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ARM1136 - Not Jumping to ISR problem

NikhilWipro NikhilWipro
Note: This was originally posted on 6th January 2009 at http://forums.arm.com

Hi,

I am working on ARM1136JF-S Core. I need to implement handling of the interrupts (GPT interrupt) in u-boot bootloader which is not generally done.

For this I followed the following steps
1) mask I/F Bit in cpsr register to enable the IRQ.
2) Set VE bit ( bit 24 ) to 0 in the CP15 register - for fixed vector
3) Set V bit (bit 13) to 0 to set the address range 0x00000000-0x0000001C


I have called my ISR "IRQ_Handler" also in the appropriate place. The below snippet demonstrates how I am doing the same.

.globl _start
_start: b reset

ldr pc, _undefined_instruction
ldr pc, _software_interrupt
ldr pc, _prefetch_abort
ldr pc, _data_abort
ldr pc, _not_used
ldr pc, _irq
ldr pc, _fiq

_undefined_instruction: .word undefined_instruction
_software_interrupt: .word software_interrupt
_prefetch_abort: .word prefetch_abort
_data_abort:  .word data_abort
_not_used:  .word not_used
_irq:   .word irq
_fiq:   .word fiq

irq:
get_irq_stack
irq_save_user_regs
bl IRQ_Handler
irq_restore_user_regs

With the above snippet and register setting and after enabling the interrupt, I am able to get the interrupt but my board goes to hang state. May be the control is not jumping to the appropriate location after getting the interrupts.

Please let me know if I am missing on something. Would really appreciate some pointers on this.

Thanks in Advance.

-Nikhil
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  • +1 Arm Employee Badge
    Note: This was originally posted on 6th January 2009 at http://forums.arm.com

    1) mask I/F Bit in cpsr register to enable the IRQ.

    Just to confirm: You need to clear the I bit. The F bit is irrelevant if you are using IRQs as it controls FIQs, but you would do best to leave it as it is.

    With the above snippet and register setting and after enabling the interrupt, I am able to get the interrupt but my board goes to hang state. May be the control is not jumping to the appropriate location after getting the interrupts.

    Do you know where it does jump to? Can you connect a debugger?

    irq:
    get_irq_stack
    irq_save_user_regs
    bl IRQ_Handler
    irq_restore_user_regs

    What does "get_irq_stack" do? It is conventional to set up the IRQ stack before enabling IRQs.

    Also, check that you're writing to the correct CP15 register. Indeed, I often get confused with the syntax of the coprocessor instructions. You should be modifying the Control Register, c1.

    Finally, check that your modification of the interrupt behaviour does not conflict with the system. For example, if your system already uses FIQs (or any other exception) for some reason, you will need to take care not to disrupt this behaviour.

    Does that help?
    Jacob
Reply
  • +1 Arm Employee Badge
    Note: This was originally posted on 6th January 2009 at http://forums.arm.com

    1) mask I/F Bit in cpsr register to enable the IRQ.

    Just to confirm: You need to clear the I bit. The F bit is irrelevant if you are using IRQs as it controls FIQs, but you would do best to leave it as it is.

    With the above snippet and register setting and after enabling the interrupt, I am able to get the interrupt but my board goes to hang state. May be the control is not jumping to the appropriate location after getting the interrupts.

    Do you know where it does jump to? Can you connect a debugger?

    irq:
    get_irq_stack
    irq_save_user_regs
    bl IRQ_Handler
    irq_restore_user_regs

    What does "get_irq_stack" do? It is conventional to set up the IRQ stack before enabling IRQs.

    Also, check that you're writing to the correct CP15 register. Indeed, I often get confused with the syntax of the coprocessor instructions. You should be modifying the Control Register, c1.

    Finally, check that your modification of the interrupt behaviour does not conflict with the system. For example, if your system already uses FIQs (or any other exception) for some reason, you will need to take care not to disrupt this behaviour.

    Does that help?
    Jacob
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