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ISeed
ISeed
Associate III
April 26, 2019
Question

Setting RTC Alarm For A Specific Period From Now

  • April 26, 2019
  • 4 replies
  • 1628 views

Hello,

I would like to set an RTC alarm to wake the system, let's say, 5 seconds from current time.

The example applications show how to set an alarm for a specific date+time in the future, but I want to set it for X milliseconds from current time.

One way would be to get the current timestamp in milliseconds and add X to it, convert it to date+time and set RTC alarm to it.

Another way would be if there is some RTC date+time algebra support, where I can just take a date+time and add milliseconds to it.

I have no idea how to do either.

Can you please advice me on how to solve this?

Thanks!

This topic has been closed for replies.

4 replies

Vangelis Fortounas
Vangelis Fortounas
Associate II
April 30, 2019

for STM32F10x is very simple to do this by setting the alarm reg to sum of the desired value in seconds and RTC counter.

For the other families, converting time_date to seconds , add desired value and convert it back to date_time can be done by using C lib time functions (#include <time.h>.

Consider use "RTC periodic wakeup unit" with settable values from a tenth of millisecond to 36 hours. You can find a lot of details here.

ISeed
ISeedAuthor
Associate III
April 30, 2019

Well, seems like I'm in luck. STM32F100RBT was chosen, which, from my understanding, fall under STM32F10x .

Could you recommend example project that demonstrate this?

JAN R
JAN R
Associate III
April 30, 2019

I use RTC ALARM A on my STM32L152. When I need wakeup in 5 second from current time I just read the actual time then I add 5 second to it and then new time I set to ALARM reg. It works reliably.

ISeed
ISeedAuthor
Associate III
April 30, 2019

How do you add 5 seconds? Is there a function to add X seconds to a time struct, or you have your own module that changes the entire struct according to added delta? (that is, if current time is 1999:12:31:23:59:59, and you want to add 5 seconds, you make it into 2000:01:01:00:00:04)?

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