Description

The STM32 microcontrollers are currently among the most popular, out of the many models I dare say the STM32F103C8 is probably one of the most well known of the microcontrollers from ST, mainly because of its inclusion in the Blue Pill board, which is extremely popular in the maker space.

Bare metal development on ST microcontroller is made easier because of the Hardware Abstraction Layer (HAL) that the manufacturer provides, which, as the name implies, allows abstracting hardware operations to API functions that are supposed to be the same independent of the specific device. This abstraction allows easier and faster development, the flip side of this is that register operations are obscured, although they’re still accessible and can be operated on.

My long introduction on these subjects is to understand the reason why I’m writing this; while the STM32F103 is extremely popular, it’s not usually used in low power operations, and posts and examples on how to work with this specific device are not abundant. My attempt here is to provide some hints on how to work with STOP mode in the device and use the RTC Alarms for periodic wake ups.

The creation of a STM32Cube project is outside the scope of the project, however I do want to point out that for this to work out the configuration on the RTC the RTC OUT option should be set to “RTC Output on the Tamper pin”, this option enables the Alarm configuration. Using STM32Cube MX is the easiest way to set up the project, although is possible to change the configuration later on editing the code. The following figure shows how the configuration should be made on STM32Cube MX for the RTC.