watchdog configuration

src/hal/avr/cpu.cpp

@@ -10,7 +10,7 @@ void Init() {
 
 void Reset() {
     cli();
-    watchdog::Enable(0); //minimum amount of watchdog
+    watchdog::Enable(watchdog::configuration::compute(0)); //quickest watchdog reset
     for (;;)
         ; //endless loop while waiting for the watchdog to reset
 }

src/hal/avr/watchdog.cpp

@@ -4,8 +4,8 @@
 namespace hal {
 namespace watchdog {
 
-void Enable(uint16_t period) {
-    // @@TODO
+void Enable(const configuration &config) {
+    wdt_enable(config.prescalerBits);
 }
 
 void Disable() {

src/hal/watchdog.h

@@ -6,8 +6,40 @@ namespace hal {
 /// Hardware Abstraction Layer for the CPU's internal watchdog
 namespace watchdog {
 
+#if defined(__AVR__)
+constexpr uint32_t F_WDT = 128000; //frequency of the watchdog unit in Hz
+constexpr uint32_t basePrescaler = 2048; //what prescalerBits==0 actually does.
+constexpr uint8_t maxPrescaler = 9; //the maximum value prescalerBits can take
+constexpr uint8_t reloadBits = 0; //number of bits in the reload register
+#elif defined(__STM32__) //@todo to be changed to the final form
+constexpr uint32_t F_WDT = 32000; //frequency of the watchdog unit in Hz
+constexpr uint32_t basePrescaler = 4; //what prescalerBits==0 actually does.
+constexpr uint8_t maxPrescaler = 7; //the maximum value prescalerBits can take
+constexpr uint8_t reloadBits = 12; //number of bits in the reload register
+#endif
+
+struct configuration {
+    uint8_t prescalerBits;
+    uint16_t reload;
+
+public:
+    static constexpr configuration compute(float timeout) {
+        constexpr float tickPeriod = 1 / (float)F_WDT;
+        uint8_t prescalerBits = 0;
+        uint16_t reload = 0;
+        while (tickPeriod * (basePrescaler << prescalerBits) < timeout) {
+            prescalerBits++;
+        }
+        if (timeout)
+            reload = static_cast<uint16_t>(((timeout * (1 << reloadBits)) / (tickPeriod * (basePrescaler << prescalerBits)))) - 1;
+
+        configuration config = { prescalerBits, reload };
+        return config;
+    }
+};
+
 /// watchdog interface
-void Enable(uint16_t period);
+void Enable(const configuration &config);
 void Disable();
 void Reset();
 

src/main.cpp

@@ -97,7 +97,7 @@ void setup() {
 
     mt::timebase.Init();
 
-    watchdog::Enable(8000); //8s timeout
+    watchdog::Enable(watchdog::configuration::compute(8)); //set 8s timeout
 
     mg::globals.Init();