in a browser: one file, bin/hydra-16.html, to open (in Git: no
                                   Node.js needed to use it)
node sim/test.js                   the regression tests

The ROM images are in Git (reborn/bin/) and on each GitHub release, so the chips can be programmed without a toolchain.

Documentation

The Hydra-16 book is everything, in order: what the machine is, the board and how to build it (the parts, the layout, the quirks), the kernel and its calls, the drivers, the shell, the languages, the tools, the emulator, and the programming guide. It's also one PDF, to print.

How it was designed, and where it stands: the plan and the design notes.

Repository