The MMIO access framework consists of an abstraction for a contiguous
MMIO area with a base address set dynamically. Within this class 'Mmio'
are declarations for 'Register' and 'Subreg'. These two can be
parameterized statically via template parameters to create arbitrary
MMIO structures.
Whereas 'Register' relies to a POD like subregion of 'Mmio', 'Subreg'
relies to a MMIO region within a specific 'Register' and therefore is
smaller or equal then the storage type of its superior 'Register'.
Furthermore with 'Reg_array' and 'Subreg_array', there exists the
possibility to handle arrays of uniform contiguous registers or subregs
by index. 'Subreg_array' therefore abstracts from the width boundary of
its superior 'Register' and handles a steady distance between its
members in addition. Both also check array size limits.
Related to issue #69.
Until now, the RPC framework did not support const RPC functions. Rather
than being a limitation inherent to the concept, const RPC functions
plainly did not exist. So supporting them was not deemed too important.
However, there are uses of RPC interfaces that would benefit from a way
to declare an RPC function as const. Candidates are functions like
'Framebuffer::Session::mode()' and 'Input::Session::is_pending()'.
This patch clears the way towards declaring such functions as const.
Even though the patch is simple enough, the thorough support for
const-qualified RPC functions would double the number of overloads for
the 'call_member' function template (in 'base/include/util/meta.h'). For
this reason, the patch does support const getter functions with no
arguments only. This appears to be the most common use of such
functions.
