A very basic version can now be found in the addrqual branch:
Declaring a named address space:
__adressmod <set> <name>;
where set should be a function taking no arguments and name is the name
of the new address space. sdcc will then ensure that set is executed
before each access to a variable in the address space name (and no set
function of another address space is executed).
E.g.
void set1(void);
void set2(void);
__adressmod set1 space1;
__adressmod set2 space2;
space1 int i, j;
space2 int k;
void f(void)
{
k = i + j;
}
in f set1() will be called first, then i and j will be added, then
set2() will be called and the result of the addition will be stored in k.
The idea is that the set functions does some magic (set some page
register, i/o location or memory mapped whatever) necessary to map the
variables in the named address space into the physical address space.
This allows for a flexible approach to bankswitching.
Next steps:
* Tell the linker about it, i.e. put i and j into a section named space1
instead of the generic _DATA.
* Fix bugs (so far this is only very lightly tested and only on
Z80/Z180/R2K) Other ports and more complicated operations, like pointer
lookup with pointers residing in one named address space pointing to a
variable in another address space or passing variables as arguments
might currently be broken.
* More efficient placement of the calls to set function (this is NP-hard
in general, but I have some ideas about using the limited tree-width of
the control-flow graph to approach this problem).
* Implement __adressmod read1 write1 space1; which would give named
address spaces for memory that cannot be mapped into the processor's
physical address space.
Philipp
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