For M-profile CPUs, the range from 0xe0000000 to 0xe00fffff is the
Private Peripheral Bus range, which includes all of the memory mapped
devices and registers that are part of the CPU itself, including the
NVIC, systick timer, and debug and trace components like the Data
Watchpoint and Trace unit (DWT). Within this large region, the range
0xe000e000 to 0xe000efff is the System Control Space (NVIC, system
registers, systick) and 0xe002e000 to 0exe002efff is its Non-secure
alias.
The architecture is clear that within the SCS unimplemented registers
should be RES0 for privileged accesses and generate BusFault for
unprivileged accesses, and we currently implement this.
It is less clear about how to handle accesses to unimplemented
regions of the wider PPB. Unprivileged accesses should definitely
cause BusFaults (R_DQQS), but the behaviour of privileged accesses is
not given as a general rule. However, the register definitions of
individual registers for components like the DWT all state that they
are RES0 if the relevant component is not implemented, so the
simplest way to provide that is to provide RAZ/WI for the whole range
for privileged accesses. (The v7M Arm ARM does say that reserved
registers should be UNK/SBZP.)
Expand the container MemoryRegion that the NVIC exposes so that
it covers the whole PPB space. This means:
* moving the address that the ARMV7M device maps it to down by
0xe000 bytes
* moving the off and the offsets within the container of all the
subregions forward by 0xe000 bytes
* adding a new default MemoryRegion that covers the whole container
at a lower priority than anything else and which provides the
RAZWI/BusFault behaviour
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201119215617.29887-2-peter.maydell@linaro.org
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