From f42df8c25b166ac0bd3bee232dd04a53050f1ff9 Mon Sep 17 00:00:00 2001
From: Charles Guan <3221512+charlesincharge@users.noreply.github.com>
Date: Thu, 2 Oct 2025 07:00:52 -0700
Subject: [PATCH] feat(wwdt): Add reset cause detection functionality

- Add ResetCause enum with all MSPM0 reset causes from TRM Table 2-9
- Add read_reset_cause() function to read SYSCTL.RSTCAUSE register
- Include helper methods to check for watchdog-specific resets
- Update wwdt example to demonstrate reset cause detection
- Register is automatically cleared after reading per MSPM0 spec

Fixes watchdog reset detection for debugging applications.
---
 embassy-mspm0/src/wwdt.rs           | 86 +++++++++++++++++++++++++++++
 examples/mspm0l1306/src/bin/wwdt.rs | 29 +++++++++-
 2 files changed, 114 insertions(+), 1 deletion(-)

diff --git a/embassy-mspm0/src/wwdt.rs b/embassy-mspm0/src/wwdt.rs
index e5c62c6602..86020b4fe3 100644
--- a/embassy-mspm0/src/wwdt.rs
+++ b/embassy-mspm0/src/wwdt.rs
@@ -240,6 +240,82 @@ impl ClosedWindowPercentage {
     }
 }
 
+/// Reset cause values from SYSCTL.RSTCAUSE register.
+/// Based on MSPM0 Technical Reference Manual Table 2-9.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+#[repr(u8)]
+pub enum ResetCause {
+    /// No reset since last read
+    NoReset = 0x00,
+    /// VDD < POR- violation, PMU trim parity fault, or SHUTDNSTOREx parity fault
+    PorHwFailure = 0x01,
+    /// NRST pin reset (>1s)
+    PorExternalNrst = 0x02,
+    /// Software-triggered POR
+    PorSwTriggered = 0x03,
+    /// VDD < BOR- violation
+    BorSupplyFailure = 0x04,
+    /// Wake from SHUTDOWN
+    BorWakeFromShutdown = 0x05,
+    /// Non-PMU trim parity fault
+    BootrstNonPmuParityFault = 0x08,
+    /// Fatal clock fault
+    BootrstClockFault = 0x09,
+    /// NRST pin reset (<1s)
+    BootrstExternalNrst = 0x0C,
+    /// Software-triggered BOOTRST
+    BootrstSwTriggered = 0x0D,
+    /// WWDT0 violation - This is the main watchdog reset cause we're interested in
+    SysrstWwdt0Violation = 0x0E,
+    /// BSL exit (if present)
+    SysrstBslExit = 0x10,
+    /// BSL entry (if present)
+    SysrstBslEntry = 0x11,
+    /// Uncorrectable flash ECC error (if present)
+    SysrstFlashEccError = 0x14,
+    /// CPU lockup violation
+    SysrstCpuLockupViolation = 0x15,
+    /// Debug-triggered SYSRST
+    SysrstDebugTriggered = 0x1A,
+    /// Software-triggered SYSRST
+    SysrstSwTriggered = 0x1B,
+    /// Debug-triggered CPURST
+    CpurstDebugTriggered = 0x1C,
+    /// Software-triggered CPURST
+    CpurstSwTriggered = 0x1D,
+}
+
+impl TryFrom<u8> for ResetCause {
+    type Error = u8;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        use ResetCause::*;
+        match value {
+            0x00 => Ok(NoReset),
+            0x01 => Ok(PorHwFailure),
+            0x02 => Ok(PorExternalNrst),
+            0x03 => Ok(PorSwTriggered),
+            0x04 => Ok(BorSupplyFailure),
+            0x05 => Ok(BorWakeFromShutdown),
+            0x08 => Ok(BootrstNonPmuParityFault),
+            0x09 => Ok(BootrstClockFault),
+            0x0C => Ok(BootrstExternalNrst),
+            0x0D => Ok(BootrstSwTriggered),
+            0x0E => Ok(SysrstWwdt0Violation),
+            0x10 => Ok(SysrstBslExit),
+            0x11 => Ok(SysrstBslEntry),
+            0x14 => Ok(SysrstFlashEccError),
+            0x15 => Ok(SysrstCpuLockupViolation),
+            0x1A => Ok(SysrstDebugTriggered),
+            0x1B => Ok(SysrstSwTriggered),
+            0x1C => Ok(CpurstDebugTriggered),
+            0x1D => Ok(CpurstSwTriggered),
+            other => Err(other),
+        }
+    }
+}
+
 #[non_exhaustive]
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 /// Watchdog Config
@@ -324,6 +400,16 @@ impl Watchdog {
     }
 }
 
+/// Read the reset cause from the SYSCTL.RSTCAUSE register.
+/// 
+/// This function reads the reset cause register which indicates why the last
+/// system reset occurred. The register is automatically cleared after being read,
+/// so this should be called only once per application startup.
+pub fn read_reset_cause() -> Result<ResetCause, u8> {
+    let cause_raw = pac::SYSCTL.rstcause().read().id();
+    ResetCause::try_from(cause_raw as u8)
+}
+
 pub(crate) trait SealedInstance {
     fn regs() -> &'static Regs;
 }
diff --git a/examples/mspm0l1306/src/bin/wwdt.rs b/examples/mspm0l1306/src/bin/wwdt.rs
index b8fb1a1cd4..f2f94806ce 100644
--- a/examples/mspm0l1306/src/bin/wwdt.rs
+++ b/examples/mspm0l1306/src/bin/wwdt.rs
@@ -8,7 +8,9 @@
 use defmt::*;
 use embassy_executor::Spawner;
 use embassy_mspm0::gpio::{Level, Output};
-use embassy_mspm0::wwdt::{ClosedWindowPercentage, Config, Timeout, Watchdog};
+use embassy_mspm0::wwdt::{
+    read_reset_cause, ClosedWindowPercentage, Config, ResetCause, Timeout, Watchdog,
+};
 use embassy_time::Timer;
 use {defmt_rtt as _, panic_halt as _};
 
@@ -20,6 +22,8 @@ async fn main(_spawner: Spawner) -> ! {
     let mut conf = Config::default();
     conf.timeout = Timeout::Sec1;
 
+    log_reset_cause();
+
     // watchdog also resets the system if the pet comes too early,
     // less than 250 msec == 25% from 1 sec
     conf.closed_window = ClosedWindowPercentage::TwentyFive;
@@ -52,3 +56,26 @@ async fn main(_spawner: Spawner) -> ! {
     //     Timer::after_millis(200).await;
     // }
 }
+
+fn log_reset_cause() {
+    // Check reset cause early in startup (register is cleared after reading)
+    match read_reset_cause() {
+        Ok(ResetCause::SysrstWwdt0Violation) => {
+            error!(
+                "🐕 System was reset due to WWDT0 timeout! Previous run failed to pet watchdog."
+            );
+        }
+        Ok(ResetCause::NoReset) => {
+            info!("✅ No reset since last read (first boot or register already read)");
+        }
+        Ok(ResetCause::PorExternalNrst) => {
+            info!("🔄 System reset via NRST pin");
+        }
+        Ok(other) => {
+            info!("🔄 System reset cause: {:?}", other);
+        }
+        Err(_) => {
+            warn!("❓ Unknown reset cause detected (reserved value)");
+        }
+    }
+}