stm32/rtc: cleanup and consolidate

examples/stm32f4/Cargo.toml

@@ -26,6 +26,7 @@ nb = "1.0.0"
 embedded-storage = "0.3.0"
 micromath = "2.0.0"
 static_cell = "1.0"
+chrono = { version = "^0.4", default-features = false}
 
 [profile.release]
 debug = 2

examples/stm32f4/src/bin/rtc.rs

@@ -0,0 +1,30 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use chrono::{NaiveDate, NaiveDateTime};
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_stm32::rtc::{Rtc, RtcConfig};
+use embassy_time::{Duration, Timer};
+use {defmt_rtt as _, panic_probe as _};
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_stm32::init(Default::default());
+    info!("Hello World!");
+
+    let now = NaiveDate::from_ymd_opt(2020, 5, 15)
+        .unwrap()
+        .and_hms_opt(10, 30, 15)
+        .unwrap();
+
+    let mut rtc = Rtc::new(p.RTC, RtcConfig::default());
+
+    rtc.set_datetime(now.into()).expect("datetime not set");
+
+    // In reality the delay would be much longer
+    Timer::after(Duration::from_millis(20000)).await;
+
+    let _then: NaiveDateTime = rtc.now().unwrap().into();
+}