Difference between revisions of "How RL78 manages named address spaces"
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Pointers into '''__far''' address spaces cannot be passed as arguments to library functions. Likewise, library functions such as '''malloc''' that allocate memory do so only for the generic address space ('''__near'''); there are no standard functions for allocating space in the '''__far''' address spaces. | Pointers into '''__far''' address spaces cannot be passed as arguments to library functions. Likewise, library functions such as '''malloc''' that allocate memory do so only for the generic address space ('''__near'''); there are no standard functions for allocating space in the '''__far''' address spaces. | ||
| − | More detailed information about named | + | More detailed information about named address spaces can be found [http://std.dkuug.dk/jtc1/sc22/wg14/www/docs/n1005.pdf here] |
Latest revision as of 14:32, 30 April 2017
RL78 contains 2 address spaces:
Near address space
- qualifier __near
- 16 bit addresses
- saved in the topmost 64 kB of the address space
Far address space
- qualifier __far
- 20 bit addresses
The default (generic) address space for the RL78 targets is the __near address space. For now there is no option available to make the __far address space the default one.
Below are a few examples of the way __far address space can be used:
Examples:
__far char a, b, c; // Declares three characters in address space __far
struct { int a; char b; } * __far q;
// Declares a pointer in address space __far that points to a structure in the generic space (__near)
There are some constraints on the use of address-space type qualifiers:
Since address space __far encloses address space __near, then every location (address) within __near is also within __far.
The most significant constraint is that an address space name cannot be used to qualify an object that has automatic storage duration. This implies, in particular, that variables declared inside a function cannot be allocated in a named address space unless they are also explicitly declared as static or extern.
void X()
{
__far char a;
}
//compilation errror
For the examples above, the declarations of a, b, c, and q would have to be outside any function to be valid.
As determined by its type, every pointer points into a specific address space, either the generic address space or a named address space. A pointer into an address space can only point to locations in that address space (including any subset address spaces).
Pointers into __far address spaces cannot be passed as arguments to library functions. Likewise, library functions such as malloc that allocate memory do so only for the generic address space (__near); there are no standard functions for allocating space in the __far address spaces.
More detailed information about named address spaces can be found here
