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GreenWaves Technologies

Setting up the GAP8 SDK


The GAP8 SDK allows you to compile and execute applications on the GAP8 IoT Application Processor. This SDK is an extract of the necessary elements from the pulp-sdk ( produced by the PULP project, to provide a development environment for the GAP8 series processors.

We provide you with a set of tool and two different operating systems for GAP8:

  • Tools

    • GAP8 RISCV GNU toolchain: a pre-compiled toolchain inherited from RISC V project with support for our extensions to the RISC-V Instruction Set Architecture.
      • Program / control GAP8
      • Debug your application using GDB
      • Program the GAPuino flash memory with applications
    • NNTOOL: a set of tool based on python helps to port NN graphs from various NN training packages to GAP8
    • Autotiler: a code generator for GAP8, which can generate a user algorithm (CNN, MatrixAdd, MatrixMult, FFT, MFCC, etc) with optimized memory management.
    • gapy: a set of tool based on python for building the flashimage, creating partitions, creating FS, executing the openOCD, etc.
  • Operating Systems

    • PULP OS - The open source embedded RTOS produced by the PULP project
    • FreeRTOS - FreeRTOS is an open source real time operating system. GreenWaves Technologies has ported it to GAP8
    • PMSIS - PMSIS is an open-source system layer which any operating system can implement to provide a common API to applications. We currently provide it for PULP OS and FreeRTOS, and it is used by our applications to be portable.

Getting started with the GAP SDK

Ubuntu 18.04

These instructions were developed using a fresh Ubuntu 18.04 Bionic Beaver 64-Bit virtual machine from

The following packages needed to be installed:

sudo apt-get install -y build-essential git libftdi-dev libftdi1 doxygen python3-pip libsdl2-dev curl cmake libusb-1.0-0-dev scons gtkwave libsndfile1-dev rsync autoconf automake texinfo libtool pkg-config libsdl2-ttf-dev

An openocd build for gap8 should be cloned and installed:

git clone
cd gap8_openocd
./configure --program-prefix=gap8- --prefix=/usr --datarootdir=/usr/share/gap8-openocd
make -j
sudo make -j install

#Finally, copy openocd udev rules and reload udev rules
sudo cp /usr/share/gap8-openocd/openocd/contrib/60-openocd.rules /etc/udev/rules.d
sudo udevadm control --reload-rules && sudo udevadm trigger

Now, add your user to dialout group.

sudo usermod -a -G dialout <username>
# This will require a logout / login to take effect

Finally, logout of your session and log back in.

If you are using a Virtual Machine make sure that you give control of the FTDI device to your virtual machine. Plug the GAPuino into your USB port and then allow the virtual machine to access it. For example, for VirtualBox go to Devices->USB and select the device.

Please also make sure that your Virtual Machine USB emulation matches your PC USB version. A mismatch causes the USB interface to be very slow.

The following instructions assume that you install the GAP SDK into your home directory. If you want to put it somewhere else then please modify them accordingly.

Ubuntu 16.04

You can follow the steps for Ubuntu 18.04 except for the following instructions.

After you have installed the system packages with apt-get, you need to also create this symbolic link:

sudo ln -s /usr/bin/libftdi-config /usr/bin/libftdi1-config

Also, you may need to install git lfs

curl -s | sudo bash
sudo apt-get install git-lfs
git lfs install

Download and install the toolchain:

Now clone the GAP8 SDK and the GAP8/RISC-V toolchain:

git clone

In case you use an old git version, you may need to use these commands instead:

git lfs clone

Install the toolchain (this may require to launch the script through sudo):

cd ~/gap_riscv_toolchain_ubuntu_18

Finally, clone the sdk (adapt gap_sdk path according to your needs)

git clone
cd ~/gap_sdk

Configure the SDK:

You can either source in the root sdk folder and then select the right board from the list, or directly source the board config.



# replace by the board you want
source config/

If you directly source the board config, you need to source the appropriate config file for the board that you have. The SDK supports 2 boards (gapuino and gapoc) and each of them can use version 1 or version 2 of the GAP8 chip. Boards bought before 10/2019 contains GAP8 version 1 and use a USB B plug for JTAG while the ones bought after contains version 2 and use a USB micro B for JTAG.

Hereafter you can find a summary of the available boards and their configuration file.

Board Chip Config file
Gapuino GAP8 v1 configs/
Gapuino GAP8 v2 configs/
Gapoc GAP8 v1 configs/
Gapoc GAP8 v2 configs/

Once the proper config file is sourced, you can proceed with the SDK build.

Note that after the SDK has been built, you can source another board config file to change the board configuration, in case you want to use a different board. In this case the SDK will have to be built again. As soon as the SDK has been built once for a board configuration, it does not need to be built again for this configuration, unless the SDK is cleaned.

Minimal install (FreeRTOS only, no neural network tools)

We will first make a minimal install to check whether previous steps were successful. If you are only doing board bringup or peripheral testing, this install will also be a sufficient.

Python requirements

Our modules (gapy runner) require a few additional Python packages that you can install with this command from Gap SDK root folder:

pip3 install -r requirements.txt

SDK install

Initialize and download all sub projects required to run pmsis_examples on a board (freertos, pmsis_api, gapy and bsp):

First, use the following command to configure the shell environment correctly for the GAP SDK. It must be done for each terminal session**:

cd ~/gap_sdk
# Choose which board

Tip: You can add an "alias" command as follows in your .bashrc file:

alias GAP_SDK='cd ~/gap_sdk && source'

Typing GAP_SDK will now change to the gap_sdk directory and execute the source command.

