Lua Scripting


A proper ECU has to offer users as much flexibility as possible, meaning a completely user-defined control strategy for both primary and auxiliary actuators. For many years rusEFI had FSIO to do just that.

As of 2022, rusEFI has replaced FSIO with a popular open source Lua scripting engine We use Lua version 5.4.3


  • The Lua interpreter will trigger an error if there is a mistake in the program, check the rusEFI console to see errors and script output.
  • Unless otherwise mentioned, all index parameters start with the first element at index at 0.

Writing Your Script

The entire Lua script is read at startup, then a function called onTick is called periodically by rusEFI.

Here is a simple script you can run to illustrate this behavior:

print('Hello Lua startup!')

function onTick()
    print('Hello onTick()')

Controlling the Tick Rate

The function setTickRate(hz) can be used to configure how often rusEFI calls the onTick function. If your script does a lot of work in the onTick() function it may run slower than the desired rate. Since the Lua virtual machine runs at low priority compared to other functions of the ECU, it is impossible to swamp the ECU with too much Lua work, so set the tick rate to whatever is necessary. onCanRx runs at the same rate as onTick

n = 0
setTickRate(5) --set tick rate to 5hz
function onTick()
    print('Hello Lua: ' ..n)
    n = n + 1

Function Reference

User Settings


For example getOutput("clutchUpState") getOutput("brakePedalState")

See for output names.



Use setBrakePedalState to tell rusEFI about CAN-based brake pedal.


Use setAcRequestState to tell rusEFI about CAN-based A/C request.


Disable/supress A/C functionality regardless of what and how enables it, an override kind of deal.



Gets current calibration value for specified scalar setting. For example getCalibration("cranking.rpm")

See for field names.

setCalibration(name, value, needEvent)

Sets specified calibration setting to specified value. Fires calibration change event depending on needEvent parameter.

For example setCalibration("cranking.rpm", 900, false)

findSetting(name, defaultValue)

Find User Setting with specified name and returns numeric value. Useful when script developer and script consumer are different people, also useful while Lua script editing is available only in TS.

  • Parameters
  • name: Variable name, as in corresponding 'name' field in configuration
  • dataultValue: value to use if specified setting not located by name

Engine Control



setSparkSkipRatio(0) to skip 0% of the ignition events, i.e. no skipping setSparkSkipRatio(0.5) would skip half of ignition events. We never skip two consecutive ignitions.



Sorry not finished :(


Sorry not finished :(


Additive for closed loop target boost pressure.


Multiplier for closed loop target boost pressure.


todo add details but ready to test!


todo add details but ready to test!


extraEtb 10 for 10%

CAN bus


enabled by default

use enableCanTx(false) to suppress CAN TX

txCan(bus, ID, isExt, payload)

  • Parameters
  • bus: hardware CAN bus index, only '1' on most rusEFI boards, '1' or '2' on Proteus
  • isExt: 0 for 11 bit mode


canRxAdd(bus, id)

canRxAdd(id, callback)

canRxAdd(bus, id, callback)

canRxAddMask(id, mask)

canRxAddMask(bus, id, mask)

canRxAddMask(id, mask, callback)

canRxAddMask(bus, id, mask, callback)

  • Parameters
  • id: CAN ID to listen to.
  • mask: Apply a mask to the received ID before comparing to the id parameter. For example, passing an id of 3 and mask of 0xFF will match any frame whose last 8 bits match 3. If omitted, no masking is applied before comparison, so only a single CAN ID will be received. Use the mask to subscribe to multiple messages with similar IDs with a single call to canRxAddMask.
  • bus: Hardware CAN bus index, only '1' on most rusEFI boards, '1' or '2' on Proteus. If this parameter is omitted, messages will be received from any bus.
  • callback: A the callback function to call when the specified ID is received. If this parameter is not passed, the default function onCanRx will be used.

Your CAN RX callback should look like this:

function onCanRx(bus, id, dlc, data)
    -- Do things with CAN data!



Print a line of text to the ECU's log.

  • Parameters
  • msg: The message to print. Pass a string or number and it will be printed to the log.
  • Returns
  • none

Usage example


n = 5.5
print('Hello Lua, number is: ' ..n)

Output: Hello Lua, number is 5.5


Sets the rate at which rusEFI calls your onTick and onCanRx functions, in hz. On reset default is 10hz.

  • Parameters
  • hz: Desired tick rate, in hz. Values passed will be clamped to a minimum of 1hz, and maximum of 100hz.
  • Returns
  • none


Stops MCU.

interpolate(x1, y1, x2, y2, x)

Interpolates x placing it on the line defined by (x1, y1) and (x2, y2)


Find table index by specified human-readable name.

table3d(tableIdx, x, y)

Looks up a value from the specified Script Table.

  • Parameters
  • tableIdx: Index of the table to use. Currently 4 tables are supported, so indices 1, 2, 3, and 4 are valid.
  • x: X-axis value to look up in the table (this is often RPM)
  • y: Y-axis value to look up in the table (this is often load)
  • Returns
  • A number representing the value looked up from the table.


Finds curve index by specific curve name

curve(curveIdx, x)

Looks up a value from the specified Script Curve. - Parameters - tableIdx: Index of the script to use, starting from 1. - x: Axis value to look up in the table

setDebug(index, value)

Sets a debug channel to the specified value. Note: this only works when the ECU debug mode is set to Lua.

