add Chapter 15 - runtime observer implementation

Chapter15/observer/hal/inc/hal.hpp

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <cstdint>
+
+#include <stm32f0xx_hal.h>
+
+namespace hal
+{
+inline void init()
+{
+    HAL_Init();
+}
+
+inline std::uint32_t get_pc() 
+{
+    std::uint32_t pc;
+    __asm volatile ("mov %0, pc" : "=r" (pc) );
+    return pc;
+}
+
+struct time
+{
+    static std::uint32_t get_ms()
+    {
+        return HAL_GetTick();
+    }
+
+    static void delay_ms(uint32_t delay) 
+    {
+        HAL_Delay(delay);
+    }
+};
+}; // namespace hal