openmipsx

Open tools for MIPS-X, the 1980s Stanford RISC design that ESS Technology built into its ES38xx media chips. The main target is the ES3890F, the processor in the Sipura and Linksys SPA and PAP2T analogue telephone adapters. MIPS-X is not the commercial MIPS architecture, and no mainstream compiler supports it. So the project builds a compiler, C library, simulator and analysis tools for it, and uses them to write open replacement firmware for those adapters.

Early days

This site has only just started. Until its pages are written, the links below go to the documents in the project's repositories.

Where things stand

Milestone	Status
Toolchain: Clang, lld, picolibc and a simulator	Working on the simulator; first release in preparation
First image of our own on a board	Done, 2026-11-02: an LED blinker ran on an SPA3000
Kernel: timer interrupt and task switching	Next
Network: Ethernet driver, TCP/IP, DHCP	To do
Phone port: ringing, hook detection, dial tone	To do
SIP calls between the phone and the network	To do

Four ways in

Understand it

How these devices work, and why the project uses a clean room.

Devices · The clean room

Try it

Compile C for MIPS-X and run it on the simulator. No hardware needed.

Toolchain

Do a task

Build an image, flash a board, or recover one.

Start here

Look something up

The specs of the hardware, firmware image format and processor.

Specifications