Is it possible to create an Exact 1ms wakeup period using RTC in Stm32l1 series controller? if yes, How it can be done?Â

[Aswin Farzana Mohamed Ansar]

Posted on March 24, 2017 at 12:35

(ref:

AN4759)

Configuration 1 - able to achieve ~1ms but not exactly 1 ms.

Configuration 2 - not able to achieve 1 ms but successfully achieved 1s as the least period and can program in multiples of it.

[waclawek.jan]

Posted on March 25, 2017 at 01:10

You need to use a crystal which is an integer multiple of 1kHz, i.e. not the 32.768kHz crystal. 40kHz might be one of the options. The dividers then have to be adjusted accordingly.

JW

[Aswin Farzana Mohamed Ansar]

Posted on March 29, 2017 at 08:16

Thank you Jan.

I achieved 1 ms wakeup period by setting prediv_a as 36 and prediv_s as 0 using LSI 37kHz on the nucleo l152re.

LSI as RTC clock

Time base = ((36 + 1) * (0 + 1)) / 37Khz = 1ms

[Aswin Farzana Mohamed Ansar]

Posted on March 29, 2017 at 08:21

The mistake i made was trying to set the prescalers without properly entering the Init mode. Rectified that and thus achieved 1 ms wakeup timebase.

I now have a question, my ck_spre clock frequency is 1 Khz. This ck_spre is the calendar clock.

What would be the effect on the RTC Time value?