[Tinyos-devel] Nested interrupts

[John Regehr]

To elaborate a bit on Phil's msg:

On AVR interrupt priorities come into play only when there are multiple 
pending interupts and the processor needs to choose one to fire.  This is 
counterintuitive for most of us who expect a model similar to Windows NT 
or most UNIX kernels where a higher-priority interrupt can nest on a 
lower-priority interrupt, but not the other way around.

AVR permits both nested and reentrant interrupts, where nesting means A 
preempts B and reentrancy means B preempts B.  The maximum depth of both 
reentrancy and nesting is limited only by stack constraints -- this has to 
be the case since the processor keeps no history regarding what interrupts 
are being processed.

Small puzzle problem: Is there ever a legitimate (i.e., correct and 
appropriate) use of a reentrant interrupt handler?

John Regehr



On Fri, 10 Aug 2007, Philip Levis wrote:

> On Aug 10, 2007, at 9:52 AM, Rodrigo Fonseca wrote:
> 
> > Hi,
> > 
> > in a project we are doing we need to take care of nested interrupts:
> > interrupts that fire while the processor is inside an interrupt
> > handler.
> > 
> > The question is, for each processor, is there a bound for the number
> > of nested interrupts we can have? Is that the number of different
> > interrupt priorities, or is it only bounded by the size of the stack
> > :) ?
> 
> 
> Size of the stack. E.g., an interrupt can be self-preemptive.
> 
> Phil
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