Join the chat on Discord

The latest version of this guide will always be available here. At the top of the left sidebar there is a version option if you are running an older version of EdgeTX and need the docs for that specific version.

Please feel free to make suggestions or corrections to the documentation on GitHub, but the preferred method of editing is to use GitBook, so all changes will need to be made by someone who is authorized as a writer there.

This guide covers the development of user-written scripts for R/C transmitters running the EdgeTX 2.9 operating system with Lua support. Readers should be familiar with EdgeTX, the EdgeTX Companion, and know how to transfer files the SD card in the transmitter.

If you are new to Lua programming, you may also find the Lua Reference Manual of assistance.

Part I is an overview of the different script types, along with basic examples of each.

Part II is a programming guide that introduces the types of EdgeTX Lua scripts and how to use them.

Part III is the EdgeTX Lua API Reference

Part IV covers advanced topics with examples

• FUNC_OVERRIDE_CHANNEL

• FUNC_TRAINER

• FUNC_INSTANT_TRIM

• FUNC_RESET

• FUNC_SET_TIMER

• FUNC_ADJUST_GVAR

• FUNC_VOLUME

• FUNC_SET_FAILSAFE

• FUNC_RANGECHECK

• FUNC_BIND

• FUNC_PLAY_SOUND

• FUNC_PLAY_TRACK

• FUNC_PLAY_VALUE

• FUNC_PLAY_SCRIPT

• FUNC_RESERVE5

• FUNC_BACKGND_MUSIC

• FUNC_BACKGND_MUSIC_PAUSE

• FUNC_VARIO

• FUNC_HAPTIC

• FUNC_LOGS

• FUNC_BACKLIGHT

• FUNC_SCREENSHOT

• FUNC_RACING_MODE

• FUNC_DISABLE_TOUCH

Change the working directory

@status current Introduced in 2.3.0

Parameters

• directory (string) New working directory

Return value

none

Flushes audio queue

@status experimental, Introduced in 2.8.0

Parameters

none

Return value

none

Return current RTC system date as unix timstamp (in seconds since 1. Jan 1970)

Please note the RTC timestamp is kept internally as a 32bit integer, which will overflow in 2038.

Parameters

none

Return value

• number Number of seconds elapsed since 1. Jan 1970

Get channel assigned to stick. See Default Channel Order in General Settings

@status current Introduced in 2.0.0

Parameters

• stick (number) stick number (from 0 to 3)

Return value

• number channel assigned to this stick (from 0 to 3)

• nil stick not found

Return rotary encoder mode

@status current Introduced in 2.8.0

Parameters

none

Return value

• number in list: Normal = 0, Both V and H inverted = 1, V-N = 2, V-A = 3

• return 0 on radio without rotary encoder

This section describes the Lua libraries, functions and constants that are provided by EdgeTX.

Reads the value of a logical switch.

@status current Introduced in 2.6

Parameter

• id: integer identifying the logical switch (zero for L01 etc.).

Return value

• value: true/false.

@status current Introduced in 2.6

Parameter

• switchIndex: integer identifying a switch as returned by getSwitchIndex(positionName) or fields in the table returned by model.getLogicalSwitch(switch) identifying switches.

Return value

• value: string naming the switch position as it is shown on radio menus where a switch can be chosen.

Parameters

• sourceIndex: integer identifying a value source as returned by getSourceIndex(sourceName) or the id field in the table returned by getFieldInfo.

Return value

• sourceName: string naming the value source as it is shown on radio menus where a source can be chosen.

Notice

The source names shown on the screen are not the same as the names used by getFieldInfo and getValue. But the indices are the same, so e.g. getValue(index) will work with the indices used here.

Status

Current Introduced in 2.6

Play a time value (text to speech)

@status current Introduced in 2.1.0

Parameters

• duration (number) number of seconds to play. Only integral part is used.

• hourFormat (number):

  • 0 or not present play format: minutes and seconds.

  • != 0

Return value

none

Pops a received Crossfire Telemetry packet from the queue.

