Add backup domain voltage regulator control

Author: mattico

src/pwr.rs

@@ -81,6 +81,7 @@ impl PwrExt for PWR {
                 any(feature = "rm0433", feature = "rm0399")
             ))]
             enable_vos0: false,
+            backup_regulator: false,
         }
     }
 }
@@ -97,6 +98,7 @@ pub struct Pwr {
         any(feature = "rm0433", feature = "rm0399")
     ))]
     enable_vos0: bool,
+    backup_regulator: bool,
 }
 
 /// Voltage Scale
@@ -332,6 +334,15 @@ impl Pwr {
         self
     }
 
+    /// Enable the backup domain voltage regulator
+    ///
+    /// The backup domain voltage regulator maintains the contents of backup SRAM
+    /// in Standby and VBAT modes.
+    pub fn backup_regulator(mut self) -> Self {
+        self.backup_regulator = true;
+        self
+    }
+
     pub fn freeze(self) -> PowerConfiguration {
         // NB. The lower bytes of CR3 can only be written once after
         // POR, and must be written with a valid combination. Refer to
@@ -418,7 +429,14 @@ impl Pwr {
 
         // Disable backup power domain write protection
         self.rb.cr1.modify(|_, w| w.dbp().set_bit());
-        let backup = unsafe { BackupREC::new_singleton() };
+        while self.rb.cr1.read().dbp().bit_is_clear() {}
+
+        if self.backup_regulator {
+            self.rb.cr2.modify(|_, w| w.bren().set_bit());
+            while self.rb.cr2.read().brrdy().bit_is_clear() {}
+        }
+
+        let backup = unsafe { BackupREC::new_singleton(self.backup_regulator) };
 
         PowerConfiguration {
             vos,

src/rcc/backup.rs

@@ -27,6 +27,7 @@
 pub struct BackupREC {
     #[cfg(feature = "rtc")]
     pub RTC: Rtc,
+    backup_regulator: bool,
 }
 
 impl BackupREC {
@@ -36,14 +37,20 @@ impl BackupREC {
     ///
     /// Must only be called once, after the backup domain write
     /// protection is disabled.
-    pub(crate) unsafe fn new_singleton() -> Self {
+    pub(crate) unsafe fn new_singleton(backup_regulator: bool) -> Self {
         Self {
             #[cfg(feature = "rtc")]
             RTC: Rtc {
                 _marker: core::marker::PhantomData,
             },
+            backup_regulator,
         }
     }
+
+    /// Returns `true` if the Backup Domain Voltage Regulator is enabled
+    pub fn backup_regulator_enabled(&self) -> bool {
+        self.backup_regulator
+    }
 }
 
 #[cfg(feature = "rtc")]