Manipulation of Memory Mapped Registers using C++ Templates (Technique from Olivier Gillet's Avril AVR Library)

memory_mapped_io.cpp

#include <stdio.h>
#include <stdint.h>


////  Create some pretend Memory Mapped Registers
volatile uint64_t memory_mapped_registers[] = {0, 0, 0, 0, 0, 0, 0, 0, 0};

#define bit_depth uint64_t
#define mmio_byte(mem_addr) (*(volatile bit_depth *)(mem_addr))

////  Create 8 fake registers
#define R0 mmio_byte(memory_mapped_registers + 0)
#define R1 mmio_byte(memory_mapped_registers + 1)
#define R2 mmio_byte(memory_mapped_registers + 2)
#define R3 mmio_byte(memory_mapped_registers + 3)
#define R4 mmio_byte(memory_mapped_registers + 4)
#define R5 mmio_byte(memory_mapped_registers + 5)
#define R6 mmio_byte(memory_mapped_registers + 6)
#define R7 mmio_byte(memory_mapped_registers + 7)


////  A struct wrapper around a register
#define IORegister(reg)                                 \
  struct reg##Register {                                \
    static volatile bit_depth *ptr(){                   \
      return &reg;                                      \
    }                                                   \
    reg##Register &operator=(const bit_depth &value){   \
      *ptr() = value;                                   \
      return *this;                                     \
    }                                                   \
  };


IORegister(R0);
IORegister(R1);
IORegister(R2);
IORegister(R3);
IORegister(R4);
IORegister(R5);
IORegister(R6);
IORegister(R7);


////
//  Control of one bit in a register
template <typename Register, uint8_t bit>
struct BitInRegister {
  static void clear(){
    *Register::ptr() &= ~(1 << bit);
  }
  static void set(){
    *Register::ptr() |= (1 << bit);
  }
  static void toggle(){
    *Register::ptr() ^= (1 << bit);
  }
  static bit_depth value(){
    return *Register::ptr() & (1 <<bit) ? 1 : 0;
  }
};


////
//  A resource that can make us get pizza for dinner, by specifying bits in the registers
template <typename PizzaEnableBit, typename DinnerTimeBit, typename FullOfFoodBit>
struct FoodController {
  typedef PizzaEnableBit Pizza;
  typedef DinnerTimeBit Dinner;
  typedef FullOfFoodBit Full;

  static inline void eat_pizza_for_dinner(){
    Pizza::set();
    Dinner::set();
  }

  static inline void pizza_done(){
    Pizza::clear();
    Dinner::clear();
    Full::set();
  }
};

////  Shorthand type that knows about these specific bits.
typedef FoodController< BitInRegister<R4Register, 5>, 
            BitInRegister<R1Register, 2>, BitInRegister<R7Register, 7> > PizzaController;


int main(void){

  PizzaController::eat_pizza_for_dinner();


  for(int i = 0; i < 8; i++){
    printf("R%d: %lld\n", i, memory_mapped_registers[i]);
  }

  PizzaController::pizza_done();

  for(int i = 0; i < 8; i++){
    printf("R%d: %lld\n", i, memory_mapped_registers[i]);
  }

  return 0;
}