• Locked Locked
  • Replies 4 replies
  • Subscribers 119 subscribers
  • Views 7302 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Why nested interrupt corrupt Link Register?

Harri Wijaya
Note: This was originally posted on 13th June 2012 at http://forums.arm.com

hi,
Sorry for this basic question.

I find hard to understand why the Link Register can be corrupted in this below scenario:
1. IRQ interrupt occur.
2. IRQ ISR call a function foo(). (assume inside ISR, the IRQ interrupt is reenabled)
3. foo() is interrupted by another IRQ interrupt.

From what I understand:

*During (1):

STACK content:
some general purpose registers
LR_irq_1 (let call like that to indicate that the content is point to address of interrupted function by scenario-1)

LR_irq = address-1 (see LR_irq_1)

*During (2):

STACK content:
some general purpose registers
LR_irq_2
some general purpose registers
LR_irq_1

LR_irq = address-2 (address of a line within ISR)

*During (3):

STACK content:
some general purpose registers
LR_irq_3
some general purpose registers
LR_irq_2
some general purpose registers
LR_irq_1

LR_irq = address-3 (address of a line within foo() where second IRQ interrupt occur)


Assuming that we have enough IRQ stack size, then from above context, seem no reason for LR to be corrupted.

Any body could help me explain what causing LR to be corrupted?

Thanks!
Parents
  • Arm Employee Badge
    Note: This was originally posted on 15th June 2012 at http://forums.arm.com

    Making sure that you only enable the IRQ interrupt when in a different mode than IRQ will definitely fix the "LR_irq might be corrupted at any time" problem.  I won't promise it will fix ALL of your problems.  In particular, I've never liked the idea of my interrupts sharing their stack with USR mode* (which is what happens if you simply switch to SYS mode before re-enabling IRQs).  I'm sure there are ways of avoiding this problem but I haven't investigated it enough to give advice.  Good luck.

    • I think USR mode might do pretty much anything to SP_usr and IRQs still need to work.

        ...
        MOV r0, sp
        MOV sp, #-1
        ... ; IRQ happens here
        MOV sp, r0
        ...
Reply
  • Arm Employee Badge
    Note: This was originally posted on 15th June 2012 at http://forums.arm.com

    Making sure that you only enable the IRQ interrupt when in a different mode than IRQ will definitely fix the "LR_irq might be corrupted at any time" problem.  I won't promise it will fix ALL of your problems.  In particular, I've never liked the idea of my interrupts sharing their stack with USR mode* (which is what happens if you simply switch to SYS mode before re-enabling IRQs).  I'm sure there are ways of avoiding this problem but I haven't investigated it enough to give advice.  Good luck.

    • I think USR mode might do pretty much anything to SP_usr and IRQs still need to work.

        ...
        MOV r0, sp
        MOV sp, #-1
        ... ; IRQ happens here
        MOV sp, r0
        ...
Children
No data