Jump to reset vector when program exceeds specified watchdog timeout

src/bus/i2c.c

@@ -12,8 +12,9 @@
 #define TW_MR_SLA_NACK  0x48
 #define TW_MR_DATA_ACK  0x50
 
-// XXX: Handle interrupts in I2C_vect ISR? This may not
-// actually be much better than the blocking approach
+// XXX: Error handling and recovery without watchdog timer.
+// XXX: Implement I2C_vect ISR? This may not actually be
+// much better than the blocking approach.
 
 static void I2C_AHT20_Reset(void);
 static bool I2C_AHT20_IsCalibrated(void);

src/bus/mosfet.c

@@ -1,6 +1,9 @@
 #include "common.h"
 #include "bus/mosfet.h"
 
+// XXX: This might be too much specificity for something where
+// a generic digital output implementation would be adequate.
+
 int MOS_Init(void)
 {
 	// PB0: MOSFET #1 Peltier

src/common/watchdog.c

@@ -43,16 +43,16 @@ void WDT_Enable(void)
 	WDTCR = BIT(WDE) | BIT(WDP2) | BIT(WDP1) | BIT(WDP0);
 }
 
-void WDT_SetTimeout(unsigned char time)
+void WDT_SetTimeoutFlag(unsigned char flag)
 {
-	time = CLAMP(time, 7, 0);
+	flag = CLAMP(flag, 7, 0);
 
-	Info("Setting watchdog prescalar to %d...", time);
+	Info("Setting watchdog prescalar to %02X...", flag);
 
 	// Clear timer prescalar flags
 	WDTCR &= 0xF8; // 11111000
 
-	WDTCR |= time;
+	WDTCR |= flag;
 }
 
 bool WDT_HasTriggered(void)
@@ -88,8 +88,8 @@ bool WDT_HasTriggered(void)
 void WDT_Disable(void)
 {
 	// WDE can only be cleared if the WDTOE bit has
-	// logic level one. To disable an enabled Watchdog
-	// Timer, the following procedure must be followed:
+	// logic level one. To disable an enabled watchdog
+	// timer, the following procedure must be followed:
 
 	// 1. In the same operation, write a logic one to
 	// WDTOE and WDE. A logic one must be written to WDE
@@ -97,7 +97,7 @@ void WDT_Disable(void)
 	// operation starts.
 
 	// 2. Within the next four clock cycles, write a
-	// logic 0 to WDE. This disables the Watchdog
+	// logic 0 to WDE. This disables the watchdog.
 
 	// No interrupts while we set WDTCR;
 	ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
@@ -108,5 +108,13 @@ void WDT_Disable(void)
 
 void WDT_Reset(void)
 {
-	// TODO: Reset watchdog timer
+	// The WDR – Watchdog Reset – instruction resets the
+	// watchdog timer. The Watchdog Timer is also reset
+	// when it is disabled and when a chip reset occurs.
+
+	// If the reset period expires without another
+	// watchdog reset, the chip resets and executes from
+	// the Reset Vector.
+
+	__asm__("WDR");
 }

src/common/watchdog.h

@@ -4,7 +4,7 @@
 #include <stdbool.h>
 
 void WDT_Enable(void);
-void WDT_SetTimeout(unsigned char time);
+void WDT_SetTimeoutFlag(unsigned char flag);
 bool WDT_HasTriggered(void);
 void WDT_Disable(void);
 void WDT_Reset(void);

src/main.c

@@ -7,13 +7,14 @@
 #include <avr/interrupt.h>
 
 // TODO: Convert raw data from ADS1115 to usable values.
-// TODO: Implement optional sensor value check with CRC8.
-// TODO: Set timeouts for polling based things like I2C.
-// TODO: Write an improved serial parser (low priority).
+// TODO: Implement optional CRC8 sensor measurement check.
 // TODO: Either implement software PWM for the FAN03 timer
 // (which will be quite complicated) or pick a chip with
 // more than two 16-bit PWM outputs like the ATmega328PB.
 // https://www.mikrocontroller.net/articles/Soft-PWM
+// TODO: Check if FAN02 is receiving the right frequency.
+// TODO: Write an improved command parser (low priority).
+// TODO: Proper error handling and recovery (after testing).
 
 int Init(void)
 {
@@ -48,8 +49,8 @@ int Init(void)
 	if (WDT_HasTriggered())
 		Info("Unexpected system reset.");
 
-	// WDT_Enable();
-	// WDT_SetTimeout(7);
+	WDT_Enable();
+	WDT_SetTimeoutFlag(0x7); // 2 seconds
 
 	// There is a possiblity to use interrupt signals
 	// for I2C communication but only as one large
@@ -98,8 +99,6 @@ void Update(void)
 	float temp[3], rhum[3];
 	short raw[4];
 
-	WDT_Reset(); // Reset watchdog
-
 	Info("Reading sensor values...");
 
 	I2C_SetChannel(AHT01);
@@ -128,7 +127,9 @@ int main(void)
 	Init();
 
 	for (;;) {
+		WDT_Reset();
 		Update();
+		WDT_Reset();
 		Sleep(1000);
 	}