Re: [ECOS] IRQ interrupt at highest priority

[Jesper Skov <jskov at redhat dot com>]

>>>>> "Amlan" == Amlan Chakraborty <amlan.cha@wipro.com> writes:

Amlan> I want my IRQ interrupt handler (attached to a specific
Amlan> hardware interrupt) at the highest priority.

Amlan> Infact when ecos is using some of the harware interrupts (like
Amlan> TIMER2 for RTC) for scheduling and other work it should catch
Amlan> my interrupt and not miss it.

Amlan> I found in file clock.cxx ,the interrupt for RTC is created
Amlan> with priority 1.Is any other interrupt created by the OS with
Amlan> higher priority (i.e. 0)? If I create an interrupt with
Amlan> priority 0 will it serve the purpose?

If you attach an ISR to some other vector than TIMER2, a TIMER2
interrupt will not cause it to be executed, regardless of its
priority.

If you try to attach it to TIMER2, it will probably fail since that
vector is already in use for the real-time clock ISR. In other words,
if you attach an ISR to a vector, it is the only ISR on that vector
and you need not be concerned that some other ISR gets the interrupt
before your ISR.

The exception is when you configure with interrupt chaining. In this
case it's possible to register more than one ISR with on the same
vector. In this case the ISRs must be careful only to return HANDLED
if they actually an interrupt. See Cyg_Interrupt::chain_isr for
the sematic details. 

There is yet an exception, come to think of it: if a vector is used
for more than one interrupt source, you may want to write an arbiter
which will either perform further interrupt decoding to determine the
actual interrupt source and call the appropriate ISR, or simply call
all possible related ISRs in the same fashion as the chaining_isr. See
hal/powerpc/mpc8xx/.../src/var_intr.c for an example of an interrupt
arbiter.

Jesper