# The Potato Processor

![Processor architecture overview diagramme](https://github.com/skordal/potato/blob/master/docs/diagram.png?raw=true)

The Potato Processor is a simple RISC-V processor written in VHDL for use in FPGAs. It implements the 32-bit integer subset
of the RISC-V Specification version 2.0 and supports large parts of the the machine mode specified in the RISC-V Privileged
Architecture Specification v1.10.

The processor has been tested on an Arty board using the example SoC design provided in the `example/` directory
and the applications found in the `software/` directory. Synthesis and implementation has been tested on various versions
of Xilinx' Vivado toolchain, most recently version 2019.2.

## Features

* Supports the complete 32-bit RISC-V base integer ISA (RV32I) version 2.0
* Supports large parts of the machine mode defined in the RISC-V Privileged Architecture version 1.10
* Supports up to 8 individually maskable external interrupts (IRQs)
* 5-stage "classic" RISC pipeline
* Optional instruction cache
* Supports the Wishbone bus, version B4

## Peripherals

The project includes a variety of Wishbone-compatible peripherals for use in system-on-chip designs based on the Potato processor.
The main peripherals are:

* Timer - a 32-bit timer with compare interrupt
* GPIO - a configurable-width generic GPIO module
* Memory - a block RAM memory module
* UART - a UART module with hardware FIFOs, configurable baudrate and RX/TX interrupts

## Quick Start/Instantiating

To instantiate the processor, add the source files from the `src/` folder to your project. Use the `pp_potato`
entity to instantiate a processor with a Wishbone interface. Some generics are provided to configure the processor core.

An example System-on-Chip for the Arty development board can be found in the `example/` directory of the source repository.

## Compiler Toolchain

To program the processor, you need an appropriate compiler toolchain. To compile a working toolchain, go to the
[RISCV GNU toolchain repository](https://github.com/riscv/riscv-gnu-toolchain) and clone the project. Compile and install
the toolchain using the following commands (note that `make` will both build and install the toolchain, ensure that the
destination directory is writeable by your user):

    ./configure --prefix=/opt/riscv-toolchain --with-abi=ilp32 --with-arch=rv32i
    make

## Reporting bugs and issues

Bugs and issues related to the Potato processor can be reported on the project's [GitHub page](https://github.com/skordal/potato).