In this laboratory you will learn how to build and upload the NuttX OS on your ESP32 Sparrow boards.

Follow this tutorial (alternatively you can build using this and this tutorial) in order to install all tools and build chain.

You can go ahead to section [Run as sudo](#run-as-sudo).

If running on Windows, you must configure a Linux virtual machine through which to access the USB ports of the host. For this you can use the SO virtual machine - a light Ubuntu 20.04 image that comes only with a CLI - or download the latest official image of any other Linux distributions.

If available to you, you can use the VMware Workstation 16 pro which is the easiest to configure - just don't forget to add the USB controller to the VM.

If you do not have access to VMWare, please download VirtualBox. In order to ssh to your virtual machine, please do the following steps:

• add a second network adapter to the VM. The first must be a host-only device in order to provide connectivity from host to guest, while the second will be under NAT and will provide Internet acces.
• boot the virtual machine. Test with ping 8.8.8.8 that you have Internet connectivity
• add a static IP address on the second interface in the 192.168.56.0/56 subnetwork. For mine I used 192.168.56.56/24.

To connect the USB device to the VM instead of the host, head to the upper bar and select Devices > USB Devices > the UART controller .

Currently, the WSL subsystem does not provide native support for USB devices and you must use an open-source tool. Please refer to this for further details.

## Run as sudo

Running as non-root will require a few extra commands for configuration.

Refer to [this](https://blog.espressif.com/getting-started-with-esp32-and-nuttx-fd3e1a3d182c) if you decide to continue as non-root.

Follow the steps below in order to get your Linux machine properly configured:

- install the package dependencies - download the toolchain, since we won't be able to compile with the standard gcc compiler - clone the repositories: nuttx, nuttx-apps - download the prebuilt partition table and bootloader. Alternatively, you can compile your own binaries but this tutorial does not cover it. - compile the NuttX binary - finally, flash the board

## Install dependencies

``` apt-get update apt-get upgrade -y apt-get install -y bison flex gettext texinfo libncurses5-dev libncursesw5-dev gperf automake libtool pkg-config build-essential gperf genromfs libgmp-dev libmpc-dev libmpfr-dev libisl-dev binutils-dev libelf-dev libexpat-dev gcc-multilib g++-multilib picocom u-boot-tools util-linux chrony libusb-dev libusb-1.0.0-dev kconfig-frontends python3-pip ```

## Download the toolchain

``` curl https://dl.espressif.com/dl/xtensa-esp32-elf-gcc8_2_0-esp-2020r2-linux-amd64.tar.gz | tar -xz mkdir /opt/xtensa mv xtensa-esp32-elf/ /opt/xtensa/ echo “export PATH=\$PATH:/opt/xtensa/xtensa-esp32-elf/bin” » ~/.bashrc source ~/.bashrc ```

## Clone the repositories

``` mkdir ~/nuttxspace && cd ~/nuttxspace git clone https://github.com/apache/incubator-nuttx.git nuttx git clone https://github.com/apache/incubator-nuttx-apps.git apps ```

## Download the prebuilt bootloader and partition table

``` mkdir esp-bins curl -L “https://github.com/espressif/esp-nuttx-bootloader/releases/download/latest/bootloader-esp32.bin” -o esp-bins/bootloader-esp32.bin curl -L “https://github.com/espressif/esp-nuttx-bootloader/releases/download/latest/partition-table-esp32.bin” -o esp-bins/partition-table-esp32.bin ```

## Compile and run

Please be aware that, depending on the board version, you might be required to press down the `BOOT` button when flashing the memory - this puts the board in a download state instead of the default boot state. The button must be pressed down only when the connection is being established, as depicted below:

<p align=“center”>

<img src="images/nuttx_download_mode.png" alt="drawing"/>

</p>

``` pip3 install esptool pip3 install pyserial cd ~/nuttxspace/nuttx ./tools/configure.sh esp32-devkitc:nsh make -j4 esptool.py erase_flash make flash ESPTOOL_PORT=/dev/ttyUSB0 ESPTOOL_BAUD=115200 ESPTOOL_BINDIR=../esp-bins picocom /dev/ttyUSB0 -b 115200 ```

Flashing the board could be also done by using `esptool.py –chip esp32 –port /dev/ttyUSB0 –baud 921600 write_flash 0x1000 ../esp-bins/bootloader-esp32.bin 0x8000 ../esp-bins/partition-table-esp32.bin 0x10000 nuttx.bin`.

If the parameters are correct, you should see a log similar to the one below:

<p align=“center”>

<img src="images/nuttx_flash_log.png" alt="drawing" width="650" height="425"/>

</p>

Finally, the boot log should look like this:

<p align=“center”>

<img src="images/nuttx_boot_log.png" alt="drawing" width="600" height="500"/>

</p>