Jaguar: Live reloading for your ESP32

Jaguar enables live reloading of Toit code when developing for the ESP32, a popular microcontroller.

Develop, update, and restart your code in less than two seconds via WiFi. Use the really fast development cycle to iterate quickly and learn fast!

What is it?

Jaguar is a small Toit application that runs on your ESP32. It uses the capabilities of the Toit virtual machine to let you update and restart your ESP32 code written in Toit over WiFi. Change your code in your editor, update it on your device, and restart it all within seconds. No need to flash over serial, reboot your device, or wait for it to reconnect to your network.

Watch a short video that shows how you can experience Jaguar on your ESP32 in two minutes:

How does it work?

Jaguar runs a small HTTP server that listens for incoming requests. The requests contain compiled Toit programs that are relocated and installed in flash on the device. Before installing a program, we stop any old version of the program and free the resources it has consumed. The new version of the program gets to start again from main.

Community

Use this invite to join our Discord server, and follow the development and get help. We're eager to hear of your experience building with Toit. The Discord chat is publicly accessible through our Linen.

We also use GitHub Discussions to discuss and learn.

We follow a code of conduct in all our community interactions.

How do I use it?

Download

Unless you want to build Jaguar from source, start by downloading and installing the jag binary for your host platform.

On macOS, you can use Homebrew to manage the installation of jag:

brew install toitlang/toit/jag

On Windows 10+ you can use the Windows package manager:

winget install --id=Toit.Jaguar -e

For Archlinux you can install the AUR package jaguar-bin:

yay install jaguar-bin

As alternative to these package managers, we also offer precompiled binaries for download:

• Download Jaguar for macOS (or as an archive)
• Download Jaguar for Windows (or as an archive)
• Download Jaguar for Linux (only as an archive)

If you download an archive, you should unpack it and put the embedded jag or jag.exe binary somewhere on your PATH. The same applies when you extract the jag binary from the macOS jag.dmg file.

Setup associated tools

Next step is to let jag download and configure the Toit SDK and the associated tools for flashing the Jaguar application onto your ESP32:

jag setup

Flashing via serial

Now it is time to connect your ESP32 with a serial cable to your computer and put the Jaguar application onto it. Running jag flash will ask you for the serial port to use and the WiFi credentials, but be aware that the tooling requires permission to access your serial port.

jag flash

If you want to avoid typing the WiFi credentials every time you flash, you can store them in Jaguar's config file with:

jag config wifi set --wifi-ssid SSID --wifi-password PASSWORD

After flashing it is possible to monitor the serial output from the device:

jag monitor

Once the serial output shows that your ESP32 runs the Jaguar application, it will start announcing its presence to the network using UDP broadcast. You can find a device by scanning, but this requires you to be on the same local network as your ESP32:

jag scan

Running code via WiFi

With the scanning complete, you're ready to run your first Toit program on your Jaguar-enabled ESP32 device. Download hello.toit and store it in your file system and then run:

jag run hello.toit

Be aware that you can configure the way your applications run by providing options to jag run. Also, Jaguar is fast enough that it is possible to ask Jaguar to keep watching your Toit code on disk and to live reload it when it changes. Simply write:

jag watch hello.toit

and edit hello.toit or any of the files it depends on in your favorite editor.

Installing services and drivers

Jaguar supports installing named containers that are automatically run when the system boots. They can be used to provide services and implement drivers for peripherals. The services and drivers can be used by applications and as such they form an instrumental part of the extensibility of a Jaguar based system.

You can list the currently installed containers on a device through:

jag container list

This results in a list that shows the container image ids and the associated names.

$ jag container list
85c64060-ffbd-5e04-a0dd-252d5bbf4a32: print-service
4e9a12bc-7f07-5118-9f04-8ad2bbe476d1: jaguar

You install a new, or update an existing, container through:

jag container install print-service service.toit

and you can uninstall said container again using:

jag container uninstall print-service

Updating Jaguar via WiFi

If you upgrade Jaguar, you will need to update the system software and the Jaguar application on your device. You can do this via WiFi simply by invoking:

jag firmware update

Updating the firmware will uninstall all containers and stop running applications, so those have to be transfered to the device again after the update.

Visual Studio Code

The Toit SDK used by Jaguar comes with support for Visual Studio Code. Once installed, you can add the Toit language extension and get full language support for Toit, including syntax highlighting, integrated static analysis, and code completions. Jaguar already comes with everything you need, so if you can run jag from your PATH, the extension will automatically find the Toit SDK downloaded by Jaguar and use that.