@status current Introduced in 2.2.0

Parameters

none

Return value

• nil queue does not contain any (or enough) bytes to form a whole packet

• multiple returns 2 values:

An argument with drawing flags can be given to the various functions that draw on the LCD screen. The lower half of the flags (bits 1-16) are the flag attributes shown below, and the upper half of the flags (bits 17-32) are a color value.

Not all of the flags below should be directly manipulated from Lua, but those that are meant to be set directly by Lua, are accessible by the .

Since the flags are bits, you can add them up to combine, as long as you only add each flag one time. If you add the same flag twice, then it will add up to the next bit over, e.g. INVERS + INVERS = VCENTER. If you want to add a flag to a value where it may already be set, then use flags = bit32.bor(flags, INVERS).

This functions allows for sending SPORT / ACCESS telemetry data toward the receiver, and more generally, to anything connected SPORT bus on the receiver or transmitter.

When called without parameters, it will only return the status of the output buffer without sending anything.

@status current Introduced in 2.3

Parameters

Returns (some of) the general radio settings

@status current Introduced in 2.0.6, imperial added in TODO, language and voice added in 2.2.0, gtimer added in 2.2.2.

Parameters

Get available memory remaining in the Heap for Lua.

Parameters

none

Returns gray value which can be used in LCD functions

@status current Introduced in 2.0.13

Parameters

none

• CHAR_RIGHT

• CHAR_LEFT

• CHAR_UP

Returns radio timers

@status current Introduced added in 2.3.0.

Parameters

none

• LS_FUNC_NONE

• LS_FUNC_VEQUAL

• LS_FUNC_VALMOSTEQUAL

This functions allows for sending telemetry data toward the Ghost link.

When called without parameters, it will only return the status of the output buffer without sending anything.

@status current Introduced in 2.7.0

Parameters

• command command

Return OpenTX version

@status current Introduced in 2.0.0, expanded in 2.1.7, radio type strings changed in 2.2.0, os name added in EdgeTX 2.4.0

Example

This example also runs in OpenTX versions where the function returned only one value:

Output of the above script in simulator:

Return flight mode data.

@status current Introduced in 2.1.7

Parameters

Get RSSI value as well as low and critical RSSI alarm levels (in dB)

@status current Introduced in 2.2.0

Parameters

none

Return the RAS value or nil if no valid hardware found

@status current Introduced in 2.2.0

Parameters

none

Raises a pop-up on screen that shows a warning

@status current Introduced in 2.2.0

Parameters

This function reads/writes the Multi protocol buffer to interact with a protocol².

@status current Introduced in 2.3.2

Parameters

Sets the value of a sticky logical switch.

@status current Introduced in 2.6

Parameters

Play a file from the SD card

@status current Introduced in 2.0.0, changed in 2.1.0

Parameters

Get percent of already used Lua instructions in current script execution cycle.

@status current Introduced in 2.2.1

Parameters

none

Set baudrate for serial port(s) affected to LUA

@status current Introduced in 2.3.12

Parameters

baudrate Desired baudrate

The EdgeTX team has no intention of making a profit from their work - EdgeTX is free and open source and will remain free and open source. However, the project is more expensive to maintain than most open source projects. This in mainly because there is a never ending flood of hardware to integrate and maintain code for. Hardware that costs. In addition, in order to develop for this hardware, certain specalised test and measurement equipment is also required.

In order to support this, EdgeTX has chosen to use OpenCollective to allow for donations from the community, as well as funding from manufacturers who choose to partner with and sponsor the project. This also allows for transparent accounting of what the funds are spent on.

Please visit if you would like to financially help support the project!

@status current Introduced in 2.6

Parameter

• switchIndex: integer identifying a switch as returned by getSwitchIndex(positionName)

@status current Introduced in 2.9.0

Parameters

• port_nr: valid values are only 0 and 1 on radios that have SWSERIALPOWER defined

Return the time since the radio was started in multiple of 10ms

The timer internally uses a 32-bit counter which is enough for 497 days so overflows will not happen.

@status current Introduced in 2.0.0

Parameters

none

This is an iterator function over switch positions.

for switchIndex, switchName in switches() do ...

will iterate over all available switch positions.

Parameters

Resets the radio global timer to 0.

