ESPTerm

ESPTerm is a VT100-like terminal emulator running on the ESP8266 WiFi chip.

Fig 1: Breadboard adapter developed for ESPTerm

As of release 1.0, ESPTerm passes most of VTTEST test cases (from the main menu and some Xterm specific), making it functionally comparable to eg. gnome-terminal, terminator, konsole, GtkTerm or PuTTY. ESPTerm is capable of running Midnight Commander through agetty, including full mouse support, provided agetty is made to believe it's Xterm, which shows ESPTerm is sufficiently well implemented to work with ncurses.

To see what escape sequences are supported, check out this annotated Xterm manual page which was used for reference, or the built-in help page (online demo)

The terminal screen can be accessed using any web browser, even on a phone or tablet. It works with ESP-01, ESP-01S, ESP-12 and likely many other modules (I use an ESP-12 on a LoLin NodeMCU board from eBay for development).

With ESPTerm, you can add remote access via WiFi to any embeded project, all you need is a serial port and some imagination!

Try it online

You can try the web user interface here: espterm.github.io

The demo is almost identical to the real thing, except, of course, it doesn't do much without the emulator backend that runs on the ESP8266. The web version will be updated to match this repository after each minor release (and sometimes in between for testing; the version currently being show-cased can be read on the About page of the demo).

Main features

• Almost complete VT102 emulation with some extras from Xterm, eg.
  • Screen size up to 80x25 (the limit can be modified when compiling from source)
  • All standard text styles and 16 colors supported
  • Full UTF-8 support, alternate character sets
  • Standard mouse tracking modes
  • You can dynamically set screen title, button labels...
• Web Terminal Interface
  • Real-time screen update via WebSocket
  • Mouse and keyboard input, works also on mobile
  • 5 optional buttons for quick commands
  • Text file upload tool with adjustable delays and line endings
  • Built-in help page (demo) with basic troubleshooting and command reference
• User-friendly comprehensive WiFi configuration (Demo: WiFi, network config)
  • Static IP, DHCP, channel selection, power
  • SSID search utility for finding your existing network

Running ESPTerm

To run ESPTerm on your ESP8266, either build it yourself from source using xtensa-lx106-elf-gcc (and the included Makefile), or download pre-built binaries from the GitHub releases section. Flash the binaries using esptool.

Pins

• Pin GPIO2 is used for debug messages at 115200 baud, 8 bit, no parity.
• Pins Rx and Tx are used for the main communication UART, parameters of which can be set on the system config page. Connect your USB-serial dongle or application microcontroller here.

Setup

• When flashed for the first time, ESPTerm wipes any possible previous WiFi configuration, because it implements its own WiFi config manager with many additional features.
• It should start in AP mode, the default SSID being TERM-MACADR with MACADR being three unique bytes from the MAC address / Device ID as ASCII hex.
• Connect to the AP via a smartphone or laptop and configure WiFi as desired. If a captive portal page does not open, try 192.168.4.1 in your web browser.

Rescue from messed up config

It can happen that some changes to the WiFi or network config make the module inaccessible.

• To re-enable the built-in AP, hold the BOOT (GPIO0 -> GND) button for about 1 s, until the blue LED starts flashing. Then quickly release the button.
• To reset all settings to defaults, hold the button a couple seconds until the LED flashes rapidly, then release it.
• You can cancel this wipe/reset operation (when triggered by accident) by pressing Reset or disconnecting the power supply.

Config files

ESPTerm has two config "files", one for defaults and one for the currently used settings. In the case of the terminal config, there is also a third, temporary file for changes done via ESC commands.

When you get your settings just right, you can store them as defaults, which can then be at any time restored by holding the BOOT (GPIO0) button. You can do this on the System Settings page. This asks for an "admin password", which you can define when building the firmware in the esphttpdconfig.mk file.

The default password is 19738426. This password can't presently be changed without re-flashing the firmware.

You can also restore everything (except the saved defaults) to "factory defaults", there is a button for this on the System Settings page. Those are the initial values in the config files.

Research resources

Developing ESPTerm wasn't an easy task, because the information is scattered across many places and the existing terminal emulators I originally used for reference (terminator, Konsole) are not implemented correctly in some details.

A great tool for checking my implementation has proven to be VTTTEST and Xterm as a reference implementation that is probably the most complete emulator available, although it's cumbersome to use and its age really shows in the looks.

I've comnpiled a list of those I found most helpful here: VT100 emulation resources

Development

ESPTerm's firmware is written in C and is based on SpriteTM's libesphttpd http server library forked to MightyPork/libesphttpd. This fork includes various improvements and changes required by the project.

Installation for development

• Clone this project with --recursive, or afterwards run git submodule init and git submodule update.
• Install esp-open-sdk and build it with make toolchain esptool libhal STANDALONE=n. Make sure the xtensa-lx106-elf/bin folder is on $PATH.
• Install esptool (it's in the Arch community repo and on AUR, too)
• Set up udev rules so you have access to ttyUSB0 without root, eg:

  KERNEL=="tty[A-Z]*[0-9]*", GROUP="uucp", MODE="0666"
  

• Install Ragel if you wish to make modifications to the ANSI sequence parser. If not, comment out its call in build_parser.sh. The .rl file is the actual source, the .c is generated.
• Install dependencies of the front-end submodule (yarn install in the front-end folder, installed PHP)
• Make sure your esphttpdconfig.mk is set up properly - link to the SDK etc.

The IoT SDK is now included in the project due to problems with obtaining the correct version and patching it. It works with version 1.5.2, any newer seems to be incompatible. If you get it working with a newer SDK, a PR is more than welcome!

Web resources

The web resources are in the front-end git submodule. To prepare the web resources for a build, run make web. The resulting files are copied to html/. The html/ folder is then embedded in the firmware image.

It's kind of tricky to develop the web resources locally; you might want to try the "split image" Makefile option, then you can flash just the html portion with make htmlflash. I haven't tried this.

For local development, use the server.sh script in html_orig (more details in the front-end repo's readme). It's possible to talk to the API endpoints of a running ESP8266 from a page served by your local server if you configure _env.php with its IP.

Flashing

The Makefile should automatically build the parser and web resources for you when you run make. The web resources are normally no re-built, because the build process is quite slow. To manually rebuild them, run make web before make.

To flash, just run make flash. It will use parameters you setup in the esphttpdconfig.mk file.