rcc: Add reset reason calculation determination (#9)

The reset_reason submodule is used to determine the reset reason after a
reset.

As with the rest of the RCC code, this is adapted from same module in
stm32h7xx-hal.

src/rcc.rs

@@ -1 +1 @@
-
+mod reset_reason;

src/rcc/reset_reason.rs

@@ -0,0 +1,139 @@
+//! A module that can capture the RCC registers and read the reason why the mcu
+//! has reset
+
+use core::fmt::Display;
+
+/// Gets and clears the reason of why the mcu was reset
+#[rustfmt::skip]
+#[allow(dead_code)]
+pub fn get_reset_reason(rcc: &mut crate::stm32::RCC) -> ResetReason {
+    let reset_reason = rcc.rsr().read();
+
+    // Clear the register
+    rcc.rsr().modify(|_, w| w.rmvf().reset());
+
+    #[cfg(feature = "rm0492")]
+    // See R0492 Section 10.3.4 Reset source identification
+    return match (
+        reset_reason.lpwrrstf().is_reset_occurred(),
+        reset_reason.wwdgrstf().is_reset_occurred(),
+        reset_reason.iwdgrstf().is_reset_occurred(),
+        reset_reason.sftrstf().is_reset_occurred(),
+        reset_reason.borrstf().is_reset_occurred(),
+        reset_reason.pinrstf().is_reset_occurred(),
+    ) {
+        (false, false, false, false, true, true) => {
+            ResetReason::PowerOnReset
+        }
+        (false, false, false, false, false, true) => {
+            ResetReason::PinReset
+        }
+        (false, false, false, true, false, true) => {
+            ResetReason::SystemReset
+        }
+        (false, true, false, false, false, true) => {
+            ResetReason::WindowWatchdogReset
+        }
+        (false, false, true, false, false, true) => {
+            ResetReason::IndependentWatchdogReset
+        }
+        (true, false, false, false, false, true) => {
+            ResetReason::IllegalStopEntryReset
+        }
+        (false, true, true, false, false, true) => {
+            ResetReason::GenericWatchdogReset
+        }
+        _ => ResetReason::Unknown {
+            rcc_rsr: reset_reason.bits(),
+        },
+    };
+
+    #[cfg(feature = "rm0481")]
+    return ResetReason::Unknown { rcc_rsr: reset_reason.bits() }
+
+}
+
+/// Gives the reason why the mcu was reset
+#[derive(Debug, Copy, Clone)]
+#[allow(dead_code)]
+pub enum ResetReason {
+    /// The mcu went from not having power to having power and resetting
+    PowerOnReset,
+    /// The reset pin was asserted
+    PinReset,
+    /// The software did a soft reset through the AIRCR register of the M33 core
+    SystemReset,
+    /// The window watchdog triggered
+    WindowWatchdogReset,
+    /// The independent watchdog triggered
+    IndependentWatchdogReset,
+    /// Either or both of the two watchdogs triggered (but we don't know which one)
+    GenericWatchdogReset,
+    /// Illegal stop entry reset triggered
+    IllegalStopEntryReset,
+    /// The reason could not be determined
+    Unknown {
+        /// The raw register value
+        rcc_rsr: u32,
+    },
+}
+
+impl Display for ResetReason {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            ResetReason::PowerOnReset => write!(f, "Power-on reset"),
+            ResetReason::PinReset => write!(f, "Pin reset (NRST)"),
+            ResetReason::SystemReset => {
+                write!(f, "System reset generated by CPU (SYSRESETREQ)")
+            }
+            ResetReason::WindowWatchdogReset => write!(f, "WWDG reset"),
+            ResetReason::IndependentWatchdogReset => write!(f, "IWDG reset"),
+            ResetReason::GenericWatchdogReset => {
+                write!(f, "IWDG or WWDG reset")
+            }
+            ResetReason::IllegalStopEntryReset => {
+                write!(f, "Illegal stop entry reset")
+            }
+            ResetReason::Unknown { rcc_rsr } => write!(
+                f,
+                "Could not determine the cause. RCC RSR bits were 0x{:X}",
+                rcc_rsr
+            ),
+        }
+    }
+}
+
+#[cfg(feature = "defmt")]
+impl defmt::Format for ResetReason {
+    fn format(&self, f: defmt::Formatter<'_>) {
+        match self {
+            ResetReason::PowerOnReset => {
+                defmt::intern!("Power-on reset").format(f)
+            }
+            ResetReason::PinReset => {
+                defmt::intern!("Pin reset (NRST)").format(f)
+            }
+            ResetReason::SystemReset => {
+                defmt::intern!("System reset generated by CPU (SYSRESETREQ)")
+                    .format(f)
+            }
+            ResetReason::WindowWatchdogReset => {
+                defmt::intern!("WWDG reset").format(f)
+            }
+            ResetReason::IndependentWatchdogReset => {
+                defmt::intern!("IWDG reset").format(f)
+            }
+            ResetReason::GenericWatchdogReset => {
+                defmt::intern!("IWDG or WWDG reset").format(f)
+            }
+            ResetReason::IllegalStopEntryReset => {
+                defmt::intern!("Illegal stop entry reset").format(f)
+            }
+            ResetReason::Unknown { rcc_rsr } => defmt::write!(
+                f,
+                "Could not determine the cause. RCC RSR bits were 0x{:X}",
+                rcc_rsr
+            ),
+        }
+    }
+}