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.

Attention

NodeMCU formerly provided 7 static timers, numbered 0-6, which could be used instead of OO API timers initiated with tmr.create(). After a long period of deprecation, these were removed in 2019 Q1.

tmr.create()

Creates a dynamic timer object; see below for its method table.

Dynamic timer can be used instead of numeric ID in control functions. Also can be controlled in object-oriented way.

Functions supported in timer object:

Parameters

none

Returns

timer object

Example

local mytimer = tmr.create()
mytimer:register(5000, tmr.ALARM_SINGLE, function (t) print("expired"); t:unregister() end)
mytimer:start()

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.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.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.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.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

tmr.ccount()

Get value of CPU CCOUNT register which contains CPU ticks. The register is 32-bit and rolls over.

Converting the register's CPU ticks to us is done by dividing it to 80 or 160 (CPU80/CPU160) i.e. tmr.ccount() / node.getcpufreq().

Register arithmetic works without need to account for roll over, unlike tmr.now(). Because of same reason when CCOUNT is having its 32nd bit set, it appears in Lua as negative number.

Syntax

tmr.ccount()

Returns

The current value of CCOUNT register.

Example

function timeIt(fnc, cnt)
   local function loopIt(f2)
     local t0 = tmr.ccount()
     for i=1,cnt do
       f2()
     end
     local t1 = tmr.ccount()
     return math.ceil((t1-t0)/cnt)
   end
   assert(type(fnc) == "function", "function to test missing")
   cnt = cnt or 1000
   local emptyTime = loopIt(function()end)
   local deltaCPUTicks = math.abs(loopIt(fnc) - emptyTime)
   local deltaUS = math.ceil(deltaCPUTicks/node.getcpufreq())
   return deltaCPUTicks, deltaUS
end

print( timeIt(function() tmr.ccount() end) )

Timer Object Methods

tobj:alarm()

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

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

Syntax

tobj: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 unregister())
    • tmr.ALARM_SEMI manually repeating alarm (call start() 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

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

See also

tobj:interval()

Changes a registered timer's expiry interval.

Syntax

tobj:interval(interval_ms)

Parameters

  • interval_ms new timer interval in milliseconds. Maximum value is 6870947 (1:54:30.947).

Returns

nil

Example

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

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

Syntax

tobj: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 tobj:unregister())
    • tmr.ALARM_SEMI manually repeating alarm (call tobj:start() 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

mytimer = tmr.create()
mytimer:register(5000, tmr.ALARM_SINGLE, function() print("hey there") end)
mytimer:start()

See also

tobj:start()

Starts or restarts a previously configured timer.

Syntax

tobj:start()

Parameters

None

Returns

true if the timer was started, false on error

Example

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

tobj:state()

Checks the state of a timer.

Syntax

tobj: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

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

tobj:stop()

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

Syntax

tobj:stop()

Parameters

None

Returns

true if the timer was stopped, false on error

Example

mytimer = tmr.create()
if not mytimer:stop() then print("timer not stopped, not registered?") end

See also

tobj: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

tobj:unregister()

Parameters

None

Returns

nil

See also

tobj:register()