@status current Introduced in 2.2.2, param added in 2.3

Parameters

Set all inputs to defaults

@status current Introduced in 2.0.0

Parameters

none

Return current system date and time that is kept by the RTC unit

Parameters

none

Pops a received SPORT packet from the queue. Please note that only packets using a data ID within 0x5000 to 0x50FF (frame ID == 0x10), as well as packets with a frame ID equal 0x32 (regardless of the data ID) will be passed to the LUA telemetry receive queue.

@status current Introduced in 2.2.0

Parameters

none

Clear all flightModes

@status current Introduced in 2.3.10

Parameters

none

This is an iterator function over value sources.

for sourceIndex, sourceName in sources() do ...

will iterate over all available value sources.

Parameters

Raises a pop-up on screen that asks for confirmation

@status current Introduced in 2.2.0, changed from (title, event) to (title, message, event) in 2.3.8

Parameters

• title (string) title to display

• message (string) text to display

• event (number) the event variable that is passed in from the Run function (key pressed)

Return value

• "CANCEL" user pushed EXIT key

Notice

Use only from stand-alone and telemetry scripts.

@status current Introduced in 2.8.0

Parameters

• outputIndex: integer identifying the output channel number 0 for CH1, up to MAX_OUTPUT_CHANNELS - 1.

Return value

• value current output value (number). Zero is returned for:

• non-existing outputs

@status current Introduced in 2.9.0

Parameters

• port_nr: valid values are only 0 and 1 on radios that have SWSERIALPOWER defined

  • 0 - first serial port, e.g. on TX16S AUX1

  • 1 - second serial port, e.g. on TX16S AUX2

Return value

• value: true for power enabled, false for power disabled.

• nil serial port power control not available

Parameters

• sourceName: string naming a value source as it is shown on radio menus where you can select it. Notice that many names have special characters in them.

Return value

• sourceIndex: integer. The source index, which can be used as input for getSourceName(sourceIndex), getValue(sourceIndex), and getFieldInfo(sourceIndex).

Notice

The source names shown on the screen are not the same as the names used by getFieldInfo and getValue. But the indices are the same, so e.g. getValue(index) will work with the indices obtained here.

This function is rather time consuming, and should not be used repeatedly in a script, if it can be avoided.

Status

Current Introduced in 2.6

Get stick that is assigned to a channel. See Default Channel Order in General Settings.

@status current Introduced in 2.0.0

Parameters

• channel (number) channel number (0 means CH1)

Return value

• number Stick assigned to this channel (from 0 to 3)

Raises a pop-up on screen that allows uses input

@status current Introduced in 2.0.0

Parameters

• title (string) text to display

• event (number) the event variable that is passed in from the Run function (key pressed)

• input (number) value that can be adjusted by the +/­- keys

• min (number) min value that input can reach (by pressing the -­ key)

• max (number) max value that input can reach

Return value

• number result of the input adjustment

• "OK" user pushed ENT key

• "CANCEL" user pushed EXIT key

Notice

Use only from stand-alone and telemetry scripts.

This functions allows for sending telemetry data toward the TBS Crossfire link.

When called without parameters, it will only return the status of the output buffer without sending anything.

@status current Introduced in 2.2.0, retval nil added in 2.3.4

Parameters

• command command

• data table of data bytes

Return value

• boolean data queued in output buffer or not.

• nil incorrect telemetry protocol.

Return rotary encoder current speed

@status current Introduced in 2.3.10

Parameters

none

Return value

• number in list: ROTENC_LOWSPEED, ROTENC_MIDSPEED, ROTENC_HIGHSPEED

• return 0 on radio without rotary encoder

@param str (string) String to be written to the serial port.

Writes a string to the serial port. The string is allowed to contain any character, including 0.

@status current Introduced in 2.3.10

Parameters

none

Return value

none

Delete all Inputs

@status current Introduced in 2.0.0

Parameters

none

Return value

none

@param num (optional): maximum number of bytes to read. If non-zero, serialRead will read up to num characters from the buffer. If 0 or left out, serialRead will read up to and including the first newline character or the end of the buffer. Note that the returned string may not end in a newline if this character is not present in the buffer.

Reads characters from the serial port. The string is allowed to contain any character, including 0.

