Added RTC domain backup registers support.

Author: akashihi

src/rtc.rs

@@ -466,6 +466,22 @@ impl Rtc {
 
         result
     }
+
+    /// Read content of the backup register.
+    ///
+    /// The registers retain their values during wakes from standby mode or system resets. They also
+    /// retain their value when Vdd is switched off as long as V_BAT is powered.
+    pub fn read_backup_register(&self, register: usize) -> u32 {
+        self.rtc.bkpr[register].read().bits()
+    }
+
+    /// Set content of the backup register.
+    ///
+    /// The registers retain their values during wakes from standby mode or system resets. They also
+    /// retain their value when Vdd is switched off as long as V_BAT is powered.
+    pub fn write_backup_register(&self, register: usize, value: u32) {
+        unsafe { self.rtc.bkpr[register].write(|w| w.bits(value)) }
+    }
 }
 
 /// The RTC wakeup timer