Timer with prescaling

RE: Timer with prescaling

Karl Ylvisaker — Tue, 24 Mar 2020 15:01:00 GMT

Hello Jiemde,

[quote user="Jiemde"]I'm not yet "comfortable" with sdk.config[/quote]

I completely understand, no problem at all.

Have you seen the TIMER API Reference? Particularly, bit_width is set during initialization - see the input parameters to the nrfx_timer_init function.
I think this is what you are looking for, rather than the sdk_config.h. The lines you are referring to in the sdk_config is the DEFAULT_CONFIG parameters.

Is this what you were looking for?
Please let me know if you should have more questions or encounter any other issues! :)

Best regards,
Karl

RE: Timer with prescaling

Jean-marie — Tue, 24 Mar 2020 13:55:08 GMT

Hi Karl, Thanks for fast reply.

I'm not yet "comfortable" with sdk.config, so for the "BITMODES", I suppose you speak about:

// <o> TIMER_DEFAULT_CONFIG_MODE - Timer mode or operation

// <0=> Timer
// <1=> Counter

#ifndef TIMER_DEFAULT_CONFIG_MODE
#define TIMER_DEFAULT_CONFIG_MODE 0
#endif

// <o> TIMER_DEFAULT_CONFIG_BIT_WIDTH - Timer counter bit width

// <0=> 16 bit
// <1=> 8 bit
// <2=> 24 bit
// <3=> 32 bit

#ifndef TIMER_DEFAULT_CONFIG_BIT_WIDTH
#define TIMER_DEFAULT_CONFIG_BIT_WIDTH 3
#endif

Question: where can I set the timer prescaler ?

Is there an example for references ?

Best regards

Jiemde

RE: Timer with prescaling

Karl Ylvisaker — Tue, 24 Mar 2020 10:18:31 GMT

Hi,

Have you seen the Timer documentation regarding prescaler options?

As you see from the prescaler register, you may at most set the timer prescaler to 2^9, which gives you 16M / 512 = 31250 ticks per second.
So, then we need to establish the size of our TIMER. We see that the different BITMODES available ranges from 8 to 32 bit.
Setting it to 32 bit gives us 4294967296 ticks til overflow, which with the 512 prescaler gives us ~36 hours till overflow.
Thus, you may set the timer to compare for the value 2700000000 - which is ticks per second times seconds in 24h.

You will now receive a COMPARE event every 24h. When this happens, you should remember to also CLEAR your timer - to avoid counting all the way to 36h before restarting at 0.

Is this what you were looking for?

Best regards,
Karl