@status current Introduced in 2.3.8

Parameters

none

Return value

• str string. Empty if no new characters were available.

The io.close() function is used to close open file.

Parameters

• file object a file object that was returned by the io.open() function.

Return value

• none

Delete line from specified input

@status current Introduced in 2.0.0

Parameters

• input (unsigned number) input number (use 0 for Input1)

• line (unsigned number) input line (use 0 for first line)

Return value

none

Downloading EdgeTX Companion

EdgeTX Companion 2.9 is available for download here (pick the appropriate download for your operating system from Assets heading at the bottom of the page - the filename will have cpn in the name).

Enabling support for Mixer Scripts

If you intend to use mixer scripts, when compiling the firmware for your transmitter you need to make sure the LUA_MIXER option is set. This is not required if you only intend to run any of the other types of Lua script (i.e. telemetry, one-time, function scripts, widgets) as support for those is included by default.

This section provides more specifics on the EdgeTX Lua implementation. Here you will find syntax rules for interface tables and functions.

The loadScript(<file>) function will load a script from a the file and return a function that is the body of the script, as described in the previous section. So you could have the following Lua script file saved on the SD card:

-- /SCRIPTS/TestScript.lua
local c = ...

local function f(x)
  return x + c
end

return f

You can load and use the above file with the following code:

local chunk = loadScript("/SCRIPTS/TestScript.lua")

local f1 = chunk(1)
local y = f1(5)
-- y = 5 + 1

local f2 = chunk(3)
local z = f2(5)
-- z = 5 + 3

So here we put together what we learned in the previous section. The body of the script is an anonymous function returned by loadScript and stored in the variable chunk. It returns the function f when it is called. The local variable c in the script is assigned to the first vararg passed to the call. Since a new closure is created every time we call chunk, f1 and f2 have different closures with different values of c.

Play a tone

@status current Introduced in 2.1.0

Parameters

• frequency (number) tone frequency in Hz (from 150 to 15000)

• duration (number) length of the tone in milliseconds

• pause (number) length of the silence after the tone in milliseconds

• flags (number):

  • 0 or not present play with normal priority.

  • PLAY_BACKGROUND

• freqIncr (number) positive number increases the tone pitch (frequency with time), negative number decreases it. The frequency changes every 10 milliseconds, the change is freqIncr * 10Hz. The valid range is from -127 to 127.

Return value

none

There are several option types that can be specified in the widget options table, which are exposed to the user via the Widget Settings menu. For example:

-- Create a table with default options
-- Options can be changed by the user from the Widget Settings menu
-- Notice that each line is a table inside { }
local options = {
  { "Source", SOURCE, 1 },
  -- BOOL is actually not a boolean, but toggles between 0 and 1
  { "Boolean", BOOL, 1 },
  { "Value", VALUE, 1, 0, 10},
  { "Color", COLOR, ORANGE },
  { "Text", STRING, "Max8chrs" }
}

@status current Introduced in 2.2.0

Parameters

• id Id of the sensor, valid range is from 0 to 0xFFFF

• subID subID of the sensor, usually 0, valid range is from 0 to 7

• instance instance of the sensor (SensorID), valid range is from 0 to 0xFF

• value fed to the sensor

• unit unit of the sensor

• precision the precision of the sensor

  • 0 or not present no decimal precision.

  • != 0

• name (string) Name of the sensor if it does not yet exist (4 chars).

  • not present Name defaults to the Id.

  • present

Return value

• true, if the sensor was just added. In this case the value is ignored (subsequent call will set the value)

Notice

All three parameters id, subID and instance can't be zero at the same time. At least one of them must be different from zero.

@status current Introduced in 2.6

Parameters

• positionName: string naming a switch position as it is shown on radio menus where you can select a switch. Notice that many names have special characters in them like arrow up/down etc. (see ).

Return value

• value: integer. The switchIndex, which can be used as input for `getSwitchName(switchIndex)` and `getSwitchValue(switchIndex)`. Also corresponds to the fields in the table returned by `model.getLogicalSwitch(switch)` identifying switches.

