Implementations

Several implementations of the OpenRISC architecture exist. In the following we will summarize the most well known.

Hardware Implementations

The hardware implementations are full processor implementations written in an Hardware Description Language. Such a description is either the input to a hardware synthesis, such as for an ASIC or an FPGA, or for an RTL simulation.

Nevertheless, the processor cores are for themselves not running on their own, but are complex IP blocks that at least need a clock and reset signal and some memories connected to them. You can use one of the popular system-on-chip to try out the processor cores.

OR1200

OR1200 is the original implementation of the OpenRISC 1000 architecture.

The source code can be found on github at openrisc/or1200.

mor1kx

The mor1kx is pretty much a drop in replacement for the original or1200 processor but it has its advantages.

It follows, in our opinion, better coding standards compared to the or1200
It is licensed under the CERN Open Hardware Licence Version 2 which is suited for open hardware
It’s implementation is highly reconfigurable allowing to be resized to meet target size and performance requirements.
It has docs that explain the overall design.

In 2014 the author, Julius Baxter, gave the following presentation about mor1kx which goes into detail about the motivation for the processor rewrite and architecture.

The source code can be found on github at openrisc/mor1kx

To build a system with mor1kx have a look at the some of the hardware tutorials or have a look at some of the systems available in orpsoc-cores which can be built with FuseSoC.

marocchino

The marocchino OpenRISC implementation also has the advanced features of the mor1kx. The marocchino then expands on this with more advanced features:

A 64-bit FPU implementing OpenRISC’s ORFPX64A32 extension.
It implements an Out-of-order pipeline which helps to avoid pipeline stall’s providing higher execution performance.

The source code can be found on github at openrisc/or1k_marocchino

Stafford Horne has written a few blog articles on how to use marocchino and it’s design. Check them out:

Marocchino in Action - how to boot up the marocchino processor.
Marocchino Pipeline - an overview of the marocchino architecture.
Marocchino a Tomasulo Implementation - a deep dive into the marocchino Tomasulo algorithm implementation.

System Simulators

or1ksim

Or1ksim is a generic OpenRISC 1000 architecture simulator capable of emulating OpenRISC based computer systems at the instruction level. It includes models of a range of peripherals, allowing complete systems to be modeled.

qemu

QEMU is a cpu emulator that supports many cpu targets. OpenRISC has been supported since version 1.2.