nodemcu-firmware/docs/en/modules/tmr.md

Timer Module

Since	Origin / Contributor	Maintainer	Source
2014-12-12	Zeroday	dnc40085	tmr.c

The tmr module allows access to simple timers, the system counter and uptime.

It is aimed at setting up regularly occurring tasks, timing out operations, and provide low-resolution deltas.

What the tmr module is not however, is a time keeping module. While most timeouts are expressed in milliseconds or even microseconds, the accuracy is limited and compounding errors would lead to rather inaccurate time keeping. Consider using the rtctime module for "wall clock" time.

NodeMCU provides 7 timers, numbered 0-6. It is currently up to the user to keep track of which timers are used for what.

tmr.alarm()

This is a convenience function combining tmr.register() and tmr.start() into a single call.

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

Parameters

• id timer id (0-6)
• interval_ms timer interval in milliseconds. Maximum value is 12884901. In SDKs <= 1.5.0 values >6871948 result in incorrect behaviour.
• mode timer mode:
  • tmr.ALARM_SINGLE a one-shot alarm (and no need to call tmr.unregister())
  • tmr.ALARM_SEMI manually repeating alarm (call tmr.start() to restart)
  • tmr.ALARM_AUTO automatically repeating alarm

Returns

true if the timer was started, false on error

Example

if not tmr.alarm(0, 5000, tmr.ALARM_SINGLE, function() print("hey there") end) then print("whoopsie") end

See also

• tmr.register()
• tmr.start()
• tmr.unregister()

tmr.delay()

Busyloops the processor for a specified number of microseconds.

This is in general a bad idea, because nothing else gets to run, and the networking stack (and other things) can fall over as a result. The only time tmr.delay() may be appropriate to use is if dealing with a peripheral device which needs a (very) brief delay between commands, or similar. Use with caution!

Also note that the actual amount of time delayed for may be noticeably greater, both as a result of timing inaccuracies as well as interrupts which may run during this time.

Syntax

tmr.delay(us)

Parameters

us microseconds to busyloop for

Returns

nil

Example

tmr.delay(100)

tmr.interval()

Changes a registered timer's expiry interval.

Syntax

tmr.interval(id, interval_ms)

Parameters

• id timer id (0-6)
• interval_ms new timer interval in milliseconds. Maximum value is 12884901. In SDKs <= 1.5.0 values >6871948 result in incorrect behaviour.

Returns

nil

Example

tmr.register(0, 5000, tmr.ALARM_SINGLE, function() print("hey there") end)
tmr.interval(0, 3000) -- actually, 3 seconds is better!

tmr.now()

Returns the system counter, which counts in microseconds. Limited to 31 bits, after that it wraps around back to zero. That is essential if you use this function to debounce or throttle GPIO input.

Syntax

tmr.now()

Parameters

none

Returns

the current value of the system counter

Example

print(tmr.now())
print(tmr.now())

tmr.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.unregister() on it. For one-shot timers this is not necessary, unless they were stopped before they expired.

Syntax

tmr.register(id, interval_ms, mode, func)

Parameters

• id timer id (0-6)
• interval_ms timer interval in milliseconds. Maximum value is 12884901. In SDKs <= 1.5.0 values >6871948 result in incorrect behaviour.
• mode timer mode:
  • tmr.ALARM_SINGLE a one-shot alarm (and no need to call tmr.unregister())
  • tmr.ALARM_SEMI manually repeating alarm (call tmr.start() to restart)
  • tmr.ALARM_AUTO automatically repeating alarm

Note that registering does not start the alarm.

Returns

nil

Example

tmr.register(0, 5000, tmr.ALARM_SINGLE, function() print("hey there") end)
tmr.start(0)

See also

tmr.alarm()

tmr.softwd()

Provides a simple software watchdog, which needs to be re-armed or disabled before it expires, or the system will be restarted.

Syntax

tmr.softwd(timeout_s)

Parameters

timeout_s watchdog timeout, in seconds. To disable the watchdog, use -1 (or any other negative value).

Returns

nil

Example

function on_success_callback()
  tmr.softwd(-1)
  print("Complex task done, soft watchdog disabled!")
end

tmr.softwd(5)
-- go off and attempt to do whatever might need a restart to recover from
complex_stuff_which_might_never_call_the_callback(on_success_callback)

tmr.start()

Starts or restarts a previously configured timer.

Syntax

tmr.start(id)

Parameters

id timer id (0-6)

Returns

true if the timer was started, false on error

Example

tmr.register(0, 5000, tmr.ALARM_SINGLE, function() print("hey there") end)
if not tmr.start(0) then print("uh oh") end

See also

• tmr.register()
• tmr.stop()
• tmr.unregister()

tmr.state()

Checks the state of a timer.

Syntax

tmr.state(id)

Parameters

id timer id (0-6)

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

running, mode = tmr.state(0)

tmr.stop()

Stops a running timer, but does not unregister it. A stopped timer can be restarted with tmr.start().

Syntax

tmr.stop(id)

Parameters

id timer id (0-6)

Returns

true if the timer was stopped, false on error

Example

if not tmr.stop(2) then print("timer 2 not stopped, not registered?") end

See also

• tmr.register()
• tmr.stop()
• tmr.unregister()

tmr.time()

Returns the system uptime, in seconds. Limited to 31 bits, after that it wraps around back to zero.

Syntax

tmr.time()

Parameters

none

Returns

the system uptime, in seconds, possibly wrapped around

Example

print("Uptime (probably):", tmr.time())

tmr.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

tmr.unregister(id)

Parameters

id timer id (0-6)

Returns

nil

Example

tmr.unregister(0)

See also

tmr.register()

tmr.wdclr()

Feed the system watchdog.

In general, if you ever need to use this function, you are doing it wrong.

The event-driven model of NodeMCU means that there is no need to be sitting in hard loops waiting for things to occur. Rather, simply use the callbacks to get notified when somethings happens. With this approach, there should never be a need to manually feed the system watchdog.

Syntax

tmr.wdclr()

Parameters

none

Returns

nil