Re: Protected Objects and Interrupt Handlers

[Tero Koskinen <tero.koskinen@iki.fi>]

Hi,

25.2.2016, 18.02, Simon Wright wrote:
> Maciej Sobczak <see.my.homepage@gmail.com> writes:
>
>> Last but no least - Simon has pointed you towards an article (a
>> book chapter, in fact) where the interrupts are handled by regular
>> procedures instead - as an author of that text I feel responsible
>> for clarifying why - the reason is that the book consistently
>> assumes a zero-runtime execution platform, where the necessary
>> scaffolding for protected objects (namely: actual synchronization)
>> simply does not exist.
>
> A minor point: a common cited advantage of the Cortex series is that
> ISRs can be written in ordinary code, without compiler magic. This
> seems to imply that other MCUs _do_ need compiler magic!

Yes, ARM Cortex-Mx family processors can have normal C functions as
interrupt handlers because when the interrupt occurs the hardware pushes
a set of registers to stack automatically (and also restores
the registers when returning from the interrupt).

On the other hand, 8-bit AVRs do not have this feature, so for them you
need to mark the interrupt handler somehow so that the compiler can
generate different code for them.

In general, ARM Cortex-Mx processors are "C-friendly". For example
in the normal case, you can have all the startup code in C (or
in Ada, which is then exported to C) and there is no need for
assembler.

Yours,
  Tero