Periodic RTC wakeup without LSE

[stgedas]

Posted on January 24, 2013 at 13:39

Hi,

I'm trying to make STM32F3 device wake up from sleep using LSI. According to datasheet it should not require LSE for such operation. I do get no wakeup interrupt if I don't connect 32khz external crystall or disable LSE by software. Maybe it could be a problem with my code, but I see the same behaviour on IAR examples too (''StdPeriph_Lib\Project\StdPeriph_Examples\RTC\RTC_LSI'')

I've tried that on STM32L-discovery too. Results are the same. Does anyone tried to run STM32 RTC wakeup functions without external crystal?

Gedas

[Tesla DeLorean]

Posted on January 24, 2013 at 18:04

The problem with most STM32's is that ONLY the LSE is in the backup power domain, powered via VBAT. ALL the other supplies turn off, and clocks STOP as a result.

Place the LSE parts.

[stgedas]

Posted on January 24, 2013 at 19:54

Thanks for the reply. In my case I wasn't going to remove power from all other power pins during low power mode. So my testes were with full powered device. The missing interrupt was even if the device was in active mode. Anyway, as you say, I'll add LSE.

[Tesla DeLorean]

Posted on January 24, 2013 at 20:06

Certain modes gate off the internal regulators (1.2 V), or clocks.

You should be able use WFI type sleeping, and see a SysTick, or other interrupts with longer periodicity.

Standby obviously gets more complicated as you have exit via a reset and catch that in the status registers.

Haven't spent too much time with the F3's but did a lot of low power and sleeping via RTC on F1's.

[damh]

Posted on June 28, 2013 at 10:33

If the RTC is only used to periodicly wakeup the MCU (short periods up to about 30s) and the value of the RTC is unimportant, you can abuse the IWDG for that purpose ;) It runs in Standbymode and LSI keeps running in this case and the MCU can be wakeuped from the IWDG from all low power modes.

[Tesla DeLorean]

Posted on June 28, 2013 at 12:45

What's the power consumption look like for that?