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ardupilot/libraries/AP_Scripting/applets/repl.md

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Lua REPL

This script implements an interactive REPL (read-evaluate-print-loop) for the Lua scripting engine accessible over serial, with line editing, history, and output formatting.

The script can also act as a client for QGroundControl's MAVLink Console functionality (within the Analyze view), subject to limitations detailed below.

Basic Usage

  • Configure a serial port (e.g. SERIALn_PROTOCOL) to protocol 28 (Scripting).
    • By default the first such port is used; this can be adjusted in the script text.
    • SERIAL6 is the alternate USB serial port on Cube Orange, and convenient for bench testing. CAN and network serial ports will also work.
  • Load the repl.lua script onto the autopilot.
  • Connect a terminal emulator to the port and enter Lua statements/expressions at the > prompt, then press Enter to execute. Results and errors will be printed back.
    • A >> prompt indicates that more input is needed to complete the statement.
    • You can use the arrow keys to edit the current and previous inputs.
    • Press ESC twice to clear the input and any incomplete statement then return to an empty prompt.

Autopilot Connection

  • On Linux a convenient command is e.g. minicom -w -D /dev/ttyACM1 -b 115200, assuming you have the minicom terminal emulator installed.
  • Any terminal emulator on any platform should work; see notes below about control codes and other configuration.

SITL Connection

  • Start SITL with a command like Tools/autotest/sim_vehicle.py -A --serialN=tcp:9995:wait to allow connection to the selected serial port.
  • Connect a terminal emulator to localhost TCP port 9995
    • On Linux a convenient command is stty -icanon -echo -icrnl && netcat localhost 9995.
    • Note that you must execute reset to turn echo back on once disconnected.
    • Scripting must be restarted after a TCP reconnection.

MAVLink Connection

  • Requires at least Ardupilot 4.6.
  • Set the port in the script text to nil to enable.
  • In addition to repl.lua, copy the mavport.lua file and MAVLink directory from AP_Scripting/modules to APM/SCRIPTS/MODULES on your autopilot.
  • The ESC key is not supported; cause a syntax error to reset the prompt.
  • The experience over a radio link might be sub-par due to lack of any sort of packet loss tracking or retransmission.

Notes and Limitations

  • Statements like local x = 3 create a variable which immediately goes out of scope once evaluated. Names must be global to survive to the next prompt.
  • There is currently no facility for installing periodic update callbacks.
  • While theoretically impossible to accidentally crash the autopilot software, certain scripting APIs can cause damage to you or your vehicle if used improperly. Use extreme caution with an armed vehicle!
  • The script expects Enter to be \r, \r\n, or \n. It prints \r\n for a new line, and uses ANSI cursor control codes for line editing and history. Check your terminal configuration if Enter doesn't work or you see garbage characters. Lines longer than the terminal width likely won't edit properly.
  • Evaluating complex statements or printing complex results can cause an exceeded time limit error, stopping the script and losing variables and history. Increasing the vehicle's SCR_VM_I_COUNT parameter reduces the chance of this occurring.