# Microwatt

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

## Simulation using ghdl
<p align="center">
<img src="http://neuling.org/microwatt-micropython.gif" alt="MicroPython running on Microwatt"/>
</p>

- 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/mikey/micropython
cd micropython
git checkout powerpc
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 simple_ram_behavioural.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
```

- 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):

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

- 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:

- Need to implement a simple non pipelined divide
- There are a few instructions still to be implemented
- Need to add caches and bypassing (in progress)
- Need to add supervisor state (in progress)