Microwatt

A tiny Open POWER ISA softcore written in VHDL 2008. It aims to be simple and easy to understand.

Simulation using ghdl

You can try out Microwatt/Micropython without hardware by using the ghdl simulator. If you want to build directly for a hardware target board, see below.

• Build micropython. If you aren't building on a ppc64le box you will need a cross compiler. If it isn't available on your distro grab the powerpc64le-power8 toolchain from https://toolchains.bootlin.com

git clone https://github.com/micropython/micropython.git
cd micropython
cd ports/powerpc
make -j$(nproc)
cd ../../../

• Microwatt uses ghdl for simulation. Either install this from your distro or build it. Next build microwatt:

git clone https://github.com/antonblanchard/microwatt
cd microwatt
make

• Link in the micropython image:

ln -s ../micropython/ports/powerpc/build/firmware.bin main_ram.bin

• Now run microwatt, sending debug output to /dev/null:

./core_tb > /dev/null

Synthesis on Xilinx FPGAs using Vivado

• Install Vivado (I'm using the free 2019.1 webpack edition).

• Setup Vivado paths:

source /opt/Xilinx/Vivado/2019.1/settings64.sh

• Install FuseSoC:

pip3 install --user -U fusesoc

Fedora users can get FuseSoC package via

sudo dnf copr enable sharkcz/danny
sudo dnf install fusesoc

• Create a working directory and point FuseSoC at microwatt:

mkdir microwatt-fusesoc
cd microwatt-fusesoc
fusesoc library add microwatt /path/to/microwatt/

• Build using FuseSoC. For hello world (Replace nexys_video with your FPGA board such as --target=arty_a7-100):

fusesoc run --target=nexys_video microwatt --memory_size=8192 --ram_init_file=/path/to/microwatt/fpga/hello_world.hex

You should then be able to see output via the serial port of the board (/dev/ttyUSB1, 115200 for example assuming standard clock speeds). There is a know bug where initial output may not be sent - try the reset (not programming button on your board if you don't see anything.

• To build micropython (currently requires 1MB of BRAM eg an Artix-7 A200):

fusesoc run --target=nexys_video microwatt

Testing

• A simple test suite containing random execution test cases and a couple of micropython test cases can be run with:

make -j$(nproc) check

Issues

This is functional, but very simple. We still have quite a lot to do:

• There are a few instructions still to be implemented
• Need to add caches and bypassing (in progress)
• Need to add supervisor state (in progress)