Generate haptic feedback

@status current Introduced in 2.2.0

Parameters

• duration (number) length of the haptic feedback in milliseconds

• pause (number) length of the silence after haptic feedback in milliseconds

• flags (number):

  • 0 or not present play with normal priority

  • PLAY_NOW

Return value

none

Return the internal GPS position or nil if no valid hardware found

@status current Introduced in 2.2.2

Parameters

none

Return value

• table representing the current radio position

  • lat (number) internal GPS latitude, positive is North

Sets the value of a shared memory variable that can be used for passing data between Lua widgets and other Lua scripts.

@status current Introduced in 2.6

Parameters

• id: integer between 1 and 16 identifying the shared memory variable.

Pops a received Ghost Telemetry packet from the queue.

@status current Introduced in 2.7.0

Parameters

none

Return value

Stops key state machine. See for the detailed description.

@status current Introduced in 2.0.0

Parameters

The io.open() function is used to open the file on SD card for subsequent reading or writing. After the script is done with the file manipulation io.close() function should be used.

Parameters

• filename

The following touch events are passed in the event argument to the widget script refresh function (when in full screen mode), just like the key events. The following touch events are provided:

In addition to the above touch events a touchState table is passed to refresh with the following addional data fields:

Notes:

• touchState is nil if event is not a touch event. This can be used to test if we have a touch event or a key event.

  • Since Lua evaluates a nil value to false and everything else to true

Return detailed information about field (source)

The list of valid sources is available:

@status current Introduced in 2.0.8, 'unit' field added in 2.2.0

Parameters

• source can be an identifier (number) or a name (string) of the source.

Return value

• table information about requested field, table elements:

  • id (number) field identifier

Load a Lua script file. This is similar to Lua's own loadfile() API method, but it uses OpenTx's optional pre-compilation feature to save memory and time during load.

Return values are same as from Lua API loadfile() method: If the script was loaded w/out errors then the loaded script (or "chunk") is returned as a function. Otherwise, returns nil plus the error message.

@status current Introduced in 2.2.0

Example

Parameters

• file (string) Full path and file name of script. The file extension is optional and ignored (see mode param to control which extension will be used). However, if an extension is specified, it should be ".lua" (or ".luac"), otherwise it is treated as part of the file name and the .lua/.luac will be appended to that.

• mode (string) (optional) Controls whether to force loading the text (.lua) or pre-compiled binary (.luac) version of the script. By default OTx will load the newest version and compile a new binary if necessary (overwriting any existing .luac version of the same script, and stripping some debug info like line numbers). You can use mode to control the loading behavior more specifically. Possible values are:

Return value

• function The loaded script, or nil if there was an error (e.g. file not found or syntax error).

• string Error message(s), if any. Blank if no error occurred.

Notice

Note that you will get an error if you specify mode as "b" or "t" and that specific version of the file does not exist (eg. no .luac file when "b" is used). Also note that mode is NOT passed on to Lua's loader function, so unlike with loadfile() the actual file content is not checked (as if no mode or "bt" were passed to loadfile()).

In general terms, there are two different types of data that can be exchanged with EdgeTX:

• Values, which generally fall on a scale between -1024 and 1024, also sometimes reported as -100% to 100%, e.g. for mixer values and channel outputs.

• Switches, which are either true or false.

The io library has been simplified and only a subset of functions and their functionality is available. What follows is a complete reference of io functions that are available to EdgeTX scripts

Available functions:

• io.open()

Overview

Function scripts are invoked via the 'Lua Script' option of Special Functions configuration page.

Typical uses of Function scripts are:

Overview

Telemetry scripts are used for building customized screens. Each model can have up to three active scripts as configured on the model's telemetry configuration page. The same script can be assigned to multiple models.

Please note: Telemetry scripts are only available on radios with telemetry screens, such as e.g. FrSky Taranis models (including Xlite), Radiomaster TX12 and and Jumper T12.

The io.write() function is used to write data to the file on SD card.

Parameters

• file object a file object that was returned by the io.open() function. The file must be opened in write or append mode.

Gets the value of a shared memory variable that can be used for passing data between Lua widgets and other Lua scripts.

@status current Introduced in 2.6

Parameters

• id: integer between 1 and 16 identifying the shared memory variable.

