Array of pointers like (*(volatile unsigned long *)0x40004000)

Question

I am having a very hard time figuring out how to solve the following problem. I am on an embedded system with very little memory and want to minimize memory usage. Pointers

Answer 1

Usual way is to declare a struct, for example :

struct RegsAtAddrA
{
  unsigned int array1[10];
  char val1;
  // etc
};

then to access it :

volatile RegsAtAddrA *pRegsA = (volatile RegsAtAddrA *) 0x40004000;
pRegsA->val1= 'a';
//etc

EDIT: I just realized that I haven't answered the question. So, here it is :

#include <iostream>
unsigned long a=1;
unsigned long b=2;
volatile unsigned long *port_base_array[] = {
   &a,
   &b,
   //etc
};
int main()
{
    std::cout<<"a="<<*port_base_array[0]<<std::endl;
    std::cout<<"b="<<*port_base_array[1]<<std::endl;
}

Answer 2

I don't know why @Etienne deleted his answer, but it contained the essential information: The address is cast to volatile unsigned long *. That's what you need an array of.

typedef volatile unsigned long* reg_addr;

reg_addr registers[] = {
  &GPIO_PORTA_BASE,
  &GPIO_PORTB_BASE,
  // ...
};

We need to take the address again (&GPIO_PORTA_BASE), since the macro automatically dereferences them. Access as:

*registers[i] &= your_value;

Answer 3

What I think you're trying to do is something like this:

volatile unsigned long * gpio_porta = &GPIO_PORTA_BASE;

If you're using C++, you could also do the following:

volatile unsigned long & reg_foo = (&GPIO_PORTA_BASE)[3];
volatile unsigned long & reg_foo = gpio_porta[3];

And use it as:

reg_foo &= 0x1;

However, most times I would expect a base address register to actually be stored as a pointer, rather than as the dereference of the pointer. Because of that, I would probably want your macros to be defined as:

#define GPIO_PORTA_BASE      ((volatile unsigned long *) 0x40004000)
#define GPIO_PORTB_BASE      ((volatile unsigned long *) 0x40005000)

And then you could simply access them as

GPIO_PORTA_BASE[3] &= 0x1

Answer 4

If I'm getting you right, this should be enough:

volatile unsigned long* GPIO_PORTA = (volatile unsigned long*) 0x40004000;

You could use that as

volatile unsigned long regxx = GPIO_PORTA[0x17];

// even

GPIO_PORTA[10] &= 0xF000;