From 5eaf06d25c23a33a4e921161e9f0786a88e2948f Mon Sep 17 00:00:00 2001
From: David Phillips <david@yeah.nah.nz>
Date: Sun, 13 Dec 2020 21:11:50 +1300
Subject: Set a 2 second watchdog timer

---
 Makefile    |  2 +-
 altimeter.c | 16 +++++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 879452f..400aeff 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ QEMU_AVR ?= qemu-system-avr
 MCU ?= atmega32u4
 SIM_MCU ?= atmega2560
 CFLAGS += -DF_CPU=16000000UL -mmcu=$(MCU) -O3
-SIM_CFLAGS += -DF_CPU=16000000UL -mmcu=$(SIM_MCU) -g3 -gdwarf-2
+SIM_CFLAGS += -DF_CPU=16000000UL -mmcu=$(SIM_MCU) -g3 -gdwarf-2 -DWDT_DISABLE
 
 $(shell mkdir -p build/{real,sim})
 
diff --git a/altimeter.c b/altimeter.c
index 3133d2a..429976c 100644
--- a/altimeter.c
+++ b/altimeter.c
@@ -5,11 +5,21 @@
 
 #include <avr/sleep.h>
 #include <avr/interrupt.h>
+#include <avr/wdt.h>
 
 #include "barometer.h"
 #include "display.h"
 #include "util.h"
 
+#ifdef WDT_DISABLE
+# warning "WDT disabled in this build"
+# define WDT_SETUP_MAYBE(x)
+# define WDT_PAT_MAYBE()
+#else
+# define WDT_SETUP_MAYBE(x) do{wdt_enable(x);}while(0)
+# define WDT_PAT_MAYBE()    do{wdt_reset();}while(0)
+#endif
+
 /* ISR for collecting and displaying pressure, altitude data etc */
 ISR(TIMER1_COMPA_vect)
 {
@@ -69,7 +79,8 @@ ISR(TIMER1_COMPA_vect)
 	blank_to_eol(line, sizeof(line));
 	display_set_cursor(0, 3);
 	display_write(line);
-	return;
+
+	WDT_PAT_MAYBE();
 }
 
 int main(void)
@@ -92,6 +103,9 @@ int main(void)
 	USBCON &= ~(1 << USBE);
 #endif
 
+	/* main body should take no longer than 1 second to run */
+	WDT_SETUP_MAYBE(WDTO_2S);
+
 	sei();
 	while(1) {
 		set_sleep_mode(SLEEP_MODE_IDLE);
-- 
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