Re: [avr-gcc-list] External 256K FLASH - memory pointer

[Richard Weickelt]

Hi,

> I do not know if there will be any code over head due to C++.
> Unfortunately my forte is 'C'. Can I trouble you for some
> examples/sample code please? Thank you once again.

Use a 32-bit unsigned integer and a typedef as it has been suggested and 
You're done. It would be foolish to move on to C++ in an existing project.

For fun You can try to translate Your code with avr-g++. It should compile 
and library functions seem to work even without declaring them as extern 
"C", but may have side effects. Most of the language core is backward 
compatible to C.

Many stereotypes exist about the inefficiency of C++ and some of them 
contain a grain of truth. Try it Yourself and have a deep look into 
Stroustrup's "The C++ programming language", which is worth every cent.

The following code example may look dumb, because it does nothing really 
interesting. But the point is: By defining all those operators manually You 
gain full control over type conversion and You can not mix up internal and 
external addresses. Many operators are missing, so take it as a hint for 
further experiments.

// Everything related to address calculation and conversion
class ExtFlashAddr
{
public:
        // ExtFlashAddr myAddr = ExtFlashAddr(0x4711)
        inline explicit ExtFlashAddr(uint32_t address = 0);
        // Copy constructor
        inline ExtFlashAddr(const ExtFlashAddr& other);
        // ExtFlashAddr myAddr = otherAddr
        inline ExtFlashAddr& operator=(const ExtFlashAddr& other);
        // myAddr++
        inline ExtFlashAddr& operator++();

        friend ExtFlashAddr operator+(const ExtFlashAddr&, const ExtFlashAddr&);

private:
        uint32_t addr;
};

inline ExtFlashAddr operator+(const ExtFlashAddr& addr1, const ExtFlashAddr& 
addr2);

// Access functions
class ExtFlashTools
{
public:
        static void read(void* dst, const ExtFlashAddr& src, size_t size);
        static void erase(const ExtFlashAddr& src, size_t size);
        static void write(const ExtFlashAddr& dst, void const* src, size_t 
size);

};


ExtFlashAddr::ExtFlashAddr(uint32_t address)
{
        this->addr = address;
}

ExtFlashAddr::ExtFlashAddr(const ExtFlashAddr& other)
{
        this->addr = other.addr;
}


ExtFlashAddr& ExtFlashAddr::operator=(const ExtFlashAddr& other)
{
        this->addr = other.addr;
        return *this;
}

ExtFlashAddr& ExtFlashAddr::operator++()
{
        addr++;
        return *this;
}

ExtFlashAddr operator+(const ExtFlashAddr& addr1, const ExtFlashAddr& addr2)
{
        return ExtFlashAddr(addr1.addr + addr2.addr);
}


The code above should be optimized away with -Os.