[ECOS] Interrupt vs Thread - shared resource

Szentirmai Gergely gergely.szentirmai@axelero.hu
Thu Feb 12 18:10:00 GMT 2009

Guys, thank you for your answers!
Scheduler lock is an alternative to mask the interrupt, but masking the 
specific interrupt (or lock the specific DSR) is maybe better in 
performance, but too application specific (code reuse).
As I read the scheduler manual:
"However there is one situation where locking the scheduler is 
appropriate: if some data structure needs to be shared between an 
application thread and a DSR associated with some interrupt source, the 
thread can use the scheduler lock to prevent concurrent invocations of 
the DSR and then safely manipulate the structure."
It writes the same thing.
So there are two possible solution only; lock the scheduler, or mask the 
Programatically I think both solution are not "pretty" enough, because I 
have to write procedures, that bother with these "hacks" (they are not 
high level enough), rather than use a mutex, but this is an eCos 
conceptional problem (what a shame, not too user-friendly), I think...
Thank you for this dsr_lock idea too!
Gergely Szentirmai

Robert Brusa írta:
> On Thu, 12 Feb 2009 02:58:03 +0100, Szentirmai Gergely 
> <gergely.szentirmai@axelero.hu> wrote:
>> Hello
>> I describe my problem with a simplified example: I have a thread, 
>> which works with a buffer, and an ISR (or DSR), which would add some 
>> byte to this buffer too, so it is a shared resource. Since it is 
>> unable wait for a flag, or mutex in ISR, when the thread's code 
>> working with the buffer, the interrupt can jam the data.
>> The only solution is to disable the interrupt for that critical 
>> section in the thread? Isn't there a better solution?
>> I hope I was clear.
>> Thanks!
>> Gergely Szentirmai
> Well, you might block just this particular interrupt while messing around
> in the DSR using cyg_drv_interrupt_mask(vector) and enable it after the
> critical section using the correspoding unmask-routine. This would 
> still allow other interrupts to come through.
> When a "normal" task accesses critical data that are also accessed by 
> a DSR use cyg_drv_dsr_lock() etc.....
> Happy with this? Regards
>    Robert

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