[ell-i-developers] Re: Instructions before asynchronous exception

  • From: Ivan Raul <supra.material@xxxxxxxxx>
  • To: ell-i-developers@xxxxxxxxxxxxx
  • Date: Wed, 5 Feb 2014 14:50:06 +0200

Hi to All.

Regarding the user mode and supervisor mode, on Cortex M-0 it implements
the ARMv6-M
 base architecture, where all software runs on privileged mode.

However, Cortex M-4 is a different story, as it implements ARMv7-M, which
has both modes available on Thread mode (Handler mode is always privileged)

As a design decision, what is the general idea when using the Cortex M-4
processor, will be a distinction between the user application and the
system below it, or all the software will be developed as if it runs in
privileged mode (as now on the Cortex M-0 processor of the Ellduino)?

With Warm Regards, Ivan Raul

On Wed, Feb 5, 2014 at 7:38 AM, Pekka Nikander <pekka.nikander@xxxxxx>wrote:

> > I am trying to find out how many instructions can be executed between an
> asynchronous exception is triggered and the handler is entered (for making
> sure that the behaviour of PendSV is the desired one, as at some point we
> will use blocking synchronization primitives)
> My suggestion would be to use a synchronous interrupt for entering from a
> blocking primitive, e.g. SVCall.  Remember too that if we don't have a
> separate user mode and supervisor mode, it may be sufficient just to block
> the interrupts and do the thing there, on the spot, not to separately enter
> an interrupt routine through a vector.  That would save a number of cycles
> as well, making the primitive faster.
> > For Cortex M-0, i can't find it... Does anyone know about any reference
> or document where it can be found, just to speed up the searching process?
> At least I don't know, but hopefully someone else does?
> --Pekka

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