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Options for jag run

It is possible to provide options for jag run that control how your applications behave on your device. This section lists the options and provides an explanation for when they might come in handy.

Limiting application run time

You can control how much time Jaguar gives your application to run through the -D jag.timeout setting. It takes a value like 10s, 5m, or 1h to indicate how many seconds, minutes, or hours the app can run before being shut down by Jaguar.

jag run -D jag.timeout=10s service.toit

Defines

Jaguar supports defining values that can be used in your Toit code. This is done through the -D option. Its primary use is to configure Jaguar (see below for temporarily disabling Jaguar), but it can also be used to pass values to your Toit code.

All defined values that are available in the jag.defines assets, where they are stored as Tison. The encoding.tison library has functions to extract these values from the assets.

jag run -D my-define=499 defines.toit

// defines.toit
import encoding.tison
import system.assets

main:
  defines := assets.decode.get "jag.defines"
      --if-present=: tison.decode it
      --if-absent=: {:}
  if defines is not Map:
    throw "defines are malformed"
  print defines["my-define"]

Temporarily disabling Jaguar

You can disable Jaguar while your application runs using the -D jag.disabled. This is useful if Jaguar otherwise interferes with your application. As an example, consider an application that uses the WiFi to setup a software-enabled access point ("Soft AP"). This would normally conflict with Jaguar's use of the WiFi, so your application and Jaguar cannot run at the same time. By temporarily disabling Jaguar, it is possible to test and tinker with the Soft AP based service.

jag run -D jag.disabled softap.toit

By default this runs with a 10 seconds timeout to avoid completely shutting down Jaguar. However, this can be configured by passing a separate -D jag.timeout option:

jag run -D jag.disabled -D jag.timeout=5m softap.toit

This also works for installed containers. Containers that run with -D jag.disabled start when the device boots and runs to completion before Jaguar is enabled. This allows them to control the WiFi and to prevent Jaguar from taking over before they are ready for it:

jag container install -D jag.disabled softap softap.toit

You can also set the timeout for them to make sure they cannot block enabling Jaguar forever:

jag container install -D jag.disabled -D jag.timeout=20s softap softap.toit

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Permission to access serial port

To flash you will need to access the device /dev/ttyUSB0. On Linux that means you probably need to be a member of some group, normally either uucp or dialout. To see which groups you are a member of and which group owns the device, plug in an ESP32 to the USB port and try:

groups
ls -g /dev/ttyUSB0

If you lack a group membership, you can add it with

sudo usermod -aG dialout $USER

You will have to log out and log back in for this to take effect. You can also try newgrp dialout to avoid the need to log out and log back in.

Installing via Go

You can also install using go install. First you'll need to have a Go development environment properly set up (1.16+) and remember to add $HOME/go/bin or %USERPROFILE%\go\bin to your PATH. Using that you can install the jag command line tool through:

go install github.com/toitlang/jaguar/cmd/jag@latest

Building it yourself

You've read this far and you want to know how to build Jaguar and the underlying Toit language implementation yourself? Great! You will need to follow the instructions for building Toit and make sure you can flash a simple example onto your device.

We assume all the commands are executed from this directory (the checkout of the Jaguar repository).

Start by setting the JAG_TOIT_REPO_PATH. Typically, this would be the path to the third_party directory:

export JAG_TOIT_REPO_PATH=$PWD/third_party/toit

Alternatively, JAG_TOIT_REPO_PATH could point to a different checkout of Toit.

Setup the ESP-IDF environment variables and PATHs, which will allow to compile ESP32 programs. The easiest is to just use the export.sh that comes with the ESP-IDF repository:

source $JAG_TOIT_REPO_PATH/third_party/esp-idf/export.sh

Note that Toit's ESP-IDF is patched. Don't use use a plain ESP-IDF checkout instead.

Compile everything.

make

This will build the SDK from the JAG_TOIT_REPO_PATH, then use it to download the Toit dependencies (using toit.pkg) and finally build Jaguar; both the host executable, as well as the Toit program that runs on the device.

You can now use Jaguar as usual:

build/jag flash
sleep 3        # Give the device time to connect to the WiFi.
build/jag scan # Select the new device.
build/jag run $JAG_TOIT_REPO_PATH/examples/hello.toit
build/jag monitor

Contributing

We welcome and value your open source contributions to Jaguar.