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PULPino: open-source microcontroller based on a 32-bit RISC-V core

PULPino: open-source microcontroller based on a 32-bit RISC-V core

Introduction

PULPino is an open-source microcontroller system, based on a small 32-bit RISC-V core developed at ETH Zurich. The core has an IPC close to 1, full support for the base integer instruction set (RV32I), compressed instructions (RV32C) and partial support for the multiplication instruction set extension (RV32M). It implements several ISA extensions such as: hardware loops, post-incrementing load and store instructions, ALU and MAC operations, which increase the efficiency of the core in low-power signal processing applications.

To allow embedded operating systems such as FreeRTOS to run, a subset of the privileged specification is supported. When the core is idle, the platform can be put into a low power mode, where only a simple event unit is active and everything else is clock-gated and consumes minimal power (leakage). A specialized event unit wakes up the core in case an event/interrupt arrives.

For communication with the outside world, PULPino contains a broad set of peripherals, including I2S, I2C, SPI and UART. The platform internal devices can be accessed from outside via JTAG and SPI which allows pre-loading RAMs with executable code. In standalone mode, the platform boots from an internal boot ROM and loads its program from an external SPI flash.

The PULPino platform is available for RTL simulation as well FPGA. PULPino has been taped-out as an ASIC in UMC 65nm in January 2016. It has full debug support on all targets. In addition we support extended profiling with source code annotated execution times through KCacheGrind in RTL simulations.

Requirements

PULPino has the following requirements

  • ModelSim in reasonably recent version (we tested it with versions >= 10.2c)
  • CMake >= 2.8.0, versions greater than 3.1.0 recommended due to support for ninja
  • riscv-toolchain, specifically you need riscv32-unknown-elf-gcc compiler and friends. There are two choices for this toolchain: Either using the official RISC-V toolchain supported by Berkeley or the custom RISC-V toolchain from ETH. The ETH version supports all the ISA extensions that were incorporated into the RI5CY core.
  • python2 >= 2.6

Editions

There are two PULPino editions available, one for OR1K based on the OR10N core and one for RISCV based on the RI5CY core. Only the RISC-V based version is currently open-source. The software included in this repository is compatible with both ISAs and automatically targets the correct ISA based on the compiler used.

The simulator (modelsim) must be explicitely told which edition you want to build. Use the environment variable PULP_CORE and set it to either OR10N or riscv. It defaults to riscv when not set.

Version Control

PULPino uses multiple git subrepositories

To clone those subrepositores and update them, use

./update-ips.py 

This script will read the ips_lists.txt file and update to the versions specified in there. You can choose specific commits, tags or branches.

Documentation

There is a preliminary datasheet available that includes a block diagram and a memory map of PULPino. See docs/datasheet/ in this repository.

It is written in LaTeX and there is no pdf included in the repository. Simply type

make all 

inside the folder to generate the pdf. Note that you need a working version of latex for this step.

Running simulations

The software is built using CMake. Create a build folder somewhere, e.g. in the sw folder

mkdir build 

Copy the cmake-configure.{or1k/riscv}.{gcc/llvm}.sh bash script to the build folder. This script can be found in the sw subfolder of the git repository.

Modify the cmake-configure script to your needs and execute it inside the build folder. This will setup everything to perform simulations using ModelSim.

Inside the build folder, execute

make vcompile 

to compile the RTL libraries using ModelSim. CMake automatically takes care of setting the PULP_CORE environment variable to the correct value based on the compiler you specified when configuring cmake.

To run a simulation in the modelsim GUI use

make helloworld.vsim 

To run simulations in the modelsim console use

make helloworld.vsimc 

This will output a summary at the end of the simulation. This is intended for batch processing of a large number of tests.

Replace helloworld with the test/application you want to run.

Using ninja instead of make

You can use ninja instead make to build software for PULPino, just replace all occurences of make with ninja. The same targets are supported on both make and ninja.

Interactive debug

To interactively debug software via gdb, you need the jtag bridge as well as a working version of gdb for the ISA you want to debug. The debug bridge depends on the jtag_dpi package that emulates a JTAG port and provides a TCP socket to which the jtag bridge can connect to.

Utilities

We additionally provide some utilitiy targets that are supposed to make development for PULPino easier.

For disassembling a program call

make helloworld.read 

To regenerate the bootcode and copy it to the rtl folder use

make boot_code.install 

FPGA

PULPino can be synthesized and run on a ZedBoard. Take a look at the fpga subfolder for more information.

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