Return value

This functions allows for sending SPORT telemetry data toward the receiver, and more generally, to anything connected SPORT bus on the receiver or transmitter.

When called without parameters, it will only return the status of the output buffer without sending anything.

@status current Introduced in 2.2.0, retval nil added in 2.3.4

Parameters

The io.seek() function is used to move the current read/write position.

Notice: other read standard seek bases (like "cur", "end") are not supported.

Parameters

• file object a file object that was returned by the io.open() function.

• offset position the read/write file pointer at the specified offset from the beginning of the file. If specified offset is bigger than the file size, then the pointer is moved to the end of the file.

Return value

• 0 success

• <number> any other value means failure.

Returns the value of a source.

The list of fixed sources:

In OpenTX 2.1.x the telemetry sources no longer have a predefined name. To get a telemetry value simply use it's sensor name. For example:

• Altitude sensor has a name "Alt"

• to get the current altitude use the source "Alt"

• to get the minimum altitude use the source "Alt-", to get the maximum use "Alt+"

@status current Introduced in 2.0.0, changed in 2.1.0, Cels+ and Cels- added in 2.1.9

Parameters

• source can be an identifier (number) (which was obtained by the getFieldInfo())

  or a name (string) of the source.

Return value

• value current source value (number). Zero is returned for:

  • non-existing sources

  • for all telemetry source when the telemetry stream is not received

Notice

Getting a value by its numerical identifier is faster then by its name. While Cels sensor returns current values of all cells in a table, a Cels+ or Cels- will return a single value - the maximum or minimum Cels value.

Returns the value of a source. Supersedes getValue.

The list of fixed sources:

In OpenTX 2.1.x the telemetry sources no longer have a predefined name. To get a telemetry value simply use it's sensor name. For example:

• Altitude sensor has a name "Alt"

• to get the current altitude use the source "Alt"

• to get the minimum altitude use the source "Alt-", to get the maximum use "Alt+"

value is nil for non-existing sources. all non-allowed sensors while FAI MODE is active, or if a telemetry item value has never been received

value is a table for GPS position:

• lat (number) latitude, positive is North

• lon (number) longitude, positive is East

• pilot-lat

value is a table for date/time, see getDateTime()

value is a table for battery cells(except where no cells were detected in which case the returned value is 0):

• table has one item for each detected cell:

• key (number) cell number (1 to number of cells)

• value (number) current cell voltage

@status current Introduced in 2.8.0

Parameters

• source can be an index (number) (which was obtained by getFieldInfo or getSourceIndex) or a name (string) of the source.

Return value

• value current source value (number), or last known telemetry item value.

• isCurrent is true for telemetry sources that are within the "Sensor Lost" duration and telemetry is streaming . Always true for non-telemetry items.

• isFresh

Notice

Getting a value by its numerical identifier is much faster than by its name. While Cels sensor returns current values of all cells in a table, a Cels+ or Cels- will return a single value - the maximum or minimum Cels value.

WARNING - Running a One-Time script will suspend execution of all other currently loaded Lua scripts (Custom, Telemetry, and Functions)

Overview

One-Time scripts start when called upon by a specific radio function or when the user selects them from a contextual menu. They do their task and are then terminated and unloaded. Please note that all persistent scripts are halted during the execution of One-Time scripts. They are automatically restarted once the One-Time script is finished. This is done to provide enough system resources to execute the One-Time script.

Lifetime

Script is executed when user selects Execute on a script file from SD card browser screen, or opens a Lua Tool, or creates a new model with a Wizard script.

The script executes until:

• it returns value different from 0

• is forcefully closed by user by long press of EXIT key

• is forcefully closed by system if it misbehaves (e.g. run-time error or low

  memory)

File Location

General One-Time scripts can be placed anywhere on SD card, however, the folder /SCRIPTS/ is recommended.

Tool scripts must be stored in /SCRIPTS/TOOLS.

Wizard scripts must be stored in the same subfolder of /TEMPLATES/ with the same "first name" as the template file using it. Some Wizard scripts are just small scripts that load one of the common scripts located in /SCRIPTS/WIZARD/.

