This is the mail archive of the mailing list for the eCos project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Interrupt vs Thread - shared resource

I have read the documentation before, and the main problem is what you are mentioning too. You cannot call blocking instructions, such as |cyg_semaphore_wait, so if a thread used the shared resource when the scheduler started the DSR (we use semaphores) the DSR cannot wait. You would say we are not allowed to use blocking instructions in DSR context, but locking the DSR, masking the interrupt, or locking the scheduler has the same effect, the DSR code is blocked (not at the theoretical ||cyg_semaphore_wait, ||but at the "start") (or it is an event worth solution than allow ||cyg_semaphore_wait (rework the implementation of semphores)).

Thank you!
Gergely Szentirmai

Paul D. DeRocco Ãrta:
From: Reg

Thank your for your answer!

I understand, and agree with all the stuff that you wrote (the need of ISR, DSR, and the solution). The only reason why I'm calling these solutions "hack" (in the meaning, that not the best soulution (workaround) ), because the code is depending on the calling "enviroment", so the code is somehow application specific.
If for ex. semaphores could be used in DSRs, the code would be better, because the implementation of the semaphore would handle this group of questions (if you are in a thread, if you are in a DSR etc)
So in other words, when you write a procedure, you have to think about "what will call this procedure/ or use the shared resource". If only threads use a resource, you use mutex. If a thread and a DSR is using it, you have to lock scheduler or mask the interrupt or lock the specific DSR, just because no sinchronization object can be used in DSRs.

I think allowing the use of sinchronization objects in DSRs would be a great feature from eCos (would need to modify the implemetation of semaphore, mutex etc.)
+ better code quality
+ faster developement
+ less bugs...
- a bit more time/resource

So if DSRs are an interface or an intermediate layer between the "interrupt world" and the "thread world", why are we not allowed to use sinc. objects?

Ah, I see your fundamental problem. You've misread the documentation if you think all these functions aren't usable in DSR context. Most are, as long as you don't use a function that may block. Read the bit at the end of each function description in the Reference Manual for details about the valid contexts they can be used in.

-- Before posting, please read the FAQ: and search the list archive:

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]