Verify the main app mostly sleeps

This validates that the main watch app spends at
least 99.5% of it's time sleeping in the first 10
seconds.

firmware/Bsp/Drivers/LowPower.cpp

@@ -31,9 +31,19 @@ namespace BSP {
 
 using BSP::ReturnCode;
 
+GpioPin *LowPower::m_timing_pin = nullptr;
+
 ReturnCode LowPower::init()
 {
-    enable_debug();
+    m_timing_pin = nullptr;
+    return ReturnCode::OK;
+}
+
+ReturnCode LowPower::init(GpioPin &timing_pin)
+{
+    m_timing_pin = &timing_pin;
+    m_timing_pin->write(0);
+
     return ReturnCode::OK;
 }
 
@@ -93,7 +103,13 @@ ReturnCode LowPower::stop()
     CLR(RCC->CFGR, RCC_CFGR_STOPWUCK); // MSI oscillator is wake-up from stop clock
     SET(SCB->SCR, SCB_SCR_SLEEPDEEP_Msk); // low-power mode = stop mode
 
-    __WFI(); // enter low-power mode (Wake from interrupt)
+    if (m_timing_pin != nullptr) {
+        m_timing_pin->write(1);
+        __WFI(); // enter low-power mode (Wake from interrupt)
+        m_timing_pin->write(0);
+    } else{
+        __WFI();
+    }
 
     wakeups++;