# Basics

## Conventions

- 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.
- 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()')
end
```

### 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.

# Function Reference

## Utility

### `print(msg)`

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

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

### `setTickRate(hz)`

Sets the rate at which rusEFI calls your `onTick` function, in hz.

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

### `table3d(tableIdx, x, y)`

Looks up a value from the specified FSIO table.

- Parameters
  - `tableIdx`: Index of the table to use.  Currently 4 tables are supported, so indices 0, 1, 2, and 3 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.

## Input

### `getSensor(index)`

Reads the specified sensor.

- Parameters
  - `index`: Index of the sensor to read.  [A list of sensor indices can be found here.](https://github.com/rusefi/rusefi/blob/master/firmware/controllers/sensors/sensor_type.h)
- Returns
  - A reading from the sensor, or `nil` if the sensor has a problem or isn't configured.

### `getSensorRaw(index)`

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.](https://github.com/rusefi/rusefi/blob/master/firmware/controllers/sensors/sensor_type.h)
- 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.

### `hasSensor(index)`

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

- Parameters
  - `index`: Index of the sensor to check.  [A list of sensor indices can be found here.](https://github.com/rusefi/rusefi/blob/master/firmware/controllers/sensors/sensor_type.h)
- Returns
  - A boolean value, `true` if the sensor is configured, and `false` if not.


### `getAnalog(index)`

Reads an analog voltage from one of the FSIO ADC inputs.

- Parameters
  - `index`: The index of the configured analog input to read. Currently 4 inputs are supported, so values of 0, 1, 2, 3 are valid for this parameter.
- Returns
  - The raw analog voltage from the input pin. Most rusEFI ECUs can measure between 0 and 5 volts, so this value will be a number between 0 and 5.

### `getDigital(index)`

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 |


## Output

coming soon...