The maximum length of time interrupts are disabled

[Angelo Fraietta]

Fabrizio Sebastiani wrote:

> Hi all,
>     I have a question a general arch-indipendent question (Im using 
> sparc-rtems 4.0.0 for ERC32)
> about the maximum length of time interrupts are disabled, regarding 
> invocation of rtems_interrupt_{disable,enable} routines.
>     My question is how can I be sure that one critical section never 
> miss an interrupt?
>     Suppose to have such a tipical code:
>
> rtems_isr_level il;
>
> rtems_interrupt_disable(il);
> // ... critical section ....
> rtems_interrupt_enable(il);
>
>     Its clear to me that critical section have to perform the minimum 
> actions in order to be "fast";
>     Suppose that an interrupt comes while the CPU is executing the 
> critical section.
> How i can be sure that my critical section does not take too much time 
> before the re-enabling of the interrupt? How i can be sure that no 
> critical sections will
> miss some interrupt that was coming inside them?
>     I found some infos in the RTEMS docs:
>     For example, as explained in 
> http://www.rtems.com/onlinedocs/releases/4.0.0/doc/c_user/a00078.html
>     says that I should have a look at the spart architecture supplement:
> http://www.rtems.org/onlinedocs/releases/rtemsdocs-4.6.0/share/rtems/html/supplements/sparc/sparc00032.html 
>
>     In this link there is only a statement that is obscure to me and 
> it doesnt seem to answer to my original question:

I had this vey problem in that I missessome interrupts because I 
disabled interrupts, when All I needed to do was modify what I was doing.
First see if you need to disable interrupts. If you just want to stop 
another task from being prempted, I think that you can change the 
priority of your task to be the highest (check on that)
If you need to disable interrupts, make sure the code that s within that 
section is as small as possible.

Here asre a couple of articles that I found helpful.
http://www.embedded.com/story/OEG20010918S0052
http://www.embedded.com/story/OEG20020426S0100
 

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Angelo Fraietta

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