> Hi all,
>
> I am thinking of using the STM32H747XI for a project I'm working on. This
> particular chip has a CortexM7 and a Cortex M4. The chips access the
same
> memory map and can access and even share the same peripherals.
>
> Part of the problem, however, is that NuttX resets many
> registers/peripherals on boot. This is fine for when the M7 boots,
but when
> the M4 boots, resetting the RCC registers will ruin all the
initialization
> work the M7 has already done. Temporarily, I added a config variable to
> disable the clock reset on boot, but that's not the only place I'll
need to
> disable logic.
>
> So I have 2 questions:
>
> 1. Does anyone have any suggestions or comments for how to disable
some
> of the standard bring-up logic such as rcc_reset() or other peripheral
> resets? I can add CONFIG options, but I'm afraid of how many
options willl
> wind up needing to be added and it feels a little hacky.
You will need your own custom __start() logic and probably also
up_initialize() and board initialization logic.
> 2. Organizationally, how to handle the 2 cores? Currently, I've
added an
> option to the STM32H747I-Disco board that allows you to specify
which core
> you are using. Really all that does is switch which flash bank you are
> targeting by switching the linker script. The M4 and M7 can share
> instructions as long as double FPU is disabled for the M4. Does a
switch at
> the board level make sense? Or should this switch be at the arch level
> since it's technically the processor that's got the 2 cores?
I thought that the M4 was a different ISA? From what you say, I must be
mistaken.
So I would have thought it was two separate NuttX builds, with a
directory structure similar to nuttx/arch/arm/src/s32k1xx. There you
can see that there is a s32k11x subdirectory (Cortex M0) and a s32k14x
subdirectory (cortex M4). These are separate chips s32k1xx but the
directory organization would support dual builds for an heterogeneous
architecture.
If you intend to share code with a single build, I am not sure off the
top of my head the best way to do that. Certainly the start-up code
can't be shared. There are lots of other differences the M0 too:
interrupt controller, no BASEPRI register, etc. So that Cortex-M cannot
be shared either.
OpenAMP is also available (see nuttx/openamp).
> Thanks!
>
> -Anthony