  • Parameters
  • index: the index of the debug channel to set, 1 thru 7 inclusive.
  • value: the value to set the channel to
  • Returns
  • none


Puts MCU into standby low current consumption mode.



Reads the specified sensor.


Reads the specified sensor.


Reads the raw value from the specified sensor. For most sensors, this means the analog voltage on the relevant input pin.

  • Parameters
  • index: Index of the sensor to read. A list of sensor indices can be found here.
  • Returns
  • The raw value that yielded the sensor reading, or 0 if the sensor doesn't support raw readings, isn't configured, or has failed.


More or less like getSensorRaw but always voltage of aux analog input.

  • Parameters
  • index: Index of aux analog sensor to read. From 0 to 3
  • Returns
  • Voltage of sensor reading, or nil if sensor isn't configured.


Checks whether a particular sensor is configured (whether it is currently valid or not).


Reads a digital input from the specified channel.

  • Parameters
  • index: The index of the digital channel to read. See table below for values.
  • Returns
  • A boolean value representing the state of the input pin. true = high voltage (above ~2 volts), false = low voltage (below ~3 volts)

Valid index parameter values:

Index Channel Name
0 Clutch down switch
1 Clutch up switch
2 Brake switch
3 AC switch


Reads physical value of arbitrary MCU pin - Parameters - pinName: string name of MCU pin, for examples "PD15"


startPwm(index, frequency, duty)

Initializes PWM on the specified index, starting at the specified frequency and duty cycle. The index selects which config field pin to use, see "Lua PWM Outputs" page in TunerStudio.

  • Parameters
  • index: The index of the PWM channel to start. Valid values are 0 through 7, one for each of the 8 channels.
  • frequency: Initial frequency of the output, in hertz (cycles per second). Valid values are between 1 and 1000hz.
  • duty: Initial duty cycle of the output. 0.0 = fully off, and 1.0 = fully on. 0.25 = on 25% of the time, off 75% of the time.
  • Returns
  • none

setPwmDuty(index, duty)

Set the duty cycle of the specified PWM channel.

  • Parameters
  • index: The index of the PWM channel to set. Valid values are 0 through 7, one for each of the 8 channels.
  • duty: Desired duty cycle of the output. 0.0 = fully off, and 1.0 = fully on. 0.25 = on 25% of the time, off 75% of the time.
  • Returns
  • none

setPwmFreq(index, frequency)

  • Parameters
  • index: The index of the PWM channel to set.
  • frequency: Initial frequency of the output, in hertz (cycles per second). Valid values are between 1 and 1000hz.
  • Returns
  • none

Misc console commands





t =;
timingAdd = 0;

function onTick()
   auxV = getAuxAnalog(0)
   tps = getSensor("TPS")
-- todo: check for NIL value which is a sign of analog input not assigned in TS
   if auxV > 2 then

   val = t:getElapsedSeconds();

   if t:getElapsedSeconds() < 3 then
     timingAdd = 10;
     timingAdd = 0;

   print('Hello analog ' .. auxV .. " " .. val)


-- index 0, 100Hz, zero duty inititally
startPwm(0, 100, 0)

function onTick()
 enable_pump = getSensor("RPM") > 700  and getSensor("BatteryVoltage") > 13 and getSensor("VehicleSpeed") <60

 -- lua does not have ternary ? : operator, this here means "1 if enable_pump and 0 otherwise"
 setPwmDuty(0, enable_pump and 1 or 0)


CAN transmit

function onTick()
  tps = getSensor("CLT")
  print('TPS ' .. tps)
  voltage0 = getSensor("aux0")

  txPayload = {}
  // first byte: integer part, would be autoboxed to int
  txPayload[1] = voltage0
  // second byte: fractional part, would be autoboxed to int, overflow would be ignored
  txPayload[2] = voltage0 * 256;

  txCan(1, 0x600, 1, txPayload)


set sensor value

vssSensor ="VehicleSpeed")
function onTick()
    vssSensor : set(90)
    val = getSensor("VehicleSpeed")
    print ("VSS " .. val)

CAN receive

function onCanRx(bus, id, dlc, data)
    print('got CAN id=' ..' dlc=' ..dlc)
    id11 = id % 2048
    if id11 == 0x500 then
        -- Check can state of BCM
        canState = data[1]
    if id11 == 0x570 then
function decimalToHex(num)
    if num == 0 then
        return '0'

    local hexstr = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "A", "B", "C", "D", "E", "F" }
    local result = ""
    while num > 0 do
        local n = num % 16
        result = hexstr[n + 1] ..result
        num = math.floor(num / 16)
    return result

function print_array(arr)
    local str = ""
    local index = 1
    while arr[index] ~= nil do
        str = str.." "..decimalToHex(arr[index])
        index = index + 1
    return str


tableIndex = findTableIndex("duty")

TurbochargerSpeed = getSensor("TurbochargerSpeed")
tps = getSensor("Tps1")

dutyCycle = table3d(tableIndex, TurbochargerSpeed, tps)

sparkCutCurve = findCurveIndex("sparkcut")
sparkCutByTorque = curve(sparkCutCurve, torque)

See also

BMW iDrive


More examples at

See also a library for CAN data manipulation

See also test driven development approach

Lua Ternary Operator