nodemcu-firmware/docs/modules/tmr.md

# Timer Module
| Since  | Origin / Contributor  | Maintainer  | Source  |
| :----- | :-------------------- | :---------- | :------ |
| 2014-12-12 | [Zeroday](https://github.com/funshine) |              [dnc40085](https://github.com/dnc40085) | [tmr.c](../../components/modules/tmr.c)|

The tmr module allows access to simple timers. It is aimed at setting up regularly occurring tasks and timing out operations.

What the tmr module is *not* however, is a time keeping module. While all timeouts are expressed in milliseconds, the accuracy is limited and compounding errors would lead to rather inaccurate time keeping. A module for "wall clock" time is not yet available.

!!! note

    The resolution of the timers is determined by FreeRTOS' tick rate. The default rate of 100 kHz (resulting in 10 ms resolution) can be changed with `make menuconfig` at item `Component config ---> FreeRTOS ---> Tick rate (Hz)`.

## tmr.create()

Creates a dynamic timer object.

#### Syntax
`tmr.create()`

#### Parameters
none

#### Returns
`timer` object

#### Example
```lua
local mytimer = tmr.create()

-- oo calling
mytimer:register(5000, tmr.ALARM_SINGLE, function (t) print("expired") end)
mytimer:start()
mytimer = nil
```

# tmr Object
## tmr.obj:alarm()

This is a convenience function combining [`tmr.obj:register()`](#tmrobjregister) and [`tmr.obj:start()`](#tmrobjstart) into a single call.

To free up the resources with this timer when done using it, call [`tmr.obj:unregister()`](#tmrobjunregister) on it. For one-shot timers this is not necessary, unless they were stopped before they expired.

#### Syntax
`mytmr:alarm(interval_ms, mode, func())`

#### Parameters
- `interval_ms` timer interval in milliseconds. Maximum value is 6870947 (1:54:30.947).
- `mode` timer mode:
	- `tmr.ALARM_SINGLE` a one-shot alarm (and no need to call [`tmr.unregister()`](#tmrunregister))
	- `tmr.ALARM_SEMI` manually repeating alarm (call [`tmr.start()`](#tmrstart) to restart)
	- `tmr.ALARM_AUTO` automatically repeating alarm
- `func(timer)` callback function which is invoked with the timer object as an argument

#### Returns
`true` if the timer was started, `false` on error

#### Example
```lua
if not tmr.create():alarm(5000, tmr.ALARM_SINGLE, function()
  print("hey there")
end)
then
  print("whoopsie")
end
```
#### See also
- [`tmr.create()`](#tmrcreate)
- [`tmr.obj:register()`](#tmrobjregister)
- [`tmr.obj:start()`](#tmrobjstart)
- [`tmr.obj:unregister()`](#tmrobjunregister)

## tmr.obj:interval()

Changes a registered timer's expiry interval.

#### Syntax
`mytmr:interval(interval_ms)`

#### Parameters
- `interval_ms` new timer interval in milliseconds. Maximum value is 6870947 (1:54:30.947).

#### Returns
`nil`

#### Example
```lua
mytimer = tmr.create()
mytimer:register(10000, tmr.ALARM_AUTO, function() print("hey there") end)
mytimer:interval(3000) -- actually, 3 seconds is better!
mytimer:start()
```

## tmr.obj:register()

Configures a timer and registers the callback function to call on expiry.

To free up the resources with this timer when done using it, call [`tmr.obj:unregister()`](#tmrobjunregister) on it. For one-shot timers this is not necessary, unless they were stopped before they expired.

#### Syntax
`mytmr:register(interval_ms, mode, func())`

#### Parameters
- `interval_ms` timer interval in milliseconds. Maximum value is 6870947 (1:54:30.947).
- `mode` timer mode:
	- `tmr.ALARM_SINGLE` a one-shot alarm (and no need to call [`tmr.unregister()`](#tmrunregister))
	- `tmr.ALARM_SEMI` manually repeating alarm (call [`tmr.start()`](#tmrunregister) to restart)
	- `tmr.ALARM_AUTO` automatically repeating alarm
- `func(timer)` callback function which is invoked with the timer object as an argument

Note that registering does *not* start the alarm.

#### Returns
`nil`

#### Example
```lua
mytimer = tmr.create()
mytimer:register(5000, tmr.ALARM_SINGLE, function() print("hey there") end)
mytimer:start()
```
#### See also
- [`tmr.create()`](#tmrcreate)
- [`tmr.obj:alarm()`](#tmrobjalarm)

## tmr.obj:start()

Starts or restarts a previously configured timer.

#### Syntax
`mytmr:start()`

#### Parameters
none

#### Returns
`true` if the timer was started, `false` on error

#### Example
```lua
mytimer = tmr.create()
mytimer:register(5000, tmr.ALARM_SINGLE, function() print("hey there") end)
if not mytimer:start() then print("uh oh") end
```
#### See also
- [`tmr.create()`](#tmrcreate)
- [`tmr.obj:register()`](#tmrobjregister)
- [`tmr.obj:stop()`](#tmrobjstop)
- [`tmr.obj:unregister()`](#tmrobjunregister)

## tmr.obj:state()

Checks the state of a timer.

#### Syntax
`mytmr:state()`

#### Parameters
none

#### Returns
(bool, int) or `nil`

If the specified timer is registered, returns whether it is currently started and its mode. If the timer is not registered, `nil` is returned.

#### Example
```lua
mytimer = tmr.create()
print(mytimer:state()) -- nil
mytimer:register(5000, tmr.ALARM_SINGLE, function() print("hey there") end)
running, mode = mytimer:state()
print("running: " .. tostring(running) .. ", mode: " .. mode) -- running: false, mode: 0
```

## tmr.obj:stop()

Stops a running timer, but does *not* unregister it. A stopped timer can be restarted with [`tmr.obj:start()`](#tmrobjstart).

#### Syntax
`mytmr:stop()`

#### Parameters
none

#### Returns
`true` if the timer was stopped, `false` on error

#### Example
```lua
mytimer = tmr.create()
if not mytimer:stop() then print("timer not stopped, not registered?") end
```
#### See also
- [`tmr.obj:register()`](#tmrobjregister)
- [`tmr.obj:stop()`](#tmrobjstop)
- [`tmr.obj:unregister()`](#tmrobjunregister)

## tmr.obj:unregister()

Stops the timer (if running) and unregisters the associated callback.

This isn't necessary for one-shot timers (`tmr.ALARM_SINGLE`), as those automatically unregister themselves when fired.

#### Syntax
`mytmr:unregister()`

#### Parameters
none

#### Returns
`nil`

#### See also
[`tmr.obj:register()`](#tmrobjregister)


## tmr.wdclr()

Resets the watchdog timer to prevent a reboot due to a perceived hung task.

Use with caution, as this could prevent a reboot to recover from a
genuinely hung task.

On the ESP32, the `tmr.wdclr()` function is implemented as a task yield
to let the system "IDLE" task do the necessary watchdog maintenance.
Overuse of this function is likely to result in degraded performance.

#### Syntax
`tmr.wdclr()`

#### Parameters
none

#### Returns
`nil`

#### Example
```lua
function long_running_function()
  while 1
  do
    if some_condition then break end
    -- do some heavy calculation here, for example
    tmr.wdclr()
  end
end
```