#ifndef CONTROL_LOOP_INL_H
#define CONTROL_LOOP_INL_H

#include "board.h"
#include "bitband.h"

namespace hardware {

inline
bool ControlLoop::hw_button_enabled() const
{
  return MEM_ADDR(BITBAND(reinterpret_cast<uint32_t>(&(GPIOF->IDR)),
                          GPIOF_HW_SWITCH_PIN));
}


}

#endif


#ifndef CONTROL_LOOP_INL_H
#define CONTROL_LOOP_INL_H

#include "board.h"
#include "bitband.h"

namespace hardware {

inline
bool ControlLoop::hw_button_enabled()
{
  return MEM_ADDR(BITBAND(reinterpret_cast<uint32_t>(&(GPIOF->IDR)),
                          GPIOF_HW_SWITCH_PIN));
}


}

#endif


--- 
+++ 
@@ -7,7 +7,7 @@
 namespace hardware {
 
 inline
-bool ControlLoop::hw_button_enabled()
+bool ControlLoop::hw_button_enabled() const
 {
   return MEM_ADDR(BITBAND(reinterpret_cast<uint32_t>(&(GPIOF->IDR)),
                           GPIOF_HW_SWITCH_PIN));
Add const to hw_button_enabled() definition.
