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1. 

   General Tree
   Member

   Hi everyone.

   Iv'e been playing with the timers, and saw that upon startup, timers 1-4 are already running by default.
   I was wondering which ones of them are used for functions like delay(), millis() etc.,
   and which ones are there for me to tweak.

   thanks

   Posted 5 years ago #
2. 

   crenn
   Moderator

   I believe that the systick timer is used for delay() and millis(). What do you mean by tweak?

   Posted 5 years ago #
3. 

   General Tree
   Member

   By tweak I mean to change the period of the counting, or the prescaler, or even turn it off, without it hurting the functions mentioned above.

   Posted 5 years ago #
4. 

   crenn
   Moderator

   All of them are available to tweak.

   Posted 5 years ago #
5. 

   General Tree
   Member

   Great, thanks.

   Any reason for them to be turned on by default if they dont do anything?

   Posted 5 years ago #
6. 

   gbulmer
   Moderator

   Any reason for them to be turned on by default if they dont do anything?

   Maybe partly because that's how the Arduino is set up. All of its timers are up and running. I am in favour of this because setting up the hardware is often one of the biggest hurdels for a beginner to overcome.

   I imagine it also makes some of the other code, like pwmWrite, a bit simpler if it can assume the timer is already going.

   Finally, the timers are doing something, they are running!-)
   So it is pretty straightforward to go look at a running timer to get a value. IMHO, this is very beginner friendly, and makes 'foraging' around the peripherals easier to get started on.

   Posted 5 years ago #
7. 

   mbolivar
   LeafLabs

   millis() does use systick, as crenn said. however, delay() is currently implemented in terms of delayMicroseconds(), which is just an empirically determined busy-wait in assembly. see time.c for the details:

   https://github.com/leaflabs/libmaple/blob/0.0.9/wirish/time.c

   the timers are initialized by default in init(), starting on line 68:

   https://github.com/leaflabs/libmaple/blob/0.0.9/wirish/wirish.c

   since a timer's prescaler and reset values are shared across all channels, altering those will affect pwm on all pins associated with the timer. here is a table you may find useful:
   http://leaflabs.com/docs/timers.html#caveats

   Posted 5 years ago #

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