Interface

Every script must include a return statement at the end, defining its interface to EdgeTX. This statement returns a table with the following fields:

• init function (optional)

• run function

Example

Notes:

• The event parameter indicates which transmitter key has been pressed (see ).

• The touchState value is only present when event is a touch event (see ).

Introduction

Lua was chosen for OpenTX, and hence also EdgeTX, because it is a small language designed to be highly extensible by libraries written in C and C++, so it can be integrated into other systems like EdgeTX. It is also relatively efficient, both in terms of memory and CPU usage, and hence well suited for the radios.

In addition to the provided libraries, Lua has a very elegant mechanism for loading new Lua code modules during run-time. A lot of the elegance comes from the way that the loading mechanism meshes with another concept supported by Lua: first class functions with closures.

First Class Functions

Computer science pioneer Christopher Strachey introduced the concept of functions as first-class objects in his paper from 1967. What it means is that functions can be treated as other variables: as arguments passed in function calls, as results returned from function calls, and a function identifier can be re-assigned to another chunk of function code, just like a variable ca be assigned to a new value.

In Lua, a function declaration is really "syntactic sugar" for assigning a variable to the chunk of code that is called when the function is invoked, i.e.

local function f(x) return x + 1 end

is the same as

local f = function(x) return x + 1 end

You can even add functions to Lua tables, i.e.

t = { f = f }

will add the above function to the table t, as a field that is also called f. Does that look familiar to the return statement required at the end of a Lua script?

Yes indeed, because a script is really an anonymous function that returns a list of functions to the system. The function declarations assign variables to chunks of function code, these variables are added to the list returned at the end of the script, and the system then calls the functions periodically to run the script. So the script itself is run one time initially, and subsequently the functions returned by the last statement are called periodically.

Closures

Another important concept that goes with first-class functions, is closures. This is the environment of the function with the variable names that the function can see. Please consider the following function counter that returns another function:

The function is returned directly without being assigned to a variable name. The closure of the function returned is the body of the function counter, containing both the arguments start and step, and the local variable x. So if c1 = counter(1, 1) then c1() will return 1, 2, 3, ... when called repeatedly, and if c2 = counter(2, 3) then c2() will return 2, 5, 8, ...

Likewise, the local variables that you declare outside the functions of your script can be used by all of the functions in your script, and they persist between function calls, but they are not visible to other scripts.

The are a little trickier, as you can register multiple instances of the same widget script, and all of these instances run within the same Lua closure. Therefore, local variables declared outside any functions in a widget script are shared among all of the instances of that script. But each call to the create(...) function returns a new widget list to the system. And since this list is unique to each instance, you can add private instance variables to it.

Functions with Variable Number of Arguments

Please consider this function:

It takes an argument x and a list ... A vararg list is just like a list of arguments separated by commas, and you can call the function with any number of arguments greater than 1. Inside the function, you can also treat ... like a comma separated list of variables, e.g. in the above function, ... is converted to a table by {...} just like you could construct a table by e.g. {a, b, c}. The table is iterated with the ipairs function to look for an element matching the first argument x. So e.g. the following statement

if event == EVT_VIRTUAL_ENTER or event == EVT_VIRTUAL_EXIT then

can be replaced by

if match(event, EVT_VIRTUAL_ENTER, EVT_VIRTUAL_EXIT) then

You can also use ... directly as a comma separated list of values, e.g. local a, b, c = ... will assign the three variables to the three first arguments following x, or nil if none are given.

References

The helpful, both if you want to learn more about Lua, and if you want to search for answers to specific questions.

Flags

There are two types of color constants: one that is an index into a table holding a palette of theme colors, and one that is just a color.

Indexed colors

These are the theme colors plus CUSTOM_COLOR, and they can be changed with the function lcd.setColor(color_index, color). Please note: if an indexed color is changed, then it changes everywhere that it is used. For the theme colors, this is not only in other widgets, but everywhere throughout the radio's user interface!

This section includes Acknowledgments and Getting Started.

The key event mechanism

Each time a key is pressed, held and released a number of events get generated. Here is a typical flow:

Overview

Most of the time, widget scripts show some info in a zone either in the top bar or in one of the user defined main views, and they cannot receive direct input from the user via key events like e.g. Telemetry scripts.

