From a6f0ee374a44ffeb765669d43648fddbfee5a84e Mon Sep 17 00:00:00 2001
From: Mateusz Nowak <118080320+mateusznowakdev@users.noreply.github.com>
Date: Fri, 23 May 2025 01:05:00 +0200
Subject: [PATCH] machine/samd21: implement watchdog

---
 src/machine/machine_atsamd21.go | 59 +++++++++++++++++++++++++++++++++
 src/machine/machine_atsamd51.go |  3 +-
 src/machine/watchdog.go         |  2 +-
 3 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/src/machine/machine_atsamd21.go b/src/machine/machine_atsamd21.go
index e0c5f2cc29..f193d7ba6e 100644
--- a/src/machine/machine_atsamd21.go
+++ b/src/machine/machine_atsamd21.go
@@ -2027,3 +2027,62 @@ func checkFlashError() error {
 
 	return nil
 }
+
+// Watchdog provides access to the hardware watchdog available
+// in the SAMD21.
+var Watchdog = &watchdogImpl{}
+
+const (
+	// WatchdogMaxTimeout in milliseconds (16s)
+	WatchdogMaxTimeout = (16384 * 1000) / 1024
+)
+
+type watchdogImpl struct{}
+
+// Configure the watchdog.
+//
+// This method should not be called after the watchdog is started and on
+// some platforms attempting to reconfigure after starting the watchdog
+// is explicitly forbidden / will not work.
+func (wd *watchdogImpl) Configure(config WatchdogConfig) error {
+	// Use OSCULP32K as source for Generic Clock Generator 8, divided by 32 to get 1.024kHz
+	sam.GCLK.GENDIV.Set(sam.GCLK_CLKCTRL_GEN_GCLK8 | (32 << sam.GCLK_GENDIV_DIV_Pos))
+	sam.GCLK.GENCTRL.Set(sam.GCLK_CLKCTRL_GEN_GCLK8 | (sam.GCLK_GENCTRL_SRC_OSCULP32K << sam.GCLK_GENCTRL_SRC_Pos) | sam.GCLK_GENCTRL_GENEN)
+	waitForSync()
+
+	// Use GCLK8 for watchdog
+	sam.GCLK.CLKCTRL.Set(sam.GCLK_CLKCTRL_ID_WDT | (sam.GCLK_CLKCTRL_GEN_GCLK8 << sam.GCLK_CLKCTRL_GEN_Pos) | sam.GCLK_CLKCTRL_CLKEN)
+
+	// Power on the watchdog peripheral
+	sam.PM.APBAMASK.SetBits(sam.PM_APBAMASK_WDT_)
+
+	// 1.024kHz clock
+	cycles := int((int64(config.TimeoutMillis) * 1024) / 1000)
+
+	// period is expressed as a power-of-two, starting at 8 / 1024ths of a second
+	period := uint8(0)
+	cfgCycles := 8
+	for cfgCycles < cycles {
+		period++
+		cfgCycles <<= 1
+
+		if period >= 0xB {
+			break
+		}
+	}
+
+	sam.WDT.CONFIG.Set(period << sam.WDT_CONFIG_PER_Pos)
+
+	return nil
+}
+
+// Starts the watchdog.
+func (wd *watchdogImpl) Start() error {
+	sam.WDT.CTRL.SetBits(sam.WDT_CTRL_ENABLE)
+	return nil
+}
+
+// Update the watchdog, indicating that `source` is healthy.
+func (wd *watchdogImpl) Update() {
+	sam.WDT.CLEAR.Set(sam.WDT_CLEAR_CLEAR_KEY)
+}
diff --git a/src/machine/machine_atsamd51.go b/src/machine/machine_atsamd51.go
index d169eab995..15d0f142fb 100644
--- a/src/machine/machine_atsamd51.go
+++ b/src/machine/machine_atsamd51.go
@@ -2357,6 +2357,5 @@ func (wd *watchdogImpl) Start() error {
 
 // Update the watchdog, indicating that `source` is healthy.
 func (wd *watchdogImpl) Update() {
-	// 0xA5 = magic value (see datasheet)
-	sam.WDT.CLEAR.Set(0xA5)
+	sam.WDT.CLEAR.Set(sam.WDT_CLEAR_CLEAR_KEY)
 }
diff --git a/src/machine/watchdog.go b/src/machine/watchdog.go
index d818a00860..7dbf676ad2 100644
--- a/src/machine/watchdog.go
+++ b/src/machine/watchdog.go
@@ -1,4 +1,4 @@
-//go:build nrf52840 || nrf52833 || rp2040 || rp2350 || atsamd51 || atsame5x || stm32
+//go:build nrf52840 || nrf52833 || rp2040 || rp2350 || atsamd21 || atsamd51 || atsame5x || stm32
 
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