The existing code is functional but inccorrect and blindly modifies the
other masking bits. It is important to preserve those other bits since
they control masking of important system events.
Certain input parameters for MMU mapping operations could cause an
infinite recursion if block end boundaries didn't align to 4k. This
ensures that recursion descent does not exceed 2 levels and instead
rounds up to the nearest 4k block if necessary.
This moves the AArch64 MMU memory type definitions into cpukit for use
by libdebugger since remapping of memory is required to insert software
breakpoints.
Currently, the AArch64 BSPs have a hard time running on real hardware
without building the toolchain and the bsps with -mstrict-align in
multiple places. Configuring the MMU on these chips allows for unaligned
memory accesses for non-device memory which avoids requiring strict
alignment in the toolchain and in the BSPs themselves.
In writing this driver, it was found that the synchronous exception
handling code needed to be rewritten since it relied on clearing SCTLR_EL1 to
avoid thread stack misalignments in RTEMS_DEBUG mode. This is now
avoided by exactly preserving thread mode stack and flags and the new
implementation is compatible with the draft information provided on the
mailing list covering the Exception Management API.