But widgets on the main views can also be shown in full screen mode, where they take over the entire screen area. And here they receive user input via key events, and for radios with touch screen, also touch events. Full screen mode can be entered by selecting the widget, pressing ENTER and selecting Full screen on the widget menu, or by double tapping the widget on radios with a touch screen. Full screen mode can be exited by long pressing the RETURN button, or by calling the Lua function lcd.exitFullScreen().

Each model can have up to five main views, with up to 8 widgets per screen, depending on their size and layout. Each instance of a widget has his own options table.

Please note: Widget scripts are only available on radios with color screens, e.g. FrSky Horus models, Radiomaster TX16 and Jumper T16.

Lifetime

All widget scripts on the SD card are loaded into memory when the model is selected; even widgets that are not used. This has the side effect that any global functions defined in a widget script will always be available to other widget scripts. It also means that any script on the SD card will consume part of the radio's memory - even if it is not being used. Therefore, it is important to either keep widget scripts small, or to use Lua's loadScript() function to load code dynamically.

They can be added to the top bar or a main view through the telemetry setup menu. When a widget has been added to a screen, then the widget functions are called as follows:

• create is called once when the widget instance is registered (started).

• update is called when widget settings are changed by the user.

• background

File Location

Widgets are located on the SD card, each in their specific folder /WIDGETS/<name>/main.lua (<name> must be in 8 characters or less).

Interface

Every script must include a return statement at the end, defining its interface to EdgeTX. This statement returns a table with the following fields:

• name string

• options table

• create function

Example

Notes

• The name must be max. 10 characters long.

• options is passed to create and then stored in Lua. Changing it has no effect on EdgeTX.

WARNING - Do not use Lua Custom scripts for controlling any aspect of your model that could cause a crash if the script stops executing!

Overview

Each model can have several custom scripts associated with it, and these scripts are run periodically. They behave similarly to standard OpenTX mixers, but at the same time they provide a much more flexible and powerful tool. Custom scripts take one or more values as inputs, do some processing in Lua code, and output one or more values.

Please note: the firmware must be compiled with the option LUA_MIXER=Y for Custom scripts to be available.

Please note: the scripts should be as short as possible, to avoid delays. It is also important to keep in mind that other loaded Telemetry and Function scripts can add to the response time, or worse: hang the system!

Typical uses

• replacement for complex mixes that are not critical to model function

• complex processing of inputs and reaction to their current state and/or their history

• filtering of telemetry values

Limitations

• cannot update LCD screen or perform user input.

• should not exceed allowed run-time/ number of instructions.

• custom scripts are run with less priority than built-in mixes. Their execution period is around 30ms and is not guaranteed!

Lifetime

• Custom scripts are loaded from SD card when model is selected

• init __function is called first

• run function is called periodically (about 30 times per second)

Disabled script

If the script output is used as a mixer source , and the script is killed for whatever reason, then the whole mixer line is disabled ! This can be used for example to provide a fallback in case Lua Custom script is killed.

Example where Lua mix script is used to drive ailerons in some clever way, but control falls back to the standard aileron mix if script is killed. Second mixer line replaces the first one when the script is alive:

File Location

Place them on SD card in folder /SCRIPTS/MIXES/. File name length (without extension) must be 6 characters or less (this limit was 8 characters in OpenTX 2.1).

Interface

Every script must include a return statement at the end, defining its interface to EdgeTX. This statement returns a table with the following fields:

• input table (optional)

• output table (optional)

• init function (optional)

Example

Input table

The input table defines what values are available as input(s) to custom scripts. There are two forms of input table entries.

SOURCE inputs provide the current value of a selected OpenTX variable. The source must be selected by the user when the script is configured. Source can be any value that EdgeTX knows about (inputs, channels, telemetry values, switches, custom functions etc.). Note: the typical input range is -1024 thru +1024. Simply divide the input value by 10.24 to convert to a percentage from -100% to +100%.

VALUE inputs provide a constant value that is set by the user when the script is configured.

• name - maximum length of 8 characters

• min - minimum value of -128

• max - maximum value of 127

Output table