Then, compile the minimal set of dependencies to run examples:

make minimal_sdk


Finally try a test project. First connect your GAPuino to your PCs USB port. Now, you should be able to run your first helloworld on the board.

cd examples/pmsis/helloworld
make clean && make PMSIS_OS=freertos platform=board io=host all -j && make platform=board io=host run

In details: PMSIS_OS allows us to choose an OS (freertos/pulpos), platform allows to choose the runner (board/gvsoc) and io choose the default output for printf (host/uart).

After the build you should see an output resembling:

     *** PMSIS HelloWorld ***

     Entering main controller
     [32 0] Hello World!
     Cluster master core entry
     [0 7] Hello World!
     [0 0] Hello World!
     [0 4] Hello World!
     [0 5] Hello World!
     [0 3] Hello World!
     [0 1] Hello World!
     [0 2] Hello World!
     [0 6] Hello World!
     Cluster master core exit
     Test success !
     Detected end of application, exiting with status: 0
     Loop exited
     commands completed

If this fails, ensure that you followed previous steps correctly (openocd install, udev rules). If libusb fails with a permission error, you might need to reboot to apply all changes.

If you need Gap tools for neural networks (nntool) or the Autotiler, please follow the next section

If you just wish to also have access to pulp-os simply type:

# checkout all needed submodules
make pulpos.all
# compile pulp-os and its librairies
make pulp-os

And replace PMSIS_OS=freertos by PMSIS_OS=pulpos on your run command line.

Full Install

Python requirements

In order to use the Gap tools for neural networks (nntool), we strongly encourage to install the Anaconda distribution ( Python3 ). You can find more information here:

Note that this is needed only if you want to use nntool, you can skip this step otherwise. Once Anaconda is installed, you need to activate it and install python modules for this tool with this command:

pip install -r tools/nntool/requirements.txt
pip install -r requirements.txt

Pull and compile the full tool suite

Finally, we install the full tool suite of the sdk (including nntool and autotiler).

git submodule update --init --recursive
make sdk

Note that if you only need autotiler (and not nntool) you can instead use:

git submodule update --init --recursive
make all && make autotiler


OpenOCD for Gap8 is now used instead of plpbridge. There are a few applications which require OpenOCD, as they are using OpenOCD semi-hosting to transfer files with the workstation.

You have to install the system dependencies required by OpenOCD that you can find here:

There are different cables setup by default for each board. In case you want to use a different cable, you can define this environment variable:

export GAPY_OPENOCD_CABLE=interface/ftdi/olimex-arm-usb-ocd-h.cfg

Using the virtual platform

If you only followed Minimal installation process, begin by compiling gvsoc:

make gvsoc

You can also run this example on the Gap virtual platform with this command:

make clean all run platform=gvsoc PMSIS_OS=freertos/pulpos

You can also generate VCD traces to see more details about the execution:

make clean all run platform=gvsoc runner_args=--vcd

You should see a message from the platform telling how to open the profiler.

Using the flasher (Hyperflash)

As soon as at least one file for a file-system is specified, the command "make all" will also build a flash image containing the file systems and upload it to the flash.

For example, you can include files for the readfs file-system with these flags in your Makefile:

READFS_FILES += <file1> <file2> <file3> ......

In case you don't have any file but you still want to upload the flash image, for example for booting from flash, you can execute after you compiled your application:

make flash

In case you specified files, the command "make all" will not only build the application but also build the flash image and upload it to the flash. In case you just want to build your application, you can do:

make build

Then after that if you want to produce the flash image and upload it, you can do:

make image flash

Boot from flash

The board is by default configured to boot through JTAG. If you want to boot from flash, you need to first program a few efuses to tell the ROM to boot from flash. Be careful that this is a permanent operation, even though it will still be possible to boot from JTAG. This will just always boot from flash when you power-up the board or reset it. To program the efuses, execute the following command and follow the instructions:

# if using hyperflash:
# if using spiflash:

If you choose to boot your application from Flash, and you want to view the output of printf's in your code then you can first compile your application with the printf redirected on the UART with this command:

make clean all platform=board PMSIS_OS=your_os io=uart

You can also use a terminal program, like "cutecom":

sudo apt-get install -y cutecom

Then please configure your terminal program to use /dev/ttyUSB1 with a 115200 baud rate, 8 data bits and 1 stop bit.


Build the documentation:

cd gap_sdk
make docs

If you haven't download and install the autotiler, you will probably have some warnings when you build the docs. All the documentations are available on our website:

You can read the documentation by opening gap_doc.html in the docs folder in your browser:

firefox docs/gap_doc.html

If you would like PDF versions of the reference manuals you can do:

cd docs
make pdf

Upgrading/Downgrading the SDK

If you want to upgrade/downgrade your SDK to a new/old version:

cd gap_sdk
git checkout master && git pull
git checkout <release tag name>
git submodule sync --recursive
# For minimal install
make clean minimal_sdk
# for full install
git submodule update --init --recursive
make clean sdk

Please check our release tags here to ensure the version:

Getting help

Please log any issues you have with the SDK in the github project.

We have also created a GAP8 developers’ forum for you to ask questions and find out more about the GAP8 SDK. You